lkml.org 
[lkml]   [2022]   [Dec]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH-block v3 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg
From

On 12/14/22 11:54, Jens Axboe wrote:
> On 12/13/22 12:53 PM, Waiman Long wrote:
>> On 12/13/22 14:29, Tejun Heo wrote:
>>> On Tue, Dec 13, 2022 at 01:44:45PM -0500, Waiman Long wrote:
>>>> Commit 59b57717fff8 ("blkcg: delay blkg destruction until after
>>>> writeback has finished") delayed call to blkcg_destroy_blkgs() to
>>>> cgwb_release_workfn(). However, it is done after a css_put() of blkcg
>>>> which may be the final put that causes the blkcg to be freed as RCU
>>>> read lock isn't held.
>>>>
>>>> Another place where blkcg_destroy_blkgs() can be called indirectly via
>>>> blkcg_unpin_online() is from the offline_css() function called from
>>>> css_killed_work_fn(). Over there, the potentially final css_put() call
>>>> is issued after offline_css().
>>>>
>>>> By adding a css_tryget() into blkcg_destroy_blkgs() and warning its
>>>> failure, the following stack trace was produced in a test system on
>>>> bootup.
>>> This doesn't agree with the code anymore. Otherwise
>>>
>>> Acked-by: Tejun Heo <tj@kernel.org>
>> Sorry, I overlooked the commit log in my update. I will update it if I need another version, or Jens can make the following edit:
>>
>> css_tryget() -> percpu_ref_is_zero().
> Since the other one also needs an edit, would be great if you could
> just send out a v4.
>
Sure, will do that.

Cheers,
Longman

\
 
 \ /
  Last update: 2022-12-14 17:58    [W:0.273 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site