[PATCH AUTOSEL 4.9 23/48] rxrpc: Don't leak the service-side session key to userspace

[Sasha Levin]

From: David Howells <dhowells@xxxxxxxxxx>

[ Upstream commit d2ae4e918218f543214fbd906db68a6c580efbbb ]

Don't let someone reading a service-side rxrpc-type key get access to the
session key that was exchanged with the client.  The server application
will, at some point, need to be able to read the information in the ticket,
but this probably shouldn't include the key material.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/keys/rxrpc-type.h | 1 +
 net/rxrpc/key.c           | 8 ++++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/keys/rxrpc-type.h b/include/keys/rxrpc-type.h
index 5de0673f333b7..865629c5484f5 100644
--- a/include/keys/rxrpc-type.h
+++ b/include/keys/rxrpc-type.h
@@ -88,6 +88,7 @@ struct rxk5_key {
  */
 struct rxrpc_key_token {
 	u16	security_index;		/* RxRPC header security index */
+	bool	no_leak_key;		/* Don't copy the key to userspace */
 	struct rxrpc_key_token *next;	/* the next token in the list */
 	union {
 		struct rxkad_key *kad;
diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index fa475b02bdceb..beb30cca5a4b9 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -1071,7 +1071,8 @@ static long rxrpc_read(const struct key *key,
 		case RXRPC_SECURITY_RXKAD:
 			toksize += 8 * 4;	/* viceid, kvno, key*2, begin,
 						 * end, primary, tktlen */
-			toksize += RND(token->kad->ticket_len);
+			if (!token->no_leak_key)
+				toksize += RND(token->kad->ticket_len);
 			break;
 
 		case RXRPC_SECURITY_RXK5:
@@ -1180,7 +1181,10 @@ static long rxrpc_read(const struct key *key,
 			ENCODE(token->kad->start);
 			ENCODE(token->kad->expiry);
 			ENCODE(token->kad->primary_flag);
-			ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
+			if (token->no_leak_key)
+				ENCODE(0);
+			else
+				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
 			break;
 
 		case RXRPC_SECURITY_RXK5:
-- 
2.27.0