[cip-dev] [PATCH 4.4] vhost: Check docket sk_family instead of call getname

[cip-dev] [PATCH 4.4] vhost: Check docket sk_family instead of call getname

[Pavel Machek]

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From: Eugenio Pérez <eperezma@redhat.com>

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>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Upstream: 42d84c8490f9f0931786f1623191fcab397c3d64
Signed-off-by: Pavel Machek <pavel@denx.de>
---
 drivers/vhost/net.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

---

Since it is a security problem, I backported the patch to 4.4. I
compile tested it on cip test farm, but it was only built for single
target, probably due to too big config.

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 1459dc9fd701..5efac33c29dc 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -815,11 +815,7 @@ 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 uaddr_len = sizeof uaddr, r;
+	int r;
 	struct socket *sock = sockfd_lookup(fd, &r);
 
 	if (!sock)
@@ -831,12 +827,7 @@ static struct socket *get_raw_socket(int fd)
 		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;
 	}
-- 
2.20.1


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: [cip-dev] [PATCH 4.4] vhost: Check docket sk_family instead of call getname

[Punit Agrawal]

Hi Pavel,

A couple of comments below -

Pavel Machek <pavel@ucw.cz> writes:

> From: Eugenio Pérez <eperezma@redhat.com>
>
> 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>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Upstream: 42d84c8490f9f0931786f1623191fcab397c3d64

Please follow the style guidelines documented in
Documentation/process/stable-kernel-rules.rst. In this instance, please
mention the upstream commit id following -

    The upstream commit ID must be specified with a separate line above the
    commit
    text, like this:

        commit <sha1> upstream.

For an example, take a look at Commit ad598a48fe61 ("vhost: Check docket
sk_family instead of call getname"). It's a backport of the same
upstream patch to 4.19 stable kernel.

> Signed-off-by: Pavel Machek <pavel@denx.de>
> ---
>  drivers/vhost/net.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
>
> ---
>
> Since it is a security problem, I backported the patch to 4.4. I
> compile tested it on cip test farm, but it was only built for single
> target, probably due to too big config.
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 1459dc9fd701..5efac33c29dc 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -815,11 +815,7 @@ 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 uaddr_len = sizeof uaddr, r;
> +	int r;
>  	struct socket *sock = sockfd_lookup(fd, &r);
>  
>  	if (!sock)
> @@ -831,12 +827,7 @@ static struct socket *get_raw_socket(int fd)
>  		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;
>  	}
> -- 
> 2.20.1

This patch fails to apply with the following error -

    % git am vhost.mbox
    Applying: vhost: Check docket sk_family instead of call getname
    error: corrupt patch at line 16
    Patch failed at 0001 vhost: Check docket sk_family instead of call
    getname
    hint: Use 'git am --show-current-patch' to see the failed patch
    When you have resolved this problem, run "git am --continue".
    If you prefer to skip this patch, run "git am --skip" instead.
    To restore the original branch and stop patching, run "git am --abort".

There is some encoding issue in your mail client. The same workflow
works for other kernel patches.

Thanks,
Punit
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