From: Paolo Abeni <pabeni@redhat.com>
Date: Wed, 9 Jun 2021 09:49:01 +0000 (+0200)
Subject: udp: fix race between close() and udp_abort()
X-Git-Tag: v4.19.196~80
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2f73448041bd0682d4b552cfd314ace66107f1ad;p=thirdparty%2Fkernel%2Fstable.git

udp: fix race between close() and udp_abort()

[ Upstream commit a8b897c7bcd47f4147d066e22cc01d1026d7640e ]

Kaustubh reported and diagnosed a panic in udp_lib_lookup().
The root cause is udp_abort() racing with close(). Both
racing functions acquire the socket lock, but udp{v6}_destroy_sock()
release it before performing destructive actions.

We can't easily extend the socket lock scope to avoid the race,
instead use the SOCK_DEAD flag to prevent udp_abort from doing
any action when the critical race happens.

Diagnosed-and-tested-by: Kaustubh Pandey <kapandey@codeaurora.org>
Fixes: 5d77dca82839 ("net: diag: support SOCK_DESTROY for UDP sockets")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 110af0e7dc7b6..2ff9f774d4463 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2432,6 +2432,9 @@ void udp_destroy_sock(struct sock *sk)
 {
 	struct udp_sock *up = udp_sk(sk);
 	bool slow = lock_sock_fast(sk);
+
+	/* protects from races with udp_abort() */
+	sock_set_flag(sk, SOCK_DEAD);
 	udp_flush_pending_frames(sk);
 	unlock_sock_fast(sk, slow);
 	if (static_branch_unlikely(&udp_encap_needed_key) && up->encap_type) {
@@ -2673,10 +2676,17 @@ int udp_abort(struct sock *sk, int err)
 {
 	lock_sock(sk);
 
+	/* udp{v6}_destroy_sock() sets it under the sk lock, avoid racing
+	 * with close()
+	 */
+	if (sock_flag(sk, SOCK_DEAD))
+		goto out;
+
 	sk->sk_err = err;
 	sk->sk_error_report(sk);
 	__udp_disconnect(sk, 0);
 
+out:
 	release_sock(sk);
 
 	return 0;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 6799ad462be30..c4a76c6af205d 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1476,6 +1476,9 @@ void udpv6_destroy_sock(struct sock *sk)
 {
 	struct udp_sock *up = udp_sk(sk);
 	lock_sock(sk);
+
+	/* protects from races with udp_abort() */
+	sock_set_flag(sk, SOCK_DEAD);
 	udp_v6_flush_pending_frames(sk);
 	release_sock(sk);