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

[Kuniyuki Iwashima <kuniyu@amazon.com>]

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

Thanks!

> ---
>  net/core/stream.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/stream.c b/net/core/stream.c
> index 96fbcb9bbb30..b16dfa568a2d 100644
> --- a/net/core/stream.c
> +++ b/net/core/stream.c
> @@ -79,7 +79,7 @@ int sk_stream_wait_connect(struct sock *sk, long *timeo_p)
>  		remove_wait_queue(sk_sleep(sk), &wait);
>  		sk->sk_write_pending--;
>  	} while (!done);
> -	return 0;
> +	return done < 0 ? done : 0;
>  }
>  EXPORT_SYMBOL(sk_stream_wait_connect);
>  
> -- 
> 2.41.0
>