[PATCH net] kcm: avoid potential race in kcm_tx_work

[PATCH net] kcm: avoid potential race in kcm_tx_work

[Eric Dumazet]

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>
---
 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

Re: [PATCH net] kcm: avoid potential race in kcm_tx_work

[Dmitry Vyukov]

On Wed, 12 Oct 2022 at 15:34, 'Eric Dumazet' via syzkaller
<syzkaller@googlegroups.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?


> [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>
> ---
>  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
>
> --
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Re: [PATCH net] kcm: avoid potential race in kcm_tx_work

[Eric Dumazet]

On Wed, Oct 12, 2022 at 7:00 AM Dmitry Vyukov <dvyukov@google.com> wrote:
>
> On Wed, 12 Oct 2022 at 15:34, 'Eric Dumazet' via syzkaller
> <syzkaller@googlegroups.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@googlegroups.com>
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: Tom Herbert <tom@herbertland.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@googlegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller/20221012133412.519394-1-edumazet%40google.com.

Re: [PATCH net] kcm: avoid potential race in kcm_tx_work

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 12 Oct 2022 13:34:12 +0000 you 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);
> 	}
> 
> [...]

Here is the summary with links:
  - [net] kcm: avoid potential race in kcm_tx_work
    https://git.kernel.org/netdev/net/c/ec7eede369fe

You are awesome, thank you!
-- 
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