[patch] RDS: fix an integer overflow check

[patch] RDS: fix an integer overflow check

[Dan Carpenter]

"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 <dan.carpenter@oracle.com>

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

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

[Jeff Liu]

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 <dan.carpenter@oracle.com>
>
> 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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Re: [rds-devel] [patch] RDS: fix an integer overflow check

[Jeff Liu]

On 10/13/2012 09:25 PM, Jeff Liu wrote:
> 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 <dan.carpenter@oracle.com>
>>
>> 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)
Sorry, here is a typo.  "start + len" is already well-checked.
Actually, I means there is no other "len + (PAGE_SIZE - 1)" operations.

Thanks,
-Jeff
> 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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>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
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