releases/5.4.128/udp-fix-race-between-close-and-udp_abort.patch

From 424f7927c1ed0c4a954fc03320368bd8d0e681d5 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Wed, 9 Jun 2021 11:49:01 +0200
Subject: udp: fix race between close() and udp_abort()

From: Paolo Abeni <pabeni@redhat.com>

[ 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>
---
 net/ipv4/udp.c | 10 ++++++++++
 net/ipv6/udp.c |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 24841a9e9966..4644f86c932f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2511,6 +2511,9 @@ 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)) {
@@ -2770,10 +2773,17 @@ 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 6762430280f5..3c94b81bb459 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1539,6 +1539,9 @@ 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);
 
-- 
2.30.2