[PATCH 5.15 23/71] af_unix: Dont peek OOB data without MSG_OOB.

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>

[ Upstream commit 22dd70eb2c3d754862964377a75abafd3167346b ]

Currently, we can read OOB data without MSG_OOB by using MSG_PEEK
when OOB data is sitting on the front row, which is apparently
wrong.

  >>> from socket import *
  >>> c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
  >>> c1.send(b'a', MSG_OOB)
  1
  >>> c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
  b'a'

If manage_oob() is called when no data has been copied, we only
check if the socket enables SO_OOBINLINE or MSG_PEEK is not used.
Otherwise, the skb is returned as is.

However, here we should return NULL if MSG_PEEK is set and no data
has been copied.

Also, in such a case, we should not jump to the redo label because
we will be caught in the loop and hog the CPU until normal data
comes in.

Then, we need to handle skb == NULL case with the if-clause below
the manage_oob() block.

With this patch:

  >>> from socket import *
  >>> c1, c2 = socketpair(AF_UNIX, SOCK_STREAM)
  >>> c1.send(b'a', MSG_OOB)
  1
  >>> c2.recv(1, MSG_PEEK | MSG_DONTWAIT)
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  BlockingIOError: [Errno 11] Resource temporarily unavailable

Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240410171016.7621-3-kuniyu@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/unix/af_unix.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e2a2e22d210f6..f66f867049015 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2565,7 +2565,9 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 					WRITE_ONCE(u->oob_skb, NULL);
 					consume_skb(skb);
 				}
-			} else if (!(flags & MSG_PEEK)) {
+			} 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)))
@@ -2648,11 +2650,9 @@ 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) {
+			if (!skb && copied) {
 				unix_state_unlock(sk);
-				if (copied)
-					break;
-				goto redo;
+				break;
 			}
 		}
 #endif
-- 
2.43.0







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