FAILED: patch "[PATCH] rxrpc: serialize kernel accept preallocation with socket" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x dc175389b18c29a5303ee83169ec653adfae3e17
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072054-disk-reassign-c317@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dc175389b18c29a5303ee83169ec653adfae3e17 Mon Sep 17 00:00:00 2001
From: Li Daming <[email protected]>
Date: Tue, 9 Jun 2026 15:09:09 +0100
Subject: [PATCH] rxrpc: serialize kernel accept preallocation with socket
teardown

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.

index ee2d1319e69a..47824120f1da 100644
@@ -471,13 +471,26 @@ int rxrpc_kernel_charge_accept(struct socket *sock, rxrpc_notify_rx_t notify_rx,
 			       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;
 
-	if (sock->sk->sk_state == RXRPC_CLOSE)
-		return -ESHUTDOWN;
+	sk = sock->sk;
+	rx = rxrpc_sk(sk);
 
-	return rxrpc_service_prealloc_one(rx, b, notify_rx, user_call_ID,
-					  gfp, debug_id);
+	lock_sock(sk);
+	if (sk->sk_state != RXRPC_SERVER_LISTENING || !rx->backlog) {
+		ret = -ESHUTDOWN;
+		goto out;
+	}
+
+	b = rx->backlog;
+	ret = rxrpc_service_prealloc_one(rx, b, notify_rx, user_call_ID,
+					 gfp, debug_id);
+
+out:
+	release_sock(sk);
+	return ret;
 }
 EXPORT_SYMBOL(rxrpc_kernel_charge_accept);

From: Li Daming <[email protected]>

[ 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.

---
 net/rxrpc/call_accept.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

index 658b592e58e058..4a1e5d7a07262c 100644
@@ -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