Subject: Re: [patch] RDS: fix an integer overflow check

From: Jeff Liu <[email-masked]>
Date: Sat, 13 Oct 2012 21:25:40 +0800

On 10/12/2012 03:31 PM, Dan Carpenter wrote:
> "len" is an int.  We verified that len was postive already.  Since
> PAGE_SIZE is specified as an unsigned long, the type it promoted to
> unsigned and the condition is never true.
>
> I'm not sure this check is actually needed.  It might be that we could
> just remove it?
>
> Signed-off-by: Dan Carpenter <[email-masked]>
>
> diff --git a/net/rds/info.c b/net/rds/info.c
> index 9a6b4f6..4d62618 100644
> --- a/net/rds/info.c
> +++ b/net/rds/info.c
> @@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
>   
>   	/* check for all kinds of wrapping and the like */
>   	start = (unsigned long)optval;
> -	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
Looks the original thought is to check up len + (PAGE_SIZE - 1) < len to 
avoid integer overflow, but lack of a "()".

However, we only have one add operation in this function which were 
shown as following:
         nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
                         >> PAGE_SHIFT;

I also gone through the call chains, there is no other (start + len) 
operations for all transport, I think it's safe to remove this check up 
if so.

Thanks,
-Jeff
> +	if (len < 0 || len > INT_MAX - (PAGE_SIZE - 1) || start + len < start) {
>   		ret = -EINVAL;
>   		goto out;
>   	}
> --
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