diff mbox series

[net] net/af_unix: fix a data-race in unix_dgram_poll

Message ID 20210909000029.1751608-1-eric.dumazet@gmail.com
State New
Headers show
Series [net] net/af_unix: fix a data-race in unix_dgram_poll | expand

Commit Message

Eric Dumazet Sept. 9, 2021, midnight UTC 
From: Eric Dumazet <edumazet@google.com>

syzbot reported another data-race in af_unix [1]

Lets change __skb_insert() to use WRITE_ONCE() when changing
skb head qlen.

Also, change unix_dgram_poll() to use lockless version
of unix_recvq_full()

It is verry possible we can switch all/most unix_recvq_full()
to the lockless version, this will be done in a future kernel version.

[1] HEAD commit: 8596e589b787732c8346f0482919e83cc9362db1

BUG: KCSAN: data-race in skb_queue_tail / unix_dgram_poll

write to 0xffff88814eeb24e0 of 4 bytes by task 25815 on cpu 0:
 __skb_insert include/linux/skbuff.h:1938 [inline]
 __skb_queue_before include/linux/skbuff.h:2043 [inline]
 __skb_queue_tail include/linux/skbuff.h:2076 [inline]
 skb_queue_tail+0x80/0xa0 net/core/skbuff.c:3264
 unix_dgram_sendmsg+0xff2/0x1600 net/unix/af_unix.c:1850
 sock_sendmsg_nosec net/socket.c:703 [inline]
 sock_sendmsg net/socket.c:723 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2392
 ___sys_sendmsg net/socket.c:2446 [inline]
 __sys_sendmmsg+0x315/0x4b0 net/socket.c:2532
 __do_sys_sendmmsg net/socket.c:2561 [inline]
 __se_sys_sendmmsg net/socket.c:2558 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2558
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814eeb24e0 of 4 bytes by task 25834 on cpu 1:
 skb_queue_len include/linux/skbuff.h:1869 [inline]
 unix_recvq_full net/unix/af_unix.c:194 [inline]
 unix_dgram_poll+0x2bc/0x3e0 net/unix/af_unix.c:2777
 sock_poll+0x23e/0x260 net/socket.c:1288
 vfs_poll include/linux/poll.h:90 [inline]
 ep_item_poll fs/eventpoll.c:846 [inline]
 ep_send_events fs/eventpoll.c:1683 [inline]
 ep_poll fs/eventpoll.c:1798 [inline]
 do_epoll_wait+0x6ad/0xf00 fs/eventpoll.c:2226
 __do_sys_epoll_wait fs/eventpoll.c:2238 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2233 [inline]
 __x64_sys_epoll_wait+0xf6/0x120 fs/eventpoll.c:2233
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000001b -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 25834 Comm: syz-executor.1 Tainted: G        W         5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Fixes: 86b18aaa2b5b ("skbuff: fix a data race in skb_queue_len()")
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/skbuff.h | 2 +-
 net/unix/af_unix.c     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Sept. 9, 2021, 10 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Wed,  8 Sep 2021 17:00:29 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>

> 

> syzbot reported another data-race in af_unix [1]

> 

> Lets change __skb_insert() to use WRITE_ONCE() when changing

> skb head qlen.

> 

> [...]


Here is the summary with links:
  - [net] net/af_unix: fix a data-race in unix_dgram_poll
    https://git.kernel.org/netdev/net/c/04f08eb44b50

You are awesome, thank you!
--
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diff mbox series

Patch

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6bdb0db3e8258ad2745705a9b046eb1c93e05840..841e2f0f5240ba9e210bb9a3fc1cbedc2162b2a8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1940,7 +1940,7 @@  static inline void __skb_insert(struct sk_buff *newsk,
 	WRITE_ONCE(newsk->prev, prev);
 	WRITE_ONCE(next->prev, newsk);
 	WRITE_ONCE(prev->next, newsk);
-	list->qlen++;
+	WRITE_ONCE(list->qlen, list->qlen + 1);
 }
 
 static inline void __skb_queue_splice(const struct sk_buff_head *list,
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index eb47b9de23809ac9216aae46c2fb1eae4543c890..92345c9bb60cc3b469e7cf50effe122b81c7bb89 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -3073,7 +3073,7 @@  static __poll_t unix_dgram_poll(struct file *file, struct socket *sock,
 
 		other = unix_peer(sk);
 		if (other && unix_peer(other) != sk &&
-		    unix_recvq_full(other) &&
+		    unix_recvq_full_lockless(other) &&
 		    unix_dgram_peer_wake_me(sk, other))
 			writable = 0;