[PATCH] vhost: Check docket sk_family instead of call getname

[PATCH] vhost: Check docket sk_family instead of call getname

[Eugenio Pérez]

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@syzkaller.appspotmail.com
Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 drivers/vhost/net.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index e158159671fa..18e205eeb9af 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -1414,10 +1414,6 @@ static int vhost_net_release(struct inode *inode, struct file *f)
 
 static struct socket *get_raw_socket(int fd)
 {
-	struct {
-		struct sockaddr_ll sa;
-		char  buf[MAX_ADDR_LEN];
-	} uaddr;
 	int r;
 	struct socket *sock = sockfd_lookup(fd, &r);
 
@@ -1430,11 +1426,7 @@ static struct socket *get_raw_socket(int fd)
 		goto err;
 	}
 
-	r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa, 0);
-	if (r < 0)
-		goto err;
-
-	if (uaddr.sa.sll_family != AF_PACKET) {
+	if (sock->sk->sk_family != AF_PACKET) {
 		r = -EPFNOSUPPORT;
 		goto err;
 	}
-- 
2.18.1

Re: [PATCH] vhost: Check docket sk_family instead of call getname

[Michael S. Tsirkin]

On Fri, Feb 21, 2020 at 12:06:56PM +0100, Eugenio Pérez wrote:
> 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@syzkaller.appspotmail.com
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>


Thanks for debugging this!

Acked-by: Michael S. Tsirkin <mst@redhat.com>





> ---
>  drivers/vhost/net.c | 10 +---------
>  1 file changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index e158159671fa..18e205eeb9af 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1414,10 +1414,6 @@ static int vhost_net_release(struct inode *inode, struct file *f)
>  
>  static struct socket *get_raw_socket(int fd)
>  {
> -	struct {
> -		struct sockaddr_ll sa;
> -		char  buf[MAX_ADDR_LEN];
> -	} uaddr;
>  	int r;
>  	struct socket *sock = sockfd_lookup(fd, &r);
>  
> @@ -1430,11 +1426,7 @@ static struct socket *get_raw_socket(int fd)
>  		goto err;
>  	}
>  
> -	r = sock->ops->getname(sock, (struct sockaddr *)&uaddr.sa, 0);
> -	if (r < 0)
> -		goto err;
> -
> -	if (uaddr.sa.sll_family != AF_PACKET) {
> +	if (sock->sk->sk_family != AF_PACKET) {
>  		r = -EPFNOSUPPORT;
>  		goto err;
>  	}
> -- 
> 2.18.1

Re: [PATCH] vhost: Check docket sk_family instead of call getname

[David Miller]

From: Eugenio Pérez <eperezma@redhat.com>
Date: Fri, 21 Feb 2020 12:06:56 +0100

> 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@syzkaller.appspotmail.com
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>

Applied and queued up for -stable, thanks.