[PATCH 6.1.y] rxrpc: Fix conn-level packet handling to unshare RESPONSE packets

[Sasha Levin <sashal@kernel.org>]

From: David Howells <dhowells@redhat.com>

[ Upstream commit 24481a7f573305706054c59e275371f8d0fe919f ]

The security operations that verify the RESPONSE packets decrypt bits of it
in place - however, the sk_buff may be shared with a packet sniffer, which
would lead to the sniffer seeing an apparently corrupt packet (actually
decrypted).

Fix this by handing a copy of the packet off to the specific security
handler if the packet was cloned.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Closes: https://sashiko.dev/#/patchset/20260408121252.2249051-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260422161438.2593376-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ adapted callback signature to include `_abort_code` ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/rxrpc/conn_event.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 5d91ef562ff78..09438850f9a5a 100644
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -285,6 +285,34 @@ static void rxrpc_call_is_secure(struct rxrpc_call *call)
 	}
 }
 
+static int rxrpc_verify_response(struct rxrpc_connection *conn,
+				 struct sk_buff *skb,
+				 u32 *_abort_code)
+{
+	int ret;
+
+	if (skb_cloned(skb)) {
+		/* Copy the packet if shared so that we can do in-place
+		 * decryption.
+		 */
+		struct sk_buff *nskb = skb_copy(skb, GFP_NOFS);
+
+		if (nskb) {
+			rxrpc_new_skb(nskb, rxrpc_skb_unshared);
+			ret = conn->security->verify_response(conn, nskb, _abort_code);
+			rxrpc_free_skb(nskb, rxrpc_skb_freed);
+		} else {
+			/* OOM - Drop the packet. */
+			rxrpc_see_skb(skb, rxrpc_skb_unshared_nomem);
+			ret = -ENOMEM;
+		}
+	} else {
+		ret = conn->security->verify_response(conn, skb, _abort_code);
+	}
+
+	return ret;
+}
+
 /*
  * connection-level Rx packet processor
  */
@@ -337,7 +365,7 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
 							    _abort_code);
 
 	case RXRPC_PACKET_TYPE_RESPONSE:
-		ret = conn->security->verify_response(conn, skb, _abort_code);
+		ret = rxrpc_verify_response(conn, skb, _abort_code);
 		if (ret < 0)
 			return ret;
 
-- 
2.53.0