Re: [PATCH] vhost: validate range size before adding to iotlb

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Feb 22, 2022 at 01:23:03AM +0530, Anirudh Rayabharam wrote:
> In vhost_iotlb_add_range_ctx(), validate the range size is non-zero
> before proceeding with adding it to the iotlb.
> 
> Range size can overflow to 0 when start is 0 and last is (2^64 - 1).
> One instance where it can happen is when userspace sends an IOTLB
> message with iova=size=uaddr=0 (vhost_process_iotlb_msg). So, an
> entry with size = 0, start = 0, last = (2^64 - 1) ends up in the
> iotlb. Next time a packet is sent, iotlb_access_ok() loops
> indefinitely due to that erroneous entry:
> 
> 	Call Trace:
> 	 <TASK>
> 	 iotlb_access_ok+0x21b/0x3e0 drivers/vhost/vhost.c:1340
> 	 vq_meta_prefetch+0xbc/0x280 drivers/vhost/vhost.c:1366
> 	 vhost_transport_do_send_pkt+0xe0/0xfd0 drivers/vhost/vsock.c:104
> 	 vhost_worker+0x23d/0x3d0 drivers/vhost/vhost.c:372
> 	 kthread+0x2e9/0x3a0 kernel/kthread.c:377
> 	 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> 	 </TASK>
> 
> Reported by syzbot at:
> 	https://syzkaller.appspot.com/bug?extid=0abd373e2e50d704db87
> 
> Reported-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Tested-by: syzbot+0abd373e2e50d704db87@syzkaller.appspotmail.com
> Signed-off-by: Anirudh Rayabharam <mail@anirudhrb.com>
> ---
>  drivers/vhost/iotlb.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vhost/iotlb.c b/drivers/vhost/iotlb.c
> index 670d56c879e5..b9de74bd2f9c 100644
> --- a/drivers/vhost/iotlb.c
> +++ b/drivers/vhost/iotlb.c
> @@ -53,8 +53,10 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
>  			      void *opaque)
>  {
>  	struct vhost_iotlb_map *map;
> +	u64 size = last - start + 1;
>  
> -	if (last < start)
> +	// size can overflow to 0 when start is 0 and last is (2^64 - 1).

Pls use the old-style /* */  comments.

> +	if (last < start || size == 0)
>  		return -EFAULT;
>  
>  	if (iotlb->limit &&
> @@ -69,7 +71,7 @@ int vhost_iotlb_add_range_ctx(struct vhost_iotlb *iotlb,
>  		return -ENOMEM;
>  
>  	map->start = start;
> -	map->size = last - start + 1;
> +	map->size = size;
>  	map->last = last;
>  	map->addr = addr;
>  	map->perm = perm;
> -- 
> 2.35.1