[PATCH 3.16 158/366] net: af_packet: fix race in PACKET_{R|T}X_RING

Ben Hutchings
2018-10-14T15:25:41Z

From: Eric Dumazet <edumazet@google.com>

commit 5171b37d959641bbc619781caf62e61f7b940871 upstream.

In order to remove the race caught by syzbot [1], we need
to lock the socket before using po->tp_version as this could
change under us otherwise.

This means lock_sock() and release_sock() must be done by
packet_set_ring() callers.

[1] :
BUG: KMSAN: uninit-value in packet_set_ring+0x1254/0x3870 net/packet/af_packet.c:4249
CPU: 0 PID: 20195 Comm: syzkaller707632 Not tainted 4.16.0+ #83
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x185/0x1d0 lib/dump_stack.c:53
kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
__msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:676
packet_set_ring+0x1254/0x3870 net/packet/af_packet.c:4249
packet_setsockopt+0x12c6/0x5a90 net/packet/af_packet.c:3662
SYSC_setsockopt+0x4b8/0x570 net/socket.c:1849
SyS_setsockopt+0x76/0xa0 net/socket.c:1828
do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x449099
RSP: 002b:00007f42b5307ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 000000000070003c RCX: 0000000000449099
RDX: 0000000000000005 RSI: 0000000000000107 RDI: 0000000000000003
RBP: 0000000000700038 R08: 000000000000001c R09: 0000000000000000
R10: 00000000200000c0 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000080eecf R14: 00007f42b53089c0 R15: 0000000000000001

Local variable description: ----req_u@packet_setsockopt
Variable was created at:
packet_setsockopt+0x13f/0x5a90 net/packet/af_packet.c:3612
SYSC_setsockopt+0x4b8/0x570 net/socket.c:1849

Fixes: f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: PACKET_VNET_HDR is incompatible with
PACKET_{TX,RX}_RING; fix up the check for that as well]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2651,6 +2651,7 @@ static int packet_release(struct socket

packet_flush_mclist(sk);

+ lock_sock(sk);
if (po->rx_ring.pg_vec) {
memset(&req_u, 0, sizeof(req_u));
packet_set_ring(sk, &req_u, 1, 0);
@@ -2660,6 +2661,7 @@ static int packet_release(struct socket
memset(&req_u, 0, sizeof(req_u));
packet_set_ring(sk, &req_u, 1, 1);
}
+ release_sock(sk);

f = fanout_release(sk);

@@ -3295,6 +3297,7 @@ packet_setsockopt(struct socket *sock, i
union tpacket_req_u req_u;
int len;

+ lock_sock(sk);
switch (po->tp_version) {
case TPACKET_V1:
case TPACKET_V2:
@@ -3305,14 +3308,19 @@ packet_setsockopt(struct socket *sock, i
len = sizeof(req_u.req3);
break;
}
- if (optlen < len)
- return -EINVAL;
- if (pkt_sk(sk)->has_vnet_hdr)
- return -EINVAL;
- if (copy_from_user(&req_u.req, optval, len))
- return -EFAULT;
- return packet_set_ring(sk, &req_u, 0,
- optname == PACKET_TX_RING);
+ if (optlen < len) {
+ ret = -EINVAL;
+ } else if (pkt_sk(sk)->has_vnet_hdr) {
+ ret = -EINVAL;
+ } else {
+ if (copy_from_user(&req_u.req, optval, len))
+ ret = -EFAULT;
+ else
+ ret = packet_set_ring(sk, &req_u, 0,
+ optname == PACKET_TX_RING);
+ }
+ release_sock(sk);
+ return ret;
}
case PACKET_COPY_THRESH:
{
@@ -3820,7 +3828,6 @@ static int packet_set_ring(struct sock *
/* Added to avoid minimal code churn */
struct tpacket_req *req = &req_u->req;

- lock_sock(sk);
/* Opening a Tx-ring is NOT supported in TPACKET_V3 */
if (!closing && tx_ring && (po->tp_version > TPACKET_V2)) {
WARN(1, "Tx-ring is not supported.\n");
@@ -3956,7 +3963,6 @@ static int packet_set_ring(struct sock *
if (pg_vec)
free_pg_vec(pg_vec, order, req->tp_block_nr);
out:
- release_sock(sk);
return err;
}