From 2acbbaadf7826621eee48e7e7e0ef2b25a048adb Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 8 Sep 2021 17:00:29 -0700
Subject: [PATCH] net/af_unix: fix a data-race in unix_dgram_poll
Git-commit: 04f08eb44b5011493d77b602fdec29ff0f5c6cd5
Patch-mainline: v5.15-rc2
References: git-fixes
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
include/linux/skbuff.h | 2 +-
net/unix/af_unix.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6c36dd6e5b7e..a6dc5f341f74 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1620,7 +1620,7 @@ 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 f59843a1f842..e146578b3f2a 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2747,7 +2747,7 @@ static unsigned int 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;
--
2.16.4