From: Eric Dumazet edumazet@google.com
commit ec7eede369fe5b0d085ac51fdbb95184f87bfc6c upstream.
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: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/kcm/kcmsock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -1844,10 +1844,10 @@ static int kcm_release(struct socket *so 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.