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


Hi Pavel,

A couple of comments below -

Pavel Machek <pavel@...> writes:

From: Eugenio Pérez <eperezma@...>

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@...
Signed-off-by: Eugenio Pérez <eperezma@...>
Acked-by: Michael S. Tsirkin <mst@...>
Signed-off-by: David S. Miller <davem@...>
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
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@...>
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_len, 0);
- if (r)
- goto err;
- if ( != AF_PACKET) {
+ if (sock->sk->sk_family != AF_PACKET) {
goto err;
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
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.


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