Re: [V9fs-developer] [PATCH] p9_check_errors() validate PDU length

[jiangyiwen <jiangyiwen@huawei.com>]

On 2018/7/10 6:43, Tomas Bortoli wrote:
> p9_check_errors() does not validate the size of the PDU read
> in p9_parse_header(). Any size can be passed, provoking out-of-bound reads.
> 
> Signed-off-by: Tomas Bortoli <tomasbortoli@gmail.com>
> Reported-by: syzbot+65c6b72f284a39d416b4@syzkaller.appspotmail.com
> ---
> As suggested by Dominique:
> https://lkml.org/lkml/2018/7/9/688
> Such check is not enough as it will prevent to read more than how it has
> been allocated but it won't prevent to read more than how it has been read
> So this patch will require some more changes to prevent bad sizes.
> 
>  net/9p/client.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index 40f7c47f2f74..5b161b576b8a 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -520,10 +520,13 @@ EXPORT_SYMBOL(p9_parse_header);
>  static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
>  {
>  	int8_t type;
> +	int32_t size;
>  	int err;
>  	int ecode;
>  
> -	err = p9_parse_header(req->rc, NULL, &type, NULL, 0);
> +	err = p9_parse_header(req->rc, &size, &type, NULL, 0);
> +	if (size > req->rc->capacity)
> +		return -EINVAL;

Yes, currently 9p client is lacking of properly check for data from server.
Maybe we should have a bigger patch to solve this problem.

>  	/*
>  	 * dump the response from server
>  	 * This should be after check errors which poplulate pdu_fcall.
>