vhost: Check docket sk_family instead of call getname

From: Eugenio Pérez <[email protected]>

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).

Upstream: 42d84c8490f9f0931786f1623191fcab397c3d64

---
 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.

index 1459dc9fd701..5efac33c29dc 100644
@@ -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


-- 
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Hi Pavel,

A couple of comments below -

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.

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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