[PATCH net v10 10/14] rxrpc: Fix RxGK key parser to check enctype is supported

[David Howells <dhowells@redhat.com>]

Fix the parser of RxGK keys supplied by userspace to check that the
specified encryption type is supported and check the key length.  Further,
since the checking function isn't necessarily available in CONFIG_RXGK=n,
make the RxGK key wrangling bits conditional.

Fixes: 0ca100ff4df6 ("rxrpc: Add YFS RxGK (GSSAPI) security class")
Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260824091645.415423-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Eric Dumazet <edumazet@google.com>
cc: "David S. Miller" <davem@davemloft.net>
cc: Jakub Kicinski <kuba@kernel.org>
cc: Paolo Abeni <pabeni@redhat.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@vger.kernel.org
---
 net/rxrpc/key.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index a0aa78d89289..dc1b3aa51bf3 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -129,6 +129,7 @@ static int rxrpc_preparse_xdr_rxkad(struct key_preparsed_payload *prep,
 	return 0;
 }
 
+#ifdef CONFIG_RXGK
 static u64 xdr_dec64(const __be32 *xdr)
 {
 	return (u64)ntohl(xdr[0]) << 32 | (u64)ntohl(xdr[1]);
@@ -166,12 +167,14 @@ static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
 				       size_t datalen,
 				       const __be32 *xdr, unsigned int toklen)
 {
+	const struct krb5_enctype *enc;
 	struct rxrpc_key_token *token, **pptoken;
 	time64_t expiry;
 	size_t plen;
 	const __be32 *ticket, *key;
 	s64 tmp;
 	size_t raw_keylen, raw_tktlen, keylen, tktlen;
+	int ret = -EKEYREJECTED;
 
 	_enter(",{%x,%x,%x,%x},%x",
 	       ntohl(xdr[0]), ntohl(xdr[1]), ntohl(xdr[2]), ntohl(xdr[3]),
@@ -229,6 +232,17 @@ static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
 	token->rxgk->key.data	= token->rxgk->_key;
 	token->rxgk->ticket.len = raw_tktlen;
 
+	/* Check the enctype is supported. */
+	enc = crypto_krb5_find_enctype(token->rxgk->enctype);
+	if (!enc) {
+		ret = -ENOPKG;
+		goto reject_token;
+	}
+	if (raw_keylen != enc->key_len) {
+		ret = -EKEYREJECTED;
+		goto reject_token;
+	}
+
 	if (token->rxgk->endtime != 0) {
 		expiry = rxrpc_s64_to_time64(token->rxgk->endtime);
 		if (expiry < 0)
@@ -280,12 +294,13 @@ static int rxrpc_preparse_xdr_yfs_rxgk(struct key_preparsed_payload *prep,
 	kfree(token->rxgk);
 	kfree(token);
 reject:
-	return -EKEYREJECTED;
+	return ret;
 expired:
 	kfree(token->rxgk);
 	kfree(token);
 	return -EKEYEXPIRED;
 }
+#endif /* CONFIG_RXGK */
 
 /*
  * attempt to parse the data as the XDR format
@@ -386,9 +401,11 @@ static int rxrpc_preparse_xdr(struct key_preparsed_payload *prep)
 		case RXRPC_SECURITY_RXKAD:
 			ret2 = rxrpc_preparse_xdr_rxkad(prep, datalen, token, toklen);
 			break;
+#ifdef CONFIG_RXGK
 		case RXRPC_SECURITY_YFS_RXGK:
 			ret2 = rxrpc_preparse_xdr_yfs_rxgk(prep, datalen, token, toklen);
 			break;
+#endif
 		default:
 			ret2 = -EPROTONOSUPPORT;
 			break;
@@ -556,10 +573,12 @@ static void rxrpc_free_token_list(struct rxrpc_key_token *token)
 		case RXRPC_SECURITY_RXKAD:
 			kfree(token->kad);
 			break;
+#ifdef CONFIG_RXGK
 		case RXRPC_SECURITY_YFS_RXGK:
 			kfree(token->rxgk->ticket.data);
 			kfree(token->rxgk);
 			break;
+#endif
 		default:
 			pr_err("Unknown token type %x on rxrpc key\n",
 			       token->security_index);
@@ -603,9 +622,11 @@ static void rxrpc_describe(const struct key *key, struct seq_file *m)
 		case RXRPC_SECURITY_RXKAD:
 			seq_puts(m, "ka");
 			break;
+#ifdef CONFIG_RXGK
 		case RXRPC_SECURITY_YFS_RXGK:
 			seq_puts(m, "ygk");
 			break;
+#endif
 		default: /* we have a ticket we can't encode */
 			seq_printf(m, "%u", token->security_index);
 			break;
@@ -770,12 +791,14 @@ static long rxrpc_read(const struct key *key,
 				toksize += RND(token->kad->ticket_len);
 			break;
 
+#ifdef CONFIG_RXGK
 		case RXRPC_SECURITY_YFS_RXGK:
 			toksize += 6 * 8 + 2 * 4;
 			if (!token->no_leak_key)
 				toksize += RND(token->rxgk->key.len);
 			toksize += RND(token->rxgk->ticket.len);
 			break;
+#endif
 
 		default: /* we have a ticket we can't encode */
 			pr_err("Unsupported key token type (%u)\n",
@@ -856,6 +879,7 @@ static long rxrpc_read(const struct key *key,
 				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
 			break;
 
+#ifdef CONFIG_RXGK
 		case RXRPC_SECURITY_YFS_RXGK:
 			ENCODE64(token->rxgk->begintime);
 			ENCODE64(token->rxgk->endtime);
@@ -869,6 +893,7 @@ static long rxrpc_read(const struct key *key,
 				ENCODE_DATA(token->rxgk->key.len, token->rxgk->key.data);
 			ENCODE_DATA(token->rxgk->ticket.len, token->rxgk->ticket.data);
 			break;
+#endif
 
 		default:
 			pr_err("Unsupported key token type (%u)\n",