[PATCH 4.9 21/71] udp: fix race between close() and udp_abort()

Sasha Levin
2021-06-28T15:19:34Z

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 18a1a4890c5f..79249a44e4a3 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1998,6 +1998,9 @@ 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_key_false(&udp_encap_needed) && up->encap_type) {
@@ -2228,10 +2231,17 @@ 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 1ad84e18c03b..3a876a2fdd82 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1325,6 +1325,9 @@ 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