From ec7eede369fe5b0d085ac51fdbb95184f87bfc6c Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Wed, 12 Oct 2022 13:34:12 +0000
Subject: [PATCH] kcm: avoid potential race in kcm_tx_work
Git-commit: ec7eede369fe5b0d085ac51fdbb95184f87bfc6c
Patch-mainline: v6.1-rc1
References: bsc#1204355 CVE-2022-3521
syzbot found that kcm_tx_work() could crash [1] in:
/* Primarily for SOCK_SEQPACKET sockets */
if (likely(sk->sk_socket) &&
test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
<<*>> clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
sk->sk_write_space(sk);
}
I think the reason is that another thread might concurrently
run in kcm_release() and call sock_orphan(sk) while sk is not
locked. kcm_tx_work() find sk->sk_socket being NULL.
[1]
BUG: KASAN: null-ptr-deref in instrument_atomic_write include/linux/instrumented.h:86 [inline]
BUG: KASAN: null-ptr-deref in clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
BUG: KASAN: null-ptr-deref in kcm_tx_work+0xff/0x160 net/kcm/kcmsock.c:742
Write of size 8 at addr 0000000000000008 by task kworker/u4:3/53
CPU: 0 PID: 53 Comm: kworker/u4:3 Not tainted 5.19.0-rc3-next-20220621-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: kkcmd kcm_tx_work
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
kasan_report+0xbe/0x1f0 mm/kasan/report.c:495
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189
instrument_atomic_write include/linux/instrumented.h:86 [inline]
clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
kcm_tx_work+0xff/0x160 net/kcm/kcmsock.c:742
process_one_work+0x996/0x1610 kernel/workqueue.c:2289
worker_thread+0x665/0x1080 kernel/workqueue.c:2436
kthread+0x2e9/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:302
</TASK>
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Link: https://lore.kernel.org/r/20221012133412.519394-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Denis Kirjanov <dkirjanov@suse.de>
---
net/kcm/kcmsock.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 1215c863e1c4..27725464ec08 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -1838,10 +1838,10 @@ static int kcm_release(struct socket *sock)
kcm = kcm_sk(sk);
mux = kcm->mux;
+ lock_sock(sk);
sock_orphan(sk);
kfree_skb(kcm->seq_skb);
- lock_sock(sk);
/* Purge queue under lock to avoid race condition with tx_work trying
* to act when queue is nonempty. If tx_work runs after this point
* it will just return.
--
2.16.4