Re: net/core: BUG in copy_net_ns()

[ebiederm@xmission.com (Eric W. Biederman)]

zzoru <zzoru007@gmail.com> writes:

> net/core: BUG in copy_net_ns() (net_namespace.c)

I don't understand this failure report at all.

I don't see the connection to copy_net_ns().  And I don't see how the
suggested patch short of covering up a memory stomp could possibly make
a difference.

What am I missing?


> Hello,
>
> I've got the following error report while fuzzing the kernel with syzkaller.
>
> On commit 1bdbe227492075d058e37cb3d400e6468d0095b5
>
> Syzkaller hit 'WARNING in __alloc_pages_slowpath' bug.
>
> syz-executor561 (17453) used greatest stack depth: 25056 bytes left
> WARNING: CPU: 0 PID: 692 at mm/page_alloc.c:4415
> __alloc_pages_slowpath+0x1cb1/0x2220 mm/page_alloc.c:4386
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 0 PID: 692 Comm: kswapd0 Not tainted 5.0.0-rc1+ #4
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> Ubuntu-1.8.2-1ubuntu1 04/01/2014
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0xca/0x13e lib/dump_stack.c:113
>  panic+0x278/0x5bf kernel/panic.c:214
>  __warn.cold.10+0x20/0x45 kernel/panic.c:571
>  report_bug+0x246/0x2d0 lib/bug.c:186
>  fixup_bug arch/x86/kernel/traps.c:178 [inline]
>  do_error_trap+0x123/0x1e0 arch/x86/kernel/traps.c:271
>  do_invalid_op+0x31/0x40 arch/x86/kernel/traps.c:290
>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
> RIP: 0010:__alloc_pages_slowpath+0x1cb1/0x2220 mm/page_alloc.c:4415
> Code: 8b 84 24 a8 00 00 00 e9 ea f1 ff ff 85 d2 0f 85 0b 01 00 00 48 c7
> c7 c0 5e 55 84 e8 79 f8 23 02 e9 86 f9 ff ff 44 8b 74 24 0c <0f> 0b 48
> b8 00 00 00 00 00 fc ff df 48 8b 54 24 18 48 c1 ea 03 80
> RSP: 0018:ffff8880683fedb8 EFLAGS: 00010046
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1ffff1100d07fda4
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807ffdd528
> RBP: dffffc0000000000 R08: 0000000000000000 R09: 000000000000067a
> R10: 0000000000000000 R11: ffff88807ffdc487 R12: 0000000000000000
> R13: ffff8880683ff010 R14: 0000000000415a00 R15: ffff8880683ff010
>  __alloc_pages_nodemask+0x521/0x5f0 mm/page_alloc.c:4555
>  __alloc_pages include/linux/gfp.h:473 [inline]
>  __alloc_pages_node include/linux/gfp.h:486 [inline]
>  kmem_getpages mm/slab.c:1398 [inline]
>  cache_grow_begin+0x95/0x300 mm/slab.c:2666
>  fallback_alloc+0x1ce/0x270 mm/slab.c:3208
>  __do_cache_alloc mm/slab.c:3345 [inline]
>  slab_alloc mm/slab.c:3373 [inline]
>  kmem_cache_alloc+0x286/0x2f0 mm/slab.c:3541
>  create_object+0x83/0x880 mm/kmemleak.c:578
>  kmemleak_alloc_recursive include/linux/kmemleak.h:55 [inline]
>  slab_post_alloc_hook mm/slab.h:442 [inline]
>  slab_alloc mm/slab.c:3381 [inline]
>  kmem_cache_alloc+0x18f/0x2f0 mm/slab.c:3541
>  mempool_alloc+0x13e/0x340 mm/mempool.c:385
>  bio_alloc_bioset+0x36f/0x5d0 block/bio.c:489
>  bio_alloc include/linux/bio.h:393 [inline]
>  submit_bh_wbc.isra.57+0x128/0x680 fs/buffer.c:3061
>  __block_write_full_page+0x6e8/0xcd0 fs/buffer.c:1765
>  block_write_full_page+0x202/0x250 fs/buffer.c:2955
>  pageout mm/vmscan.c:865 [inline]
>  shrink_page_list+0x220f/0x3800 mm/vmscan.c:1383
>  shrink_inactive_list+0x3c2/0xaa0 mm/vmscan.c:1961
>  shrink_list mm/vmscan.c:2273 [inline]
>  shrink_node_memcg.constprop.83+0x4bf/0x10e0 mm/vmscan.c:2538
>  shrink_node+0x162/0xd10 mm/vmscan.c:2753
>  kswapd_shrink_node mm/vmscan.c:3516 [inline]
>  balance_pgdat+0x47f/0xc00 mm/vmscan.c:3674
>  kswapd+0x57c/0xde0 mm/vmscan.c:3929
>  kthread+0x347/0x410 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> Syzkaller reproducer:
> # {Threaded:false Collide:false Repeat:true RepeatTimes:0 Procs:8
> Sandbox:none Fault:false FaultCall:-1 FaultNth:0 EnableTun:false
> UseTmpDir:true EnableCgroups:false EnableNetdev:true ResetNet:false
> HandleSegv:false Repro:false Trace:false}
> unshare(0x40000000)
>
>
> C reproducer:
> // autogenerated by syzkaller (https://github.com/google/syzkaller)
>
> #define _GNU_SOURCE
>
> #include <arpa/inet.h>
> #include <dirent.h>
> #include <endian.h>
> #include <errno.h>
> #include <fcntl.h>
> #include <net/if.h>
> #include <net/if_arp.h>
> #include <netinet/in.h>
> #include <sched.h>
> #include <signal.h>
> #include <stdarg.h>
> #include <stdbool.h>
> #include <stdint.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/ioctl.h>
> #include <sys/mount.h>
> #include <sys/prctl.h>
> #include <sys/resource.h>
> #include <sys/socket.h>
> #include <sys/stat.h>
> #include <sys/syscall.h>
> #include <sys/time.h>
> #include <sys/types.h>
> #include <sys/uio.h>
> #include <sys/wait.h>
> #include <time.h>
> #include <unistd.h>
>
> #include <linux/if_addr.h>
> #include <linux/if_ether.h>
> #include <linux/if_link.h>
> #include <linux/if_tun.h>
> #include <linux/in6.h>
> #include <linux/ip.h>
> #include <linux/neighbour.h>
> #include <linux/net.h>
> #include <linux/netlink.h>
> #include <linux/rtnetlink.h>
> #include <linux/tcp.h>
> #include <linux/veth.h>
>
> unsigned long long procid;
>
> static void sleep_ms(uint64_t ms)
> {
>   usleep(ms * 1000);
> }
>
> static uint64_t current_time_ms(void)
> {
>   struct timespec ts;
>   if (clock_gettime(CLOCK_MONOTONIC, &ts))
>     exit(1);
>   return (uint64_t)ts.tv_sec * 1000 + (uint64_t)ts.tv_nsec / 1000000;
> }
>
> static void use_temporary_dir(void)
> {
>   char tmpdir_template[] = "./syzkaller.XXXXXX";
>   char* tmpdir = mkdtemp(tmpdir_template);
>   if (!tmpdir)
>     exit(1);
>   if (chmod(tmpdir, 0777))
>     exit(1);
>   if (chdir(tmpdir))
>     exit(1);
> }
>
> static bool write_file(const char* file, const char* what, ...)
> {
>   char buf[1024];
>   va_list args;
>   va_start(args, what);
>   vsnprintf(buf, sizeof(buf), what, args);
>   va_end(args);
>   buf[sizeof(buf) - 1] = 0;
>   int len = strlen(buf);
>   int fd = open(file, O_WRONLY | O_CLOEXEC);
>   if (fd == -1)
>     return false;
>   if (write(fd, buf, len) != len) {
>     int err = errno;
>     close(fd);
>     errno = err;
>     return false;
>   }
>   close(fd);
>   return true;
> }
>
> static struct {
>   char* pos;
>   int nesting;
>   struct nlattr* nested[8];
>   char buf[1024];
> } nlmsg;
>
> static void netlink_init(int typ, int flags, const void* data, int size)
> {
>   memset(&nlmsg, 0, sizeof(nlmsg));
>   struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg.buf;
>   hdr->nlmsg_type = typ;
>   hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
>   memcpy(hdr + 1, data, size);
>   nlmsg.pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
> }
>
> static void netlink_attr(int typ, const void* data, int size)
> {
>   struct nlattr* attr = (struct nlattr*)nlmsg.pos;
>   attr->nla_len = sizeof(*attr) + size;
>   attr->nla_type = typ;
>   memcpy(attr + 1, data, size);
>   nlmsg.pos += NLMSG_ALIGN(attr->nla_len);
> }
>
> static void netlink_nest(int typ)
> {
>   struct nlattr* attr = (struct nlattr*)nlmsg.pos;
>   attr->nla_type = typ;
>   nlmsg.pos += sizeof(*attr);
>   nlmsg.nested[nlmsg.nesting++] = attr;
> }
>
> static void netlink_done(void)
> {
>   struct nlattr* attr = nlmsg.nested[--nlmsg.nesting];
>   attr->nla_len = nlmsg.pos - (char*)attr;
> }
>
> static int netlink_send(int sock)
> {
>   if (nlmsg.pos > nlmsg.buf + sizeof(nlmsg.buf) || nlmsg.nesting)
>     exit(1);
>   struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg.buf;
>   hdr->nlmsg_len = nlmsg.pos - nlmsg.buf;
>   struct sockaddr_nl addr;
>   memset(&addr, 0, sizeof(addr));
>   addr.nl_family = AF_NETLINK;
>   unsigned n = sendto(sock, nlmsg.buf, hdr->nlmsg_len, 0,
>                       (struct sockaddr*)&addr, sizeof(addr));
>   if (n != hdr->nlmsg_len)
>     exit(1);
>   n = recv(sock, nlmsg.buf, sizeof(nlmsg.buf), 0);
>   if (n < sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))
>     exit(1);
>   if (hdr->nlmsg_type != NLMSG_ERROR)
>     exit(1);
>   return -((struct nlmsgerr*)(hdr + 1))->error;
> }
>
> static void netlink_add_device_impl(const char* type, const char* name)
> {
>   struct ifinfomsg hdr;
>   memset(&hdr, 0, sizeof(hdr));
>   netlink_init(RTM_NEWLINK, NLM_F_EXCL | NLM_F_CREATE, &hdr, sizeof(hdr));
>   if (name)
>     netlink_attr(IFLA_IFNAME, name, strlen(name));
>   netlink_nest(IFLA_LINKINFO);
>   netlink_attr(IFLA_INFO_KIND, type, strlen(type));
> }
>
> static void netlink_add_device(int sock, const char* type, const char* name)
> {
>   netlink_add_device_impl(type, name);
>   netlink_done();
>   int err = netlink_send(sock);
>   (void)err;
> }
>
> static void netlink_add_veth(int sock, const char* name, const char* peer)
> {
>   netlink_add_device_impl("veth", name);
>   netlink_nest(IFLA_INFO_DATA);
>   netlink_nest(VETH_INFO_PEER);
>   nlmsg.pos += sizeof(struct ifinfomsg);
>   netlink_attr(IFLA_IFNAME, peer, strlen(peer));
>   netlink_done();
>   netlink_done();
>   netlink_done();
>   int err = netlink_send(sock);
>   (void)err;
> }
>
> static void netlink_add_hsr(int sock, const char* name, const char* slave1,
>                             const char* slave2)
> {
>   netlink_add_device_impl("hsr", name);
>   netlink_nest(IFLA_INFO_DATA);
>   int ifindex1 = if_nametoindex(slave1);
>   netlink_attr(IFLA_HSR_SLAVE1, &ifindex1, sizeof(ifindex1));
>   int ifindex2 = if_nametoindex(slave2);
>   netlink_attr(IFLA_HSR_SLAVE2, &ifindex2, sizeof(ifindex2));
>   netlink_done();
>   netlink_done();
>   int err = netlink_send(sock);
>   (void)err;
> }
>
> static void netlink_device_change(int sock, const char* name, bool up,
>                                   const char* master, const void* mac,
>                                   int macsize)
> {
>   struct ifinfomsg hdr;
>   memset(&hdr, 0, sizeof(hdr));
>   if (up)
>     hdr.ifi_flags = hdr.ifi_change = IFF_UP;
>   netlink_init(RTM_NEWLINK, 0, &hdr, sizeof(hdr));
>   netlink_attr(IFLA_IFNAME, name, strlen(name));
>   if (master) {
>     int ifindex = if_nametoindex(master);
>     netlink_attr(IFLA_MASTER, &ifindex, sizeof(ifindex));
>   }
>   if (macsize)
>     netlink_attr(IFLA_ADDRESS, mac, macsize);
>   int err = netlink_send(sock);
>   (void)err;
> }
>
> static int netlink_add_addr(int sock, const char* dev, const void* addr,
>                             int addrsize)
> {
>   struct ifaddrmsg hdr;
>   memset(&hdr, 0, sizeof(hdr));
>   hdr.ifa_family = addrsize == 4 ? AF_INET : AF_INET6;
>   hdr.ifa_prefixlen = addrsize == 4 ? 24 : 120;
>   hdr.ifa_scope = RT_SCOPE_UNIVERSE;
>   hdr.ifa_index = if_nametoindex(dev);
>   netlink_init(RTM_NEWADDR, NLM_F_CREATE | NLM_F_REPLACE, &hdr,
> sizeof(hdr));
>   netlink_attr(IFA_LOCAL, addr, addrsize);
>   netlink_attr(IFA_ADDRESS, addr, addrsize);
>   return netlink_send(sock);
> }
>
> static void netlink_add_addr4(int sock, const char* dev, const char* addr)
> {
>   struct in_addr in_addr;
>   inet_pton(AF_INET, addr, &in_addr);
>   int err = netlink_add_addr(sock, dev, &in_addr, sizeof(in_addr));
>   (void)err;
> }
>
> static void netlink_add_addr6(int sock, const char* dev, const char* addr)
> {
>   struct in6_addr in6_addr;
>   inet_pton(AF_INET6, addr, &in6_addr);
>   int err = netlink_add_addr(sock, dev, &in6_addr, sizeof(in6_addr));
>   (void)err;
> }
>
> #define DEV_IPV4 "172.20.20.%d"
> #define DEV_IPV6 "fe80::%02hx"
> #define DEV_MAC 0x00aaaaaaaaaa
> static void initialize_netdevices(void)
> {
>   char netdevsim[16];
>   sprintf(netdevsim, "netdevsim%d", (int)procid);
>   struct {
>     const char* type;
>     const char* dev;
>   } devtypes[] = {
>       {"ip6gretap", "ip6gretap0"}, {"bridge", "bridge0"},
>       {"vcan", "vcan0"},           {"bond", "bond0"},
>       {"team", "team0"},           {"dummy", "dummy0"},
>       {"nlmon", "nlmon0"},         {"caif", "caif0"},
>       {"batadv", "batadv0"},       {"vxcan", "vxcan1"},
>       {"netdevsim", netdevsim},    {"veth", 0},
>   };
>   const char* devmasters[] = {"bridge", "bond", "team"};
>   struct {
>     const char* name;
>     int macsize;
>     bool noipv6;
>   } devices[] = {
>       {"lo", ETH_ALEN},
>       {"sit0", 0},
>       {"bridge0", ETH_ALEN},
>       {"vcan0", 0, true},
>       {"tunl0", 0},
>       {"gre0", 0},
>       {"gretap0", ETH_ALEN},
>       {"ip_vti0", 0},
>       {"ip6_vti0", 0},
>       {"ip6tnl0", 0},
>       {"ip6gre0", 0},
>       {"ip6gretap0", ETH_ALEN},
>       {"erspan0", ETH_ALEN},
>       {"bond0", ETH_ALEN},
>       {"veth0", ETH_ALEN},
>       {"veth1", ETH_ALEN},
>       {"team0", ETH_ALEN},
>       {"veth0_to_bridge", ETH_ALEN},
>       {"veth1_to_bridge", ETH_ALEN},
>       {"veth0_to_bond", ETH_ALEN},
>       {"veth1_to_bond", ETH_ALEN},
>       {"veth0_to_team", ETH_ALEN},
>       {"veth1_to_team", ETH_ALEN},
>       {"veth0_to_hsr", ETH_ALEN},
>       {"veth1_to_hsr", ETH_ALEN},
>       {"hsr0", 0},
>       {"dummy0", ETH_ALEN},
>       {"nlmon0", 0},
>       {"vxcan1", 0, true},
>       {"caif0", ETH_ALEN},
>       {"batadv0", ETH_ALEN},
>       {netdevsim, ETH_ALEN},
>   };
>   int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
>   if (sock == -1)
>     exit(1);
>   unsigned i;
>   for (i = 0; i < sizeof(devtypes) / sizeof(devtypes[0]); i++)
>     netlink_add_device(sock, devtypes[i].type, devtypes[i].dev);
>   for (i = 0; i < sizeof(devmasters) / (sizeof(devmasters[0])); i++) {
>     char master[32], slave0[32], veth0[32], slave1[32], veth1[32];
>     sprintf(slave0, "%s_slave_0", devmasters[i]);
>     sprintf(veth0, "veth0_to_%s", devmasters[i]);
>     netlink_add_veth(sock, slave0, veth0);
>     sprintf(slave1, "%s_slave_1", devmasters[i]);
>     sprintf(veth1, "veth1_to_%s", devmasters[i]);
>     netlink_add_veth(sock, slave1, veth1);
>     sprintf(master, "%s0", devmasters[i]);
>     netlink_device_change(sock, slave0, false, master, 0, 0);
>     netlink_device_change(sock, slave1, false, master, 0, 0);
>   }
>   netlink_device_change(sock, "bridge_slave_0", true, 0, 0, 0);
>   netlink_device_change(sock, "bridge_slave_1", true, 0, 0, 0);
>   netlink_add_veth(sock, "hsr_slave_0", "veth0_to_hsr");
>   netlink_add_veth(sock, "hsr_slave_1", "veth1_to_hsr");
>   netlink_add_hsr(sock, "hsr0", "hsr_slave_0", "hsr_slave_1");
>   netlink_device_change(sock, "hsr_slave_0", true, 0, 0, 0);
>   netlink_device_change(sock, "hsr_slave_1", true, 0, 0, 0);
>   for (i = 0; i < sizeof(devices) / (sizeof(devices[0])); i++) {
>     char addr[32];
>     sprintf(addr, DEV_IPV4, i + 10);
>     netlink_add_addr4(sock, devices[i].name, addr);
>     if (!devices[i].noipv6) {
>       sprintf(addr, DEV_IPV6, i + 10);
>       netlink_add_addr6(sock, devices[i].name, addr);
>     }
>     uint64_t macaddr = DEV_MAC + ((i + 10ull) << 40);
>     netlink_device_change(sock, devices[i].name, true, 0, &macaddr,
>                           devices[i].macsize);
>   }
>   close(sock);
> }
> static void initialize_netdevices_init(void)
> {
>   int sock = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
>   if (sock == -1)
>     exit(1);
>   struct {
>     const char* type;
>     int macsize;
>     bool noipv6;
>     bool noup;
>   } devtypes[] = {
>       {"nr", 7, true}, {"rose", 5, true, true},
>   };
>   unsigned i;
>   for (i = 0; i < sizeof(devtypes) / sizeof(devtypes[0]); i++) {
>     char dev[32], addr[32];
>     sprintf(dev, "%s%d", devtypes[i].type, (int)procid);
>     sprintf(addr, "172.30.%d.%d", i, (int)procid + 1);
>     netlink_add_addr4(sock, dev, addr);
>     if (!devtypes[i].noipv6) {
>       sprintf(addr, "fe88::%02hx:%02hx", i, (int)procid + 1);
>       netlink_add_addr6(sock, dev, addr);
>     }
>     int macsize = devtypes[i].macsize;
>     uint64_t macaddr = 0xbbbbbb +
>                        ((unsigned long long)i << (8 * (macsize - 2))) +
>                        (procid << (8 * (macsize - 1)));
>     netlink_device_change(sock, dev, !devtypes[i].noup, 0, &macaddr,
> macsize);
>   }
>   close(sock);
> }
>
> static void setup_common()
> {
>   if (mount(0, "/sys/fs/fuse/connections", "fusectl", 0, 0)) {
>   }
> }
>
> static void loop();
>
> static void sandbox_common()
> {
>   prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
>   setpgrp();
>   setsid();
>   struct rlimit rlim;
>   rlim.rlim_cur = rlim.rlim_max = 200 << 20;
>   setrlimit(RLIMIT_AS, &rlim);
>   rlim.rlim_cur = rlim.rlim_max = 32 << 20;
>   setrlimit(RLIMIT_MEMLOCK, &rlim);
>   rlim.rlim_cur = rlim.rlim_max = 136 << 20;
>   setrlimit(RLIMIT_FSIZE, &rlim);
>   rlim.rlim_cur = rlim.rlim_max = 1 << 20;
>   setrlimit(RLIMIT_STACK, &rlim);
>   rlim.rlim_cur = rlim.rlim_max = 0;
>   setrlimit(RLIMIT_CORE, &rlim);
>   rlim.rlim_cur = rlim.rlim_max = 256;
>   setrlimit(RLIMIT_NOFILE, &rlim);
>   if (unshare(CLONE_NEWNS)) {
>   }
>   if (unshare(CLONE_NEWIPC)) {
>   }
>   if (unshare(0x02000000)) {
>   }
>   if (unshare(CLONE_NEWUTS)) {
>   }
>   if (unshare(CLONE_SYSVSEM)) {
>   }
>   typedef struct {
>     const char* name;
>     const char* value;
>   } sysctl_t;
>   static const sysctl_t sysctls[] = {
>       {"/proc/sys/kernel/shmmax", "16777216"},
>       {"/proc/sys/kernel/shmall", "536870912"},
>       {"/proc/sys/kernel/shmmni", "1024"},
>       {"/proc/sys/kernel/msgmax", "8192"},
>       {"/proc/sys/kernel/msgmni", "1024"},
>       {"/proc/sys/kernel/msgmnb", "1024"},
>       {"/proc/sys/kernel/sem", "1024 1048576 500 1024"},
>   };
>   unsigned i;
>   for (i = 0; i < sizeof(sysctls) / sizeof(sysctls[0]); i++)
>     write_file(sysctls[i].name, sysctls[i].value);
> }
>
> int wait_for_loop(int pid)
> {
>   if (pid < 0)
>     exit(1);
>   int status = 0;
>   while (waitpid(-1, &status, __WALL) != pid) {
>   }
>   return WEXITSTATUS(status);
> }
>
> static int do_sandbox_none(void)
> {
>   if (unshare(CLONE_NEWPID)) {
>   }
>   int pid = fork();
>   if (pid != 0)
>     return wait_for_loop(pid);
>   setup_common();
>   sandbox_common();
>   initialize_netdevices_init();
>   if (unshare(CLONE_NEWNET)) {
>   }
>   initialize_netdevices();
>   loop();
>   exit(1);
> }
>
> #define FS_IOC_SETFLAGS _IOW('f', 2, long)
> static void remove_dir(const char* dir)
> {
>   DIR* dp;
>   struct dirent* ep;
>   int iter = 0;
> retry:
>   while (umount2(dir, MNT_DETACH) == 0) {
>   }
>   dp = opendir(dir);
>   if (dp == NULL) {
>     if (errno == EMFILE) {
>       exit(1);
>     }
>     exit(1);
>   }
>   while ((ep = readdir(dp))) {
>     if (strcmp(ep->d_name, ".") == 0 || strcmp(ep->d_name, "..") == 0)
>       continue;
>     char filename[FILENAME_MAX];
>     snprintf(filename, sizeof(filename), "%s/%s", dir, ep->d_name);
>     while (umount2(filename, MNT_DETACH) == 0) {
>     }
>     struct stat st;
>     if (lstat(filename, &st))
>       exit(1);
>     if (S_ISDIR(st.st_mode)) {
>       remove_dir(filename);
>       continue;
>     }
>     int i;
>     for (i = 0;; i++) {
>       if (unlink(filename) == 0)
>         break;
>       if (errno == EPERM) {
>         int fd = open(filename, O_RDONLY);
>         if (fd != -1) {
>           long flags = 0;
>           if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0)
>             close(fd);
>           continue;
>         }
>       }
>       if (errno == EROFS) {
>         break;
>       }
>       if (errno != EBUSY || i > 100)
>         exit(1);
>       if (umount2(filename, MNT_DETACH))
>         exit(1);
>     }
>   }
>   closedir(dp);
>   int i;
>   for (i = 0;; i++) {
>     if (rmdir(dir) == 0)
>       break;
>     if (i < 100) {
>       if (errno == EPERM) {
>         int fd = open(dir, O_RDONLY);
>         if (fd != -1) {
>           long flags = 0;
>           if (ioctl(fd, FS_IOC_SETFLAGS, &flags) == 0)
>             close(fd);
>           continue;
>         }
>       }
>       if (errno == EROFS) {
>         break;
>       }
>       if (errno == EBUSY) {
>         if (umount2(dir, MNT_DETACH))
>           exit(1);
>         continue;
>       }
>       if (errno == ENOTEMPTY) {
>         if (iter < 100) {
>           iter++;
>           goto retry;
>         }
>       }
>     }
>     exit(1);
>   }
> }
>
> static void kill_and_wait(int pid, int* status)
> {
>   kill(-pid, SIGKILL);
>   kill(pid, SIGKILL);
>   int i;
>   for (i = 0; i < 100; i++) {
>     if (waitpid(-1, status, WNOHANG | __WALL) == pid)
>       return;
>     usleep(1000);
>   }
>   DIR* dir = opendir("/sys/fs/fuse/connections");
>   if (dir) {
>     for (;;) {
>       struct dirent* ent = readdir(dir);
>       if (!ent)
>         break;
>       if (strcmp(ent->d_name, ".") == 0 || strcmp(ent->d_name, "..") == 0)
>         continue;
>       char abort[300];
>       snprintf(abort, sizeof(abort), "/sys/fs/fuse/connections/%s/abort",
>                ent->d_name);
>       int fd = open(abort, O_WRONLY);
>       if (fd == -1) {
>         continue;
>       }
>       if (write(fd, abort, 1) < 0) {
>       }
>       close(fd);
>     }
>     closedir(dir);
>   } else {
>   }
>   while (waitpid(-1, status, __WALL) != pid) {
>   }
> }
>
> #define SYZ_HAVE_SETUP_TEST 1
> static void setup_test()
> {
>   prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
>   setpgrp();
> }
>
> #define SYZ_HAVE_RESET_TEST 1
> static void reset_test()
> {
>   int fd;
>   for (fd = 3; fd < 30; fd++)
>     close(fd);
> }
>
> static void execute_one(void);
>
> #define WAIT_FLAGS __WALL
>
> static void loop(void)
> {
>   int iter;
>   for (iter = 0;; iter++) {
>     char cwdbuf[32];
>     sprintf(cwdbuf, "./%d", iter);
>     if (mkdir(cwdbuf, 0777))
>       exit(1);
>     int pid = fork();
>     if (pid < 0)
>       exit(1);
>     if (pid == 0) {
>       if (chdir(cwdbuf))
>         exit(1);
>       setup_test();
>       execute_one();
>       reset_test();
>       exit(0);
>     }
>     int status = 0;
>     uint64_t start = current_time_ms();
>     for (;;) {
>       if (waitpid(-1, &status, WNOHANG | WAIT_FLAGS) == pid)
>         break;
>       sleep_ms(1);
>       if (current_time_ms() - start < 5 * 1000)
>         continue;
>       kill_and_wait(pid, &status);
>       break;
>     }
>     remove_dir(cwdbuf);
>   }
> }
>
> void execute_one(void)
> {
>   syscall(__NR_unshare, 0x40000000);
> }
> int main(void)
> {
>   syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
>   for (procid = 0; procid < 8; procid++) {
>     if (fork() == 0) {
>       use_temporary_dir();
>       do_sandbox_none();
>     }
>   }
>   sleep(1000000);
>   return 0;
> }
>
>
> I reviewed kernel code and found a bug that
> net_drop_ns func doesn't call net_free func when refcount_dec_and_test's
> return value is zero.

Yes.  We don't call net_free when the reference count does not decrement
to zero.  The reference count is initialized to 1 a few lines above the
section of code in your patch so that should not be a problem.

> or
> when rv = down_read_killable(&pernet_ops_rwsem) < 0, it doesn't need to
> call refcount_dec_and_test.

It doesn't need to but it should be harmless.

> https://github.com/torvalds/linux/commit/5ba049a5cc8e24a1643df75bbf65b4efa070fa74#diff-9312644e2968a45510bacdd2b2872ad2
> (I can't reproduce this bug on v4.15 , and
> 1bdbe227492075d058e37cb3d400e6468d0095b5 with my patch. Because of the
> previous version of kernel doesn't have this bug.)
> This bug can lead to memory leak or DOS.
>
> I made a patch for this bug. (just revert to a before commit)

What am I missing?

The only thing I can see your patch doing is covering up a memory stomp
that has the effect of changing the value of net->passive.  I am not
really keen on hiding bugs of that kind.


> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index b02fb19df2cc..9de0ade14956 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -431,15 +431,18 @@ struct net *copy_net_ns(unsigned long flags,
>         get_user_ns(user_ns);
>
>         rv = down_read_killable(&pernet_ops_rwsem);
> -       if (rv < 0)
> -               goto put_userns;
> +       if (rv < 0){
> +        net_free(net);
> +        dec_net_namespaces(ucounts);
> +        put_user_ns(user_ns);
> +        return ERR_PTR(rv);
> +    }
>
>         rv = setup_net(net, user_ns);
>
>         up_read(&pernet_ops_rwsem);
>
>         if (rv < 0) {
> -put_userns:
>                 put_user_ns(user_ns);
>                 net_drop_ns(net);
>  dec_ucounts:
>
> and, sorry for my encrypted mails.

Eric