[PATCH 6.1.y] rxrpc: reject undecryptable rxkad response tickets

[Sasha Levin <sashal@kernel.org>]

From: Yuqi Xu <xuyuqiabc@gmail.com>

[ Upstream commit fe4447cd95623b1cfacc15f280aab73a6d7340b2 ]

rxkad_decrypt_ticket() decrypts the RXKAD response ticket and then
parses the buffer as plaintext without checking whether
crypto_skcipher_decrypt() succeeded.

A malformed RESPONSE can therefore use a non-block-aligned ticket
length, make the decrypt operation fail, and still drive the ticket
parser with attacker-controlled bytes.

Check the decrypt result and abort the connection with RXKADBADTICKET
when ticket decryption fails.

Fixes: 17926a79320a ("[AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both")
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Ren Wei <enjou1224z@gmail.com>
Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260408121252.2249051-12-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ adapted `rxrpc_abort_conn()` call to existing `goto other_error` error-handling pattern ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/rxrpc/rxkad.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index 78fa0524156f1..84a61fa18bc06 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c
@@ -1013,8 +1013,13 @@ static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
 	sg_init_one(&sg[0], ticket, ticket_len);
 	skcipher_request_set_callback(req, 0, NULL, NULL);
 	skcipher_request_set_crypt(req, sg, sg, ticket_len, iv.x);
-	crypto_skcipher_decrypt(req);
+	ret = crypto_skcipher_decrypt(req);
 	skcipher_request_free(req);
+	if (ret < 0) {
+		abort_code = RXKADBADTICKET;
+		ret = -EPROTO;
+		goto other_error;
+	}
 
 	p = ticket;
 	end = p + ticket_len;
-- 
2.53.0