lkml.org 
[lkml]   [2012]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?)
On 03/02/2012 04:57 PM, Linus Torvalds wrote:
> On Fri, Mar 2, 2012 at 4:38 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> My biggest concern is what happens when this happens to be at the end of
>> mapped kernel memory and we overrun the page?
>
> Yes. It's very unlikely, and it never happens with the dentry data
> itself (the name is always aligned for those).
>
> But it *can* happen if:
>
> - the page contains the filename we copied from user space
>
> - the page is the last page mapped
>
> - the filename is PATH_MAX in size (or very close)
>
> - the last component is sufficiently unaligned
>
> but I was thinking we'd just make sure not to free the last page, and
> just solve it that way.
>
> I was playing around with other ideas (take the page fault and fix it
> up), but those are all really complicated when the notion of "don't
> use the last page" is so much simpler.
>

Note that does mean we need a guard page after each and every
discontiguous RAM range, not just the last one. Raising that issue
since we have had serious bugs in that area in the past.

-hpa




\
 
 \ /
  Last update: 2012-03-03 02:05    [W:0.056 / U:0.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site