Re: [PATCH] drivers/xen/grant-table.c: Be sure of unsigned value never comparing with 0
From: David Vrabel
Date: Wed Aug 27 2014 - 06:06:36 EST
On 26/08/14 20:42, Chen Gang wrote:
> On 08/27/2014 01:03 AM, David Vrabel wrote:
>> On 26/08/14 16:38, Chen Gang wrote:
>>> In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may
>>> be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than
>>> 'nr_glist_frames' in failure processing, which cause infinite looping.
>> nr_grant_frames is at least 1. See gnttab_init().
> OK, thanks, that sounds reasonable to me, it is not a real wold bug, it
> is my fault. :-)
>>> --- a/drivers/xen/grant-table.c
>>> +++ b/drivers/xen/grant-table.c
>>> @@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
>>> return 0;
>>> - for ( ; i >= nr_glist_frames; i--)
>>> - free_page((unsigned long) gnttab_list[i]);
>>> + while (i > nr_glist_frames)
>>> + free_page((unsigned long) gnttab_list[--i]);
>> while (i-- > nr_glist_frames)
>> Would have been better.
> OK, thanks, that sounds reasonable to me.
> If necessary to send patch v2 (change comments and contents), please
> let me know, and I shall send.
Applied to devel/for-linus-3.18 with this description:
xen/grant-table: refactor error cleanup in grow_gnttab_list()
The cleanup loop in grow_gnttab_list() is safe from the underflow of
the unsigned 'i' since nr_glist_frames is >= 1, but refactor it
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