Subject: Re: [PATCH v5 2/2] KEYS: Avoid false positive ENOMEM error on key read

From: Jarkko Sakkinen <[email-masked]>
Date: Fri, 20 Mar 2020 04:07:17 +0200

On Thu, Mar 19, 2020 at 08:07:55PM -0400, Waiman Long wrote:
> On 3/19/20 3:46 PM, Jarkko Sakkinen wrote:
> > On Wed, Mar 18, 2020 at 06:14:57PM -0400, Waiman Long wrote:
> >> +			 * It is possible, though unlikely, that the key
> >> +			 * changes in between the up_read->down_read period.
> >> +			 * If the key becomes longer, we will have to
> >> +			 * allocate a larger buffer and redo the key read
> >> +			 * again.
> >> +			 */
> >> +			if (!tmpbuf || unlikely(ret > tmpbuflen)) {
> > Shouldn't you check that tmpbuflen stays below buflen (why else
> > you had made copy of buflen otherwise)?
> 
> The check above this thunk:
> 
> if ((ret > 0) && (ret <= buflen)) {
> 
> will make sure that ret will not be larger than buflen. So tmpbuflen
> will never be bigger than buflen.

Ah right, of course, thanks.

What would go wrong if the condition was instead
((ret > 0) && (ret <= tmpbuflen))?

/Jarkko