[PATCH net] net: reuseport: avoid duplicate closed socket insertion

[Lin Jiapeng <ljp1205831794@gmail.com>]

Clearing SO_REUSEPORT on a TCP listener clears sk_reuseport but leaves
sk_reuseport_cb attached to its reuseport group. A subsequent listen()
does not put the socket back into the listening section because
inet_hash() checks sk_reuseport. However, inet_unhash() checks
sk_reuseport_cb and calls reuseport_stop_listen_sock().

With request migration enabled, reuseport_stop_listen_sock() ignores
whether __reuseport_detach_sock() actually removed the socket from the
listening section and unconditionally appends it to the closed section.
Repeated connect(AF_UNSPEC)/listen() cycles therefore insert the same
socket until num_closed_socks exceeds max_socks. The next insertion
writes before socks[], overlapping prog on x86-64 and leading to type
confusion when a reuseport program is attached or detached.

Only insert the socket into the closed section when it was actually
removed from the listening section. A socket that was not rehashed as a
listener is already represented in the closed section, so leaving it
there preserves request migration semantics and prevents duplicate
entries and the resulting negative array indices.

Fixes: 333bb73f620e1 ("tcp: Keep TCP_CLOSE sockets in the reuseport group.")
Reported-by: TencentOS Corvus AI <corvus@tencent.com>
Cc: stable@vger.kernel.org
Signed-off-by: Lin Jiapeng <jiapenglin@tencent.com>
---
 net/core/sock_reuseport.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
index fccbdd0430b0..775f446516c3 100644
--- a/net/core/sock_reuseport.c
+++ b/net/core/sock_reuseport.c
@@ -480,8 +480,8 @@ void reuseport_stop_listen_sock(struct sock *sk)
 			 */
 			bpf_sk_reuseport_detach(sk);
 
-			__reuseport_detach_sock(sk, reuse);
-			__reuseport_add_closed_sock(sk, reuse);
+			if (__reuseport_detach_sock(sk, reuse))
+				__reuseport_add_closed_sock(sk, reuse);
 
 			spin_unlock_bh(&reuseport_lock);
 			return;
-- 
2.55.0