Re: [PATCH net] net: Return error from sk_stream_wait_connect() if sk_wait_event() fails

Kuniyuki Iwashima
2023-12-14T13:46:46Z

From: Shigeru Yoshida <syoshida@redhat.com>
Date: Thu, 14 Dec 2023 22:31:06 +0900 (JST)
> On Thu, 14 Dec 2023 17:46:22 +0900, Kuniyuki Iwashima wrote:
> > From: Shigeru Yoshida <syoshida@redhat.com>
> > Date: Thu, 14 Dec 2023 14:09:22 +0900
> >> The following NULL pointer dereference issue occurred:
> >>
> >> BUG: kernel NULL pointer dereference, address: 0000000000000000
> >> <...>
> >> RIP: 0010:ccid_hc_tx_send_packet net/dccp/ccid.h:166 [inline]
> >> RIP: 0010:dccp_write_xmit+0x49/0x140 net/dccp/output.c:356
> >> <...>
> >> Call Trace:
> >> <TASK>
> >> dccp_sendmsg+0x642/0x7e0 net/dccp/proto.c:801
> >> inet_sendmsg+0x63/0x90 net/ipv4/af_inet.c:846
> >> sock_sendmsg_nosec net/socket.c:730 [inline]
> >> __sock_sendmsg+0x83/0xe0 net/socket.c:745
> >> ____sys_sendmsg+0x443/0x510 net/socket.c:2558
> >> ___sys_sendmsg+0xe5/0x150 net/socket.c:2612
> >> __sys_sendmsg+0xa6/0x120 net/socket.c:2641
> >> __do_sys_sendmsg net/socket.c:2650 [inline]
> >> __se_sys_sendmsg net/socket.c:2648 [inline]
> >> __x64_sys_sendmsg+0x45/0x50 net/socket.c:2648
> >> do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> >> do_syscall_64+0x43/0x110 arch/x86/entry/common.c:82
> >> entry_SYSCALL_64_after_hwframe+0x63/0x6b
> >>
> >> sk_wait_event() returns an error (-EPIPE) if disconnect() is called on the
> >> socket waiting for the event. However, sk_stream_wait_connect() returns
> >> success, i.e. zero, even if sk_wait_event() returns -EPIPE, so a function
> >> that waits for a connection with sk_stream_wait_connect() may misbehave.
> >>
> >> In the case of the above DCCP issue, dccp_sendmsg() is waiting for the
> >> connection. If disconnect() is called in concurrently, the above issue
> >> occurs.
> >>
> >> This patch fixes the issue by returning error from sk_stream_wait_connect()
> >> if sk_wait_event() fails.
> >>
> >> Fixes: 419ce133ab92 ("tcp: allow again tcp_disconnect() when threads are waiting")
> >> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
> >
> > Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> >
> > I guess you picked this issue from syzbot's report.
> > https://lore.kernel.org/netdev/0000000000009e122006088a2b8d@google.com/
> >
> > If so, let's give a proper credit to syzbot and its authors:
> >
> > Reported-by: syzbot+c71bc336c5061153b502@syzkaller.appspotmail.com
>
> Hi Kuniyuki-san,
>
> Thank you very much for your review. I didn't notice the syzbot's
> report. Actually, I found this issue by running syzkaller on my
> machine.

Thanks for clarifying.

I'm also running syzkaller locally and used to add

Reported-by: syzbot <syzkaller@googlegroups.com>

But, it was confusing for syzbot's owners, and I got a mail from one of
the authors, Aleksandr Nogikh. Since then, if syzkaller found an issue
that was not on the syzbot dashboard, I have used

Reported-by: syzkaller <syzkaller@googlegroups.com>

. FWIW, here's Aleksandr's words from the mail.

---8<---
Maybe it would be just a little more clear if instead of
Reported-by: syzbot <syzkaller@googlegroups.com>
you'd write
Reported-by: syzkaller <syzkaller@googlegroups.com>
if the bug was found only by a local syzkaller instance, because
otherwise it implies that the bug was found by syzbot, which is not
really the case here :)
---8<---

>
> Now, I tested this patch with syzbot, and it looks good.
>
> Reported-and-tested-by: syzbot+c71bc336c5061153b502@syzkaller.appspotmail.com

This time, this tag is best.

Thanks!