[PATCH 1/5] mountd: reject unknown client IP when !use_ipaddr.

From: NeilBrown <neilb@suse.de>
To: Steve Dickson <SteveD@RedHat.com>
Cc: Linux NFS Mailing list <linux-nfs@vger.kernel.org>
Subject: [PATCH 1/5] mountd: reject unknown client IP when !use_ipaddr.
Date: Thu, 25 Feb 2021 13:42:47 +1100	[thread overview]
Message-ID: <161422096786.28256.16255172827545591674.stgit@noble> (raw)
In-Reply-To: <161422077024.28256.15543036625096419495.stgit@noble>

From: NeilBrown <neil@brown.name>

When use_ipaddr is not in effect, an auth_unix_ip lookup request from
the kernel for an unknown client will be rejected.
When it IS in effect, these requests are always granted with the IP
address being mapped to a string form of the address, preceded by a '$'.

This is inconsistent behaviour and could present a small information
leak.
It means that, for example, a SETCLIENT NFSv4 request may or may not
succeed depending on an internal setting in rpc.mountd.

This is easily rectified by always checking if the client is known.

Signed-off-by: NeilBrown <neil@brown.name>
---
 support/export/cache.c |   17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/support/export/cache.c b/support/export/cache.c
index f1569afb558c..156ebfd4087c 100644
--- a/support/export/cache.c
+++ b/support/export/cache.c
@@ -114,6 +114,7 @@ static void auth_unix_ip(int f)
 	char class[20];
 	char ipaddr[INET6_ADDRSTRLEN + 1];
 	char *client = NULL;
+	struct addrinfo *ai = NULL;
 	struct addrinfo *tmp = NULL;
 	char buf[RPC_CHAN_BUF_SIZE], *bp;
 	int blen;
@@ -139,21 +140,17 @@ static void auth_unix_ip(int f)
 
 	auth_reload();
 
-	/* addr is a valid, interesting address, find the domain name... */
-	if (!use_ipaddr) {
-		struct addrinfo *ai = NULL;
-
-		ai = client_resolve(tmp->ai_addr);
-		if (ai) {
-			client = client_compose(ai);
-			nfs_freeaddrinfo(ai);
-		}
+	/* addr is a valid address, find the domain name... */
+	ai = client_resolve(tmp->ai_addr);
+	if (ai) {
+		client = client_compose(ai);
+		nfs_freeaddrinfo(ai);
 	}
 	bp = buf; blen = sizeof(buf);
 	qword_add(&bp, &blen, "nfsd");
 	qword_add(&bp, &blen, ipaddr);
 	qword_adduint(&bp, &blen, time(0) + DEFAULT_TTL);
-	if (use_ipaddr) {
+	if (use_ipaddr && client) {
 		memmove(ipaddr + 1, ipaddr, strlen(ipaddr) + 1);
 		ipaddr[0] = '$';
 		qword_add(&bp, &blen, ipaddr);


