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Message-ID: <CANn89iJUHnzPa1EBD=eTK7J0R3XqHW=kqXcaCF0MbEzsBO+SEA@mail.gmail.com> Date: Wed, 12 Oct 2022 07:38:57 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, syzbot <syzkaller@...glegroups.com>, Tom Herbert <tom@...bertland.com> Subject: Re: [PATCH net] kcm: avoid potential race in kcm_tx_work On Wed, Oct 12, 2022 at 7:00 AM Dmitry Vyukov <dvyukov@...gle.com> wrote: > > On Wed, 12 Oct 2022 at 15:34, 'Eric Dumazet' via syzkaller > <syzkaller@...glegroups.com> wrote: > > > > 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. > > Does it make sense to add some lockdep annotations to sock_orphan() > and maybe some other similar functions to catch such cases earlier? I thought about that, but this seems net-next material. > > > > [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@...glegroups.com> > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > > Cc: Tom Herbert <tom@...bertland.com> > > --- > > 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 1215c863e1c410fa9ba5b9c3706152decfb3ebac..27725464ec08fe2b5f2e86202636cbc895568098 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. > > -- > > 2.38.0.rc1.362.ged0d419d3c-goog > > > > -- > > You received this message because you are subscribed to the Google Groups "syzkaller" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller+unsubscribe@...glegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller/20221012133412.519394-1-edumazet%40google.com.
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