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@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>

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 15f5504..1307ad0 100644 (file)
--- 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 199b080..3fcd86f 100644 (file)
--- 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);