[PATCH 6.8 023/158] af_unix: Dont peek OOB data without MSG_OOB.

Greg Kroah-Hartman
2024-04-23T21:41:02Z

From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ 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@amazon.com>
Link: https://lore.kernel.org/r/20240410171016.7621-3-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 fd931f3005cd8..9df15a7bc2569 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2602,7 +2602,9 @@ 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)))
@@ -2684,11 +2686,9 @@ 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