linux-kernel - [PATCH 3.16 225/245] vhost: Check docket sk

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Message-ID: <lsq.1587683028.378990711@decadent.org.uk>
Date:   Fri, 24 Apr 2020 00:07:32 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        "Eugenio Pérez" <eperezma@...hat.com>,
        syzbot+f2a62d07a5198c819c7b@...kaller.appspotmail.com,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 225/245] vhost: Check docket sk_family instead of
 call getname

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eugenio Pérez <eperezma@...hat.com>

commit 42d84c8490f9f0931786f1623191fcab397c3d64 upstream.

Doing so, we save one call to get data we already have in the struct.

Also, since there is no guarantee that getname use sockaddr_ll
parameter beyond its size, we add a little bit of security here.
It should do not do beyond MAX_ADDR_LEN, but syzbot found that
ax25_getname writes more (72 bytes, the size of full_sockaddr_ax25,
versus 20 + 32 bytes of sockaddr_ll + MAX_ADDR_LEN in syzbot repro).

Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server")
Reported-by: syzbot+f2a62d07a5198c819c7b@...kaller.appspotmail.com
Signed-off-by: Eugenio Pérez <eperezma@...hat.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: Also delete "uaddr_len" variable]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -843,11 +843,7 @@ static int vhost_net_release(struct inod
 
 static struct socket *get_raw_socket(int fd)
 {
-	struct {
-		struct sockaddr_ll sa;
-		char  buf[MAX_ADDR_LEN];
-	} uaddr;
-	int uaddr_len = sizeof uaddr, r;
+	int r;
 	struct socket *sock = sockfd_lookup(fd, &r);
 
 	if (!sock)
@@ -859,12 +855,7 @@ static struct socket *get_raw_socket(int
 		goto err;
 	}
 
-	r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa,
-			       &uaddr_len, 0);
-	if (r)
-		goto err;
-
-	if (uaddr.sa.sll_family != AF_PACKET) {
+	if (sock->sk->sk_family != AF_PACKET) {
 		r = -EPFNOSUPPORT;
 		goto err;
 	}