[PATCH 1/1] rxrpc: reject undecryptable rxkad response tickets

From: Yuqi Xu <redacted>

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 <redacted>
Reported-by: Juefei Pu <redacted>
Co-developed-by: Yuan Tan <redacted>
Signed-off-by: Yuan Tan <redacted>
Suggested-by: Xin Liu <redacted>
Tested-by: Ren Wei <redacted>
Signed-off-by: Yuqi Xu <redacted>
Signed-off-by: Ren Wei <redacted>
---
 net/rxrpc/rxkad.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/rxkad.c b/net/rxrpc/rxkad.c
index e923d6829008..0f79d694cb08 100644
--- a/net/rxrpc/rxkad.c
+++ b/net/rxrpc/rxkad.c

@@ -958,6 +958,7 @@ static int rxkad_decrypt_ticket(struct rxrpc_connection *conn,
 	struct in_addr addr;
 	unsigned int life;
 	time64_t issue, now;
+	int ret;
 	bool little_endian;
 	u8 *p, *q, *name, *end;
 

@@ -977,8 +978,11 @@ 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)
+		return rxrpc_abort_conn(conn, skb, RXKADBADTICKET, -EPROTO,
+					rxkad_abort_resp_tkt_short);
 
 	p = ticket;
 	end = p + ticket_len;

-- 
2.52.0