linux-kernel - [PATCH 2/2] phonet/pep: fix racy skb_queue

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Message-ID: <20240210125054.71391-2-remi@remlab.net>
Date: Sat, 10 Feb 2024 14:50:54 +0200
From: Rémi Denis-Courmont <remi@...lab.net>
To: courmisch@...il.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] phonet/pep: fix racy skb_queue_empty() use

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

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.

Signed-off-by: Rémi Denis-Courmont <courmisch@...il.com>
---
 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 faba31f2eff2..3dd5f52bc1b5 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