Re: [PATCH] net: phonet: do not BUG_ON() in pn_socket_autobind() on failed bind

[Rémi Denis-Courmont]

Hi,

Le keskiviikkona 22. huhtikuuta 2026, 4.38.07 Itä-Euroopan kesäaika Morduan 
Zang a écrit :
> syzbot reported a kernel BUG triggered from pn_socket_sendmsg() via
> pn_socket_autobind():
> 
>   kernel BUG at net/phonet/socket.c:213!
>   RIP: 0010:pn_socket_autobind net/phonet/socket.c:213 [inline]
>   RIP: 0010:pn_socket_sendmsg+0x240/0x250 net/phonet/socket.c:421
>   Call Trace:
>    sock_sendmsg_nosec+0x112/0x150 net/socket.c:797
>    __sock_sendmsg net/socket.c:812 [inline]
>    __sys_sendto+0x402/0x590 net/socket.c:2280
>    ...
> 
> pn_socket_autobind() calls pn_socket_bind() with port 0 and, on
> -EINVAL, assumes the socket was already bound and asserts that the
> port is non-zero:
> 
>   err = pn_socket_bind(sock, ..., sizeof(struct sockaddr_pn));
>   if (err != -EINVAL)
>           return err;
>   BUG_ON(!pn_port(pn_sk(sock->sk)->sobject));
>   return 0; /* socket was already bound */
> 
> However pn_socket_bind() also returns -EINVAL when sk->sk_state is not
> TCP_CLOSE, even when the socket has never been bound and pn_port() is
> still 0.  In that case the BUG_ON() fires and panics the kernel from a
> user-triggerable path.
> 
> Treat the "bind returned -EINVAL but pn_port() is still 0" case as a
> regular error and propagate -EINVAL to the caller instead of crashing.
> Existing callers already translate a non-zero return from
> pn_socket_autobind() into -ENOBUFS/-EAGAIN, so returning -EINVAL here
> only changes behaviour from panic to a normal errno.
> 
> Fixes: ba113a94b750 ("Phonet: common socket glue")
> Reported-by: syzbot+706f5eb79044e686c794@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=706f5eb79044e686c794
> Signed-off-by: Morduan Zang <zhangdandan@xxxxxxxxxxxxx>
> Signed-off-by: zhanjun <zhanjun@xxxxxxxxxxxxx>
> ---
>  net/phonet/socket.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/net/phonet/socket.c b/net/phonet/socket.c
> index 4423d483c630..de9108adfe1c 100644
> --- a/net/phonet/socket.c
> +++ b/net/phonet/socket.c
> @@ -210,7 +210,15 @@ static int pn_socket_autobind(struct socket *sock)
>  			     sizeof(struct sockaddr_pn));
>  	if (err != -EINVAL)
>  		return err;
> -	BUG_ON(!pn_port(pn_sk(sock->sk)->sobject));
> +	/*
> +	 * pn_socket_bind() can return -EINVAL both when the socket is
> +	 * already bound (pn_port() != 0) and when sk_state != TCP_CLOSE
> +	 * without a prior bind.  Only the former is an "already bound"
> +	 * success for autobind; otherwise propagate -EINVAL instead of
> +	 * crashing the kernel.
> +	 */
> +	if (!pn_port(pn_sk(sock->sk)->sobject))
> +		return -EINVAL;

This could be written as just if (err != -EINVAL || unlikely(...)) return err;

>  	return 0; /* socket was already bound */
>  }


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