From 93c99f21db360957d49853e5666b5c147f593bda Mon Sep 17 00:00:00 2001
From: Kuniyuki Iwashima <kuniyu@amazon.com>
Date: Mon, 24 Jun 2024 18:36:38 -0700
Subject: [PATCH] af_unix: Don't stop recv(MSG_DONTWAIT) if consumed OOB skb is
at the head.
Let's say a socket send()s "hello" with MSG_OOB and "world" without flags,
>>> from socket import *
>>> c1, c2 = socketpair(AF_UNIX)
>>> c1.send(b'hello', MSG_OOB)
5
>>> c1.send(b'world')
5
and its peer recv()s "hell" and "o".
>>> c2.recv(10)
b'hell'
>>> c2.recv(1, MSG_OOB)
b'o'
Now the consumed OOB skb stays at the head of recvq to return a correct
value for ioctl(SIOCATMARK), which is broken now and fixed by a later
patch.
Then, if peer issues recv() with MSG_DONTWAIT, manage_oob() returns NULL,
so recv() ends up with -EAGAIN.
>>> c2.setblocking(False) # This causes -EAGAIN even with available data
>>> c2.recv(5)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
BlockingIOError: [Errno 11] Resource temporarily unavailable
However, next recv() will return the following available data, "world".
>>> c2.recv(5)
b'world'
When the consumed OOB skb is at the head of the queue, we need to fetch
the next skb to fix the weird behaviour.
Note that the issue does not happen without MSG_DONTWAIT because we can
retry after manage_oob().
This patch also adds a test case that covers the issue.
Without fix:
# RUN msg_oob.no_peek.ex_oob_break ...
# msg_oob.c:134:ex_oob_break:AF_UNIX :Resource temporarily unavailable
# msg_oob.c:135:ex_oob_break:Expected:ld
# msg_oob.c:137:ex_oob_break:Expected ret[0] (-1) == expected_len (2)
# ex_oob_break: Test terminated by assertion
# FAIL msg_oob.no_peek.ex_oob_break
not ok 8 msg_oob.no_peek.ex_oob_break
With fix:
# RUN msg_oob.no_peek.ex_oob_break ...
# OK msg_oob.no_peek.ex_oob_break
ok 8 msg_oob.no_peek.ex_oob_break
Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
net/unix/af_unix.c | 19 +++++++++++++++----
tools/testing/selftests/net/af_unix/msg_oob.c | 11 +++++++++++
2 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 2eaecf9d78a49..b0b97f8d0d098 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2614,12 +2614,23 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
struct unix_sock *u = unix_sk(sk);
if (!unix_skb_len(skb)) {
- if (!(flags & MSG_PEEK)) {
- skb_unlink(skb, &sk->sk_receive_queue);
- consume_skb(skb);
+ struct sk_buff *unlinked_skb = NULL;
+
+ spin_lock(&sk->sk_receive_queue.lock);
+
+ if (copied) {
+ skb = NULL;
+ } else if (flags & MSG_PEEK) {
+ skb = skb_peek_next(skb, &sk->sk_receive_queue);
+ } else {
+ unlinked_skb = skb;
+ skb = skb_peek_next(skb, &sk->sk_receive_queue);
+ __skb_unlink(unlinked_skb, &sk->sk_receive_queue);
}
- skb = NULL;
+ spin_unlock(&sk->sk_receive_queue.lock);
+
+ consume_skb(unlinked_skb);
} else {
struct sk_buff *unlinked_skb = NULL;
diff --git a/tools/testing/selftests/net/af_unix/msg_oob.c b/tools/testing/selftests/net/af_unix/msg_oob.c
index de8d1fcde8837..b5226ccec3ece 100644
--- a/tools/testing/selftests/net/af_unix/msg_oob.c
+++ b/tools/testing/selftests/net/af_unix/msg_oob.c
@@ -238,4 +238,15 @@ TEST_F(msg_oob, oob_break_drop)
recvpair("", -EINVAL, 1, MSG_OOB);
}
+TEST_F(msg_oob, ex_oob_break)
+{
+ sendpair("hello", 5, MSG_OOB);
+ sendpair("wor", 3, MSG_OOB);
+ sendpair("ld", 2, 0);
+
+ recvpair("hellowo", 7, 10, 0); /* Break at OOB but not at ex-OOB. */
+ recvpair("r", 1, 1, MSG_OOB);
+ recvpair("ld", 2, 2, 0);
+}
+
TEST_HARNESS_MAIN
--
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