netdev - Re: [PATCH v5] af_unix: Read with MSG_PEEK loops if the first unread byte is OOB

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Date: Tue, 21 May 2024 13:11:52 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Rao Shoaib <Rao.Shoaib@...cle.com>, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org
Cc: kuniyu@...zon.com, netdev@...r.kernel.org
Subject: Re: [PATCH v5] af_unix: Read with MSG_PEEK loops if the first
 unread byte is OOB

On Thu, 2024-05-16 at 16:16 -0700, Rao Shoaib wrote:
> Read with MSG_PEEK flag loops if the first byte to read is an OOB byte.
> commit 22dd70eb2c3d ("af_unix: Don't peek OOB data without MSG_OOB.")
> addresses the loop issue but does not address the issue that no data
> beyond OOB byte can be read.
> 
> > > > from socket import *
> > > > c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
> > > > c1.send(b'a', MSG_OOB)
> 1
> > > > c1.send(b'b')
> 1
> > > > c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
> b'b'
> 
> > > > from socket import *
> > > > c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
> > > > c2.setsockopt(SOL_SOCKET, SO_OOBINLINE, 1)
> > > > c1.send(b'a', MSG_OOB)
> 1
> > > > c1.send(b'b')
> 1
> > > > c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
> b'a'
> > > > c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
> b'a'
> > > > c2.recv(1, MSG_DONTWAIT)
> b'a'
> > > > c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
> b'b'
> > > > 
> 
> Fixes: 314001f0bf92 ("af_unix: Add OOB support")
> Signed-off-by: Rao Shoaib <Rao.Shoaib@...cle.com>
> ---
>  net/unix/af_unix.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index fa906ec5e657..6e5ef44640ea 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2612,19 +2612,19 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
>  		if (skb == u->oob_skb) {
>  			if (copied) {
>  				skb = NULL;
> -			} else if (sock_flag(sk, SOCK_URGINLINE)) {
> -				if (!(flags & MSG_PEEK)) {
> +			} else if (!(flags & MSG_PEEK)) {
> +				if (sock_flag(sk, SOCK_URGINLINE)) {
>  					WRITE_ONCE(u->oob_skb, NULL);
>  					consume_skb(skb);
> +				} else {
> +					skb_unlink(skb, &sk->sk_receive_queue);
> +					WRITE_ONCE(u->oob_skb, NULL);
> +					if (!WARN_ON_ONCE(skb_unref(skb)))
> +						kfree_skb(skb);
> +					skb = skb_peek(&sk->sk_receive_queue);
>  				}
> -			} else if (flags & MSG_PEEK) {
> -				skb = NULL;
> -			} else {
> -				skb_unlink(skb, &sk->sk_receive_queue);
> -				WRITE_ONCE(u->oob_skb, NULL);
> -				if (!WARN_ON_ONCE(skb_unref(skb)))
> -					kfree_skb(skb);
> -				skb = skb_peek(&sk->sk_receive_queue);
> +			} else if (!sock_flag(sk, SOCK_URGINLINE)) {
> +				skb = skb_peek_next(skb, &sk->sk_receive_queue);
>  			}
>  		}
>  	}

Does not apply cleanly anymore after commit 9841991a446c ("af_unix:
Update unix_sk(sk)->oob_skb under sk_receive_queue lock."), please
rebase, thanks!

Paolo