[PATCH net v3] af_unix: Read with MSG_PEEK loops if the first unread byte is OOB

[Rao Shoaib <Rao.Shoaib@oracle.com>]

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@oracle.com>
---
 net/unix/af_unix.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 9a6ad5974dff..ed5f70735435 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2658,19 +2658,19 @@ 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);
 			}
 		}
 	}
@@ -2747,9 +2747,11 @@ 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