Linux Virtualization - May 2018 - [PATCH net] vhost: Use kzalloc() to allocate vhost_msg_node

On Fri, Apr 27, 2018 at 11:45:02AM -0400, Kevin Easton
wrote:
> The struct vhost_msg within struct vhost_msg_node is copied to userspace,
> so it should be allocated with kzalloc() to ensure all structure padding
> is zeroed.
> 
> Signed-off-by: Kevin Easton <kevin at guarana.org>
> Reported-by: syzbot+87cfa083e727a224754b at syzkaller.appspotmail.com
> ---
>  drivers/vhost/vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f3bd8e9..1b84dcff 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2339,7 +2339,7 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
>  /* Create a new message. */
>  struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
>  {
> -	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
> +	struct vhost_msg_node *node = kzalloc(sizeof *node, GFP_KERNEL);
>  	if (!node)
>  		return NULL;
>  	node->vq = vq;

Let's just init the msg though.

OK it seems this is the best we can do for now,
we need a new feature bit to fix it for 32 bit
userspace on 64 bit kernels.

Does the following help?

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index f3bd8e9..58d9aec 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2342,6 +2342,9 @@ struct vhost_msg_node *vhost_new_msg(struct
vhost_virtqueue *vq, int type)
 	struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
 	if (!node)
 		return NULL;
+
+	/* Make sure all padding within the structure is initialized. */
+	memset(&node->msg, 0, sizeof node->msg);
 	node->vq = vq;
 	node->msg.type = type;
 	return node;

On Mon, May 7, 2018 at 3:03 PM, Michael S. Tsirkin <mst at redhat.com>
wrote:
> On Fri, Apr 27, 2018 at 11:45:02AM -0400, Kevin Easton wrote:
>> The struct vhost_msg within struct vhost_msg_node is copied to
userspace,
>> so it should be allocated with kzalloc() to ensure all structure
padding
>> is zeroed.
>>
>> Signed-off-by: Kevin Easton <kevin at guarana.org>
>> Reported-by: syzbot+87cfa083e727a224754b at syzkaller.appspotmail.com
>> ---
>>  drivers/vhost/vhost.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index f3bd8e9..1b84dcff 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -2339,7 +2339,7 @@ EXPORT_SYMBOL_GPL(vhost_disable_notify);
>>  /* Create a new message. */
>>  struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int
type)
>>  {
>> -     struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
>> +     struct vhost_msg_node *node = kzalloc(sizeof *node, GFP_KERNEL);
>>       if (!node)
>>               return NULL;
>>       node->vq = vq;
>
>
> Let's just init the msg though.
>
> OK it seems this is the best we can do for now,
> we need a new feature bit to fix it for 32 bit
> userspace on 64 bit kernels.
>
> Does the following help?
Hi Michael,

You can ask reporter (syzbot) to test:
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#testing-patches
https://github.com/google/syzkaller/blob/master/docs/syzbot.md#kmsan-bugs

> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index f3bd8e9..58d9aec 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2342,6 +2342,9 @@ struct vhost_msg_node *vhost_new_msg(struct
vhost_virtqueue *vq, int type)
>         struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
>         if (!node)
>                 return NULL;
> +
> +       /* Make sure all padding within the structure is initialized. */
> +       memset(&node->msg, 0, sizeof node->msg);
>         node->vq = vq;
>         node->msg.type = type;
>         return node;
>
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