netdev - [PATCH net] udp: fix race between close() and udp

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Message-Id: <2c54e352442c700440158d104c2bbc1ccbdf4ddf.1623232095.git.pabeni@redhat.com>
Date:   Wed,  9 Jun 2021 11:49:01 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Kaustubh Pandey <kapandey@...eaurora.org>,
        David Ahern <dsa@...ulusnetworks.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net] udp: fix race between close() and udp_abort()

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@...eaurora.org>
Fixes: 5d77dca82839 ("net: diag: support SOCK_DESTROY for UDP sockets")
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 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 055fceb18bea..bf98a87ac6e6 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2607,6 +2607,9 @@ 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)) {
@@ -2857,10 +2860,17 @@ 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 199b080d418a..3fcd86f4dfdc 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1598,6 +1598,9 @@ 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);
 
-- 
2.26.3