[PATCH 6.6.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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/trace/events/rxrpc.h |  2 ++
 net/rxrpc/conn_event.c       | 29 ++++++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 6965099dda89f..e8a5beca79cff 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -145,12 +145,14 @@
 	EM(rxrpc_skb_put_jumbo_subpacket,	"PUT jumbo-sub") \
 	EM(rxrpc_skb_put_last_nack,		"PUT last-nack") \
 	EM(rxrpc_skb_put_purge,			"PUT purge    ") \
+	EM(rxrpc_skb_put_response_copy,		"PUT resp-cpy ") \
 	EM(rxrpc_skb_put_rotate,		"PUT rotate   ") \
 	EM(rxrpc_skb_put_unknown,		"PUT unknown  ") \
 	EM(rxrpc_skb_see_conn_work,		"SEE conn-work") \
 	EM(rxrpc_skb_see_recvmsg,		"SEE recvmsg  ") \
 	EM(rxrpc_skb_see_reject,		"SEE reject   ") \
 	EM(rxrpc_skb_see_rotate,		"SEE rotate   ") \
+	EM(rxrpc_skb_see_unshare_nomem,		"SEE unshar-nm") \
 	E_(rxrpc_skb_see_version,		"SEE version  ")
 
 #define rxrpc_local_traces \
diff --git a/net/rxrpc/conn_event.c b/net/rxrpc/conn_event.c
index 6ef2dc1aa8cc2..6d7b064661d88 100644
--- a/net/rxrpc/conn_event.c
+++ b/net/rxrpc/conn_event.c
@@ -226,6 +226,33 @@ static void rxrpc_call_is_secure(struct rxrpc_call *call)
 		rxrpc_notify_socket(call);
 }
 
+static int rxrpc_verify_response(struct rxrpc_connection *conn,
+				 struct sk_buff *skb)
+{
+	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_new_unshared);
+			ret = conn->security->verify_response(conn, nskb);
+			rxrpc_free_skb(nskb, rxrpc_skb_put_response_copy);
+		} else {
+			/* OOM - Drop the packet. */
+			rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
+			ret = -ENOMEM;
+		}
+	} else {
+		ret = conn->security->verify_response(conn, skb);
+	}
+
+	return ret;
+}
+
 /*
  * connection-level Rx packet processor
  */
@@ -253,7 +280,7 @@ static int rxrpc_process_event(struct rxrpc_connection *conn,
 		}
 		spin_unlock(&conn->state_lock);
 
-		ret = conn->security->verify_response(conn, skb);
+		ret = rxrpc_verify_response(conn, skb);
 		if (ret < 0)
 			return ret;
 
-- 
2.53.0