This is a note to let you know that I've just added the patch titled
af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
af_unix-call-kfree_skb-for-dead-unix_-sk-oob_skb-in-.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3c06850c389d1f6caf044bf3d95f8b47f9b2a987
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date: Sat Feb 3 10:31:49 2024 -0800
af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.
[ Upstream commit 1279f9d9dec2d7462823a18c29ad61359e0a007d ]
syzbot reported a warning [0] in __unix_gc() with a repro, which
creates a socketpair and sends one socket's fd to itself using the
peer.
socketpair(AF_UNIX, SOCK_STREAM, 0, [3, 4]) = 0
sendmsg(4, {msg_name=NULL, msg_namelen=0, msg_iov=[{iov_base="\360", iov_len=1}],
msg_iovlen=1, msg_control=[{cmsg_len=20, cmsg_level=SOL_SOCKET,
cmsg_type=SCM_RIGHTS, cmsg_data=[3]}],
msg_controllen=24, msg_flags=0}, MSG_OOB|MSG_PROBE|MSG_DONTWAIT|MSG_ZEROCOPY) = 1
This forms a self-cyclic reference that GC should finally untangle
but does not due to lack of MSG_OOB handling, resulting in memory
leak.
Recently, commit 11498715f266 ("af_unix: Remove io_uring code for
GC.") removed io_uring's dead code in GC and revealed the problem.
The code was executed at the final stage of GC and unconditionally
moved all GC candidates from gc_candidates to gc_inflight_list.
That papered over the reported problem by always making the following
WARN_ON_ONCE(!list_empty(&gc_candidates)) false.
The problem has been there since commit 2aab4b969002 ("af_unix: fix
struct pid leaks in OOB support") added full scm support for MSG_OOB
while fixing another bug.
To fix this problem, we must call kfree_skb() for unix_sk(sk)->oob_skb
if the socket still exists in gc_candidates after purging collected skb.
Then, we need to set NULL to oob_skb before calling kfree_skb() because
it calls last fput() and triggers unix_release_sock(), where we call
duplicate kfree_skb(u->oob_skb) if not NULL.
Note that the leaked socket remained being linked to a global list, so
kmemleak also could not detect it. We need to check /proc/net/protocol
to notice the unfreed socket.
[0]:
WARNING: CPU: 0 PID: 2863 at net/unix/garbage.c:345 __unix_gc+0xc74/0xe80 net/unix/garbage.c:345
Modules linked in:
CPU: 0 PID: 2863 Comm: kworker/u4:11 Not tainted 6.8.0-rc1-syzkaller-00583-g1701940b1a02 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: events_unbound __unix_gc
RIP: 0010:__unix_gc+0xc74/0xe80 net/unix/garbage.c:345
Code: 8b 5c 24 50 e9 86 f8 ff ff e8 f8 e4 22 f8 31 d2 48 c7 c6 30 6a 69 89 4c 89 ef e8 97 ef ff ff e9 80 f9 ff ff e8 dd e4 22 f8 90 <0f> 0b 90 e9 7b fd ff ff 48 89 df e8 5c e7 7c f8 e9 d3 f8 ff ff e8
RSP: 0018:ffffc9000b03fba0 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffc9000b03fc10 RCX: ffffffff816c493e
RDX: ffff88802c02d940 RSI: ffffffff896982f3 RDI: ffffc9000b03fb30
RBP: ffffc9000b03fce0 R08: 0000000000000001 R09: fffff52001607f66
R10: 0000000000000003 R11: 0000000000000002 R12: dffffc0000000000
R13: ffffc9000b03fc10 R14: ffffc9000b03fc10 R15: 0000000000000001
FS: 0000000000000000(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005559c8677a60 CR3: 000000000d57a000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
process_one_work+0x889/0x15e0 kernel/workqueue.c:2633
process_scheduled_works kernel/workqueue.c:2706 [inline]
worker_thread+0x8b9/0x12a0 kernel/workqueue.c:2787
kthread+0x2c6/0x3b0 kernel/kthread.c:388
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:242
</TASK>
Reported-by: syzbot+fa3ef895554bdbfd1183@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=fa3ef895554bdbfd1183
Fixes: 2aab4b969002 ("af_unix: fix struct pid leaks in OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240203183149.63573-1-kuniyu@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index 2405f0f9af31..8f63f0b4bf01 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -314,6 +314,17 @@ void unix_gc(void)
/* Here we are. Hitlist is filled. Die. */
__skb_queue_purge(&hitlist);
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+ list_for_each_entry_safe(u, next, &gc_candidates, link) {
+ struct sk_buff *skb = u->oob_skb;
+
+ if (skb) {
+ u->oob_skb = NULL;
+ kfree_skb(skb);
+ }
+ }
+#endif
+
spin_lock(&unix_gc_lock);
/* There could be io_uring registered files, just push them back to
