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

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Date: Fri, 19 Apr 2024 17:36:13 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <rao.shoaib@...cle.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<kuniyu@...zon.com>, <netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH net] af_unix: Read with MSG_PEEK loops if the first unread byte is OOB

From: Rao Shoaib <rao.shoaib@...cle.com>
Date: Fri, 19 Apr 2024 04:46:32 +0000
> 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'
> 
> Fixes: 314001f0bf92 ("af_unix: Add OOB support")
> Signed-off-by: Rao Shoaib <Rao.Shoaib@...cle.com>
> ---
>  net/unix/af_unix.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 9a6ad5974dff..8928f1f496f4 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2658,19 +2658,20 @@ 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)) {

The patch does not apply cleanly on net.git probably because tab was
replaced by spaces ?

Could you check your mail client config and repost v2 to make patchwork
happy ?

https://patchwork.kernel.org/project/netdevbpf/patch/CH3PR10MB683386BD63824096BF86BA9DEF0D2@CH3PR10MB6833.namprd10.prod.outlook.com/



> -                               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);
> +                               if (!sock_flag(sk, SOCK_URGINLINE))

This can be `else if` to avoid another nesting here.


> +                                       skb = skb_peek_next(skb, &sk->sk_receive_queue);
>                         }
>                 }
>         }
> @@ -2747,9 +2748,11 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
>  #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
>                 if (skb) {
>                         skb = manage_oob(skb, sk, flags, copied);
> -                       if (!skb && copied) {
> +                       if (!skb) {
>                                 unix_state_unlock(sk);
> -                               break;
> +                               if (copied || (flags & MSG_PEEK))
> +                                       break;
> +                               goto redo;
>                         }
>                 }
>  #endif
> -- 
> 2.39.3