[PATCH 6.6 283/299] phonet/pep: fix racy skb_queue_empty() use

Greg Kroah-Hartman
2024-02-27T14:00:02Z

From: Rémi Denis-Courmont <courmisch@gmail.com>

[ Upstream commit 7d2a894d7f487dcb894df023e9d3014cf5b93fe5 ]

The receive queues are protected by their respective spin-lock, not
the socket lock. This could lead to skb_peek() unexpectedly
returning NULL or a pointer to an already dequeued socket buffer.

Fixes: 9641458d3ec4 ("Phonet: Pipe End Point for Phonet Pipes protocol")
Signed-off-by: Rémi Denis-Courmont <courmisch@gmail.com>
Link: https://lore.kernel.org/r/20240218081214.4806-2-remi@remlab.net
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/phonet/pep.c | 41 ++++++++++++++++++++++++++++++++---------
1 file changed, 32 insertions(+), 9 deletions(-)

diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index faba31f2eff29..3dd5f52bc1b58 100644
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -917,6 +917,37 @@ static int pep_sock_enable(struct sock *sk, struct sockaddr *addr, int len)
return 0;
}

+static unsigned int pep_first_packet_length(struct sock *sk)
+{
+ struct pep_sock *pn = pep_sk(sk);
+ struct sk_buff_head *q;
+ struct sk_buff *skb;
+ unsigned int len = 0;
+ bool found = false;
+
+ if (sock_flag(sk, SOCK_URGINLINE)) {
+ q = &pn->ctrlreq_queue;
+ spin_lock_bh(&q->lock);
+ skb = skb_peek(q);
+ if (skb) {
+ len = skb->len;
+ found = true;
+ }
+ spin_unlock_bh(&q->lock);
+ }
+
+ if (likely(!found)) {
+ q = &sk->sk_receive_queue;
+ spin_lock_bh(&q->lock);
+ skb = skb_peek(q);
+ if (skb)
+ len = skb->len;
+ spin_unlock_bh(&q->lock);
+ }
+
+ return len;
+}
+
static int pep_ioctl(struct sock *sk, int cmd, int *karg)
{
struct pep_sock *pn = pep_sk(sk);
@@ -929,15 +960,7 @@ static int pep_ioctl(struct sock *sk, int cmd, int *karg)
break;
}

- lock_sock(sk);
- if (sock_flag(sk, SOCK_URGINLINE) &&
- !skb_queue_empty(&pn->ctrlreq_queue))
- *karg = skb_peek(&pn->ctrlreq_queue)->len;
- else if (!skb_queue_empty(&sk->sk_receive_queue))
- *karg = skb_peek(&sk->sk_receive_queue)->len;
- else
- *karg = 0;
- release_sock(sk);
+ *karg = pep_first_packet_length(sk);
ret = 0;
break;

--
2.43.0