netdev - [PATCH net-next 20/23] rxrpc: Don't leak the service-side session key to userspace

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Message-ID: <160156434215.1728886.7071961658509702368.stgit@warthog.procyon.org.uk>
Date:   Thu, 01 Oct 2020 15:59:02 +0100
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next 20/23] rxrpc: Don't leak the service-side session key
 to userspace

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@...hat.com>
---

 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 8e4ced9b4ecf..333c0f49a9cd 100644
--- a/include/keys/rxrpc-type.h
+++ b/include/keys/rxrpc-type.h
@@ -36,6 +36,7 @@ struct rxkad_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 822152ce381f..c08827b87979 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -579,7 +579,8 @@ 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;
 
 		default: /* we have a ticket we can't encode */
@@ -654,7 +655,10 @@ 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;
 
 		default: