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

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Message-ID: 
 <CH3PR10MB683386BD63824096BF86BA9DEF0D2@CH3PR10MB6833.namprd10.prod.outlook.com>
Date: Fri, 19 Apr 2024 04:46:32 +0000
From: Rao Shoaib <rao.shoaib@...cle.com>
To: "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni
	<pabeni@...hat.com>
CC: Kuniyuki Iwashima <kuniyu@...zon.com>,
        "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
Subject: [PATCH net] af_unix: Read with MSG_PEEK loops if the first unread
 byte is OOB

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)) {
-                               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))
+                                       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