[PATCH 6.1.y] rxrpc: serialize kernel accept preallocation with socket teardown

[Sasha Levin]

From: Li Daming <d4n.for.sec at gmail.com>

[ Upstream commit dc175389b18c29a5303ee83169ec653adfae3e17 ]

rxrpc_kernel_charge_accept() reads rx->backlog without any
socket/backlog synchronization and passes that raw pointer into
rxrpc_service_prealloc_one(). A concurrent rxrpc_discard_prealloc()
sets rx->backlog = NULL and frees the backlog rings, so a kernel
preallocation worker can keep using a freed struct rxrpc_backlog
while updating *_backlog_head/tail and array slots.

Serialize the state check and backlog lookup with the socket lock,
and reject kernel preallocation once teardown has disabled
listening or discarded the service backlog.

Fixes: 00e907127e6f ("rxrpc: Preallocate peers, conns and calls for incoming service requests")
Reported-by: Yuan Tan <yuantan098 at gmail.com>
Reported-by: Yifan Wu <yifanwucs at gmail.com>
Reported-by: Juefei Pu <tomapufckgml at gmail.com>
Reported-by: Xin Liu <bird at lzu.edu.cn>
Signed-off-by: Li Daming <d4n.for.sec at gmail.com>
Signed-off-by: Ren Wei <n05ec at lzu.edu.cn>
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Marc Dionne <marc.dionne at auristor.com>
cc: Jeffrey Altman <jaltman at auristor.com>
cc: Simon Horman <horms at kernel.org>
cc: linux-afs at lists.infradead.org
cc: stable at kernel.org
Link: https://patch.msgid.link/20260609140911.838677-6-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
[ kept 6.1's extra user_attach_call argument in the rxrpc_service_prealloc_one() call ]
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 net/rxrpc/call_accept.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c
index 658b592e58e058..4a1e5d7a07262c 100644
--- a/net/rxrpc/call_accept.c
+++ b/net/rxrpc/call_accept.c
@@ -481,14 +481,27 @@ int rxrpc_kernel_charge_accept(struct socket *sock,
 			       unsigned long user_call_ID, gfp_t gfp,
 			       unsigned int debug_id)
 {
-	struct rxrpc_sock *rx = rxrpc_sk(sock->sk);
-	struct rxrpc_backlog *b = rx->backlog;
+	struct rxrpc_backlog *b;
+	struct rxrpc_sock *rx;
+	struct sock *sk;
+	int ret;
+
+	sk = sock->sk;
+	rx = rxrpc_sk(sk);
+
+	lock_sock(sk);
+	if (sk->sk_state != RXRPC_SERVER_LISTENING || !rx->backlog) {
+		ret = -ESHUTDOWN;
+		goto out;
+	}
 
-	if (sock->sk->sk_state == RXRPC_CLOSE)
-		return -ESHUTDOWN;
+	b = rx->backlog;
+	ret = rxrpc_service_prealloc_one(rx, b, notify_rx,
+					 user_attach_call, user_call_ID,
+					 gfp, debug_id);
 
-	return rxrpc_service_prealloc_one(rx, b, notify_rx,
-					  user_attach_call, user_call_ID,
-					  gfp, debug_id);
+out:
+	release_sock(sk);
+	return ret;
 }
 EXPORT_SYMBOL(rxrpc_kernel_charge_accept);
-- 
2.53.0