Re: [PATCH] mm/mempolicy: fix memory leak in weighted_interleave_auto_store()

["Jackie Liu" <liu.yun@linux.dev>]

2026年4月1日 03:21, "Joshua Hahn" <joshua.hahnjy@gmail.com mailto:joshua.hahnjy@gmail.com?to=%22Joshua%20Hahn%22%20%3Cjoshua.hahnjy%40gmail.com%3E > 写到:


> 
> On Tue, 31 Mar 2026 12:01:10 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > 
> > On Tue, 31 Mar 2026 12:53:40 -0400 Gregory Price <gourry@gourry.net> wrote:
> >  
> >  On Tue, Mar 31, 2026 at 06:07:40PM +0800, Jackie Liu wrote:
> >  > From: Jackie Liu <liuyun01@kylinos.cn>
> >  > 
> >  > Add the missing kfree(new_wi_state) when the auto mode is already set
> >  > to the requested value. When a user writes "false" to the auto sysfs
> >  > interface and the current mode is already manual (mode_auto == false),
> >  > the function returns early without freeing new_wi_state allocated at
> >  > the beginning of the function. This can be triggered repeatedly from
> >  > userspace, leaking memory on each write.
> >  > 
> >  > Fixes: e341f9c3c841 ("mm/mempolicy: Weighted Interleave Auto-tuning")
> >  > Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
> >  
> >  ..
> > 
> >  > --- a/mm/mempolicy.c
> >  > +++ b/mm/mempolicy.c
> >  > @@ -3713,6 +3713,7 @@ static ssize_t weighted_interleave_auto_store(struct kobject *kobj,
> >  > goto update_wi_state;
> >  > if (input == old_wi_state->mode_auto) {
> >  > mutex_unlock(&wi_state_lock);
> >  > + kfree(new_wi_state);
> >  > return count;
> >  > }
> >  > 
> >  
> >  Thanks all.
> >  
> >  Am I correct in believing that triggering this leak requires elevated
> >  privileges?
> > 
> Hello Andrew, I hope you are doing well : -)
> 
> Yes indeed, writing to the file requires elevated privileges.
> 
> While going to check this out, however, I noticed a different bug which is
> that the file is no longer called "auto", but called "__auto_type".
> I suspected this was the result of a newly defined macro, and surely...
> commit 6cce897a37dc "compiler_types.h: add "auto" as a macro for "__auto_type""
> seems to have defined auto to always expand out to __auto_type.
> 
> Of course for using the __ATTR(name, permissions, show, store) macro this
> is bad because writing "auto" there no longer works...
> 
> I'll send up a quick fix to just manually write out the name instead.
> Doing a quick grep for the pattern thankfully seems to only point to this.
> I do think it is a bit weird to pass a raw, unquoted string into the macro...
> 
> > 
> > I'll add cc:stable to this and shall queue it for 7.1-rc1. 
> >  This means (I assume) that its entry into the -stable trees might be a
> >  little later than if we were to upstream it immediately.
> >  
> >  AI review liked this patch but claims to have found another one:
> >  https://sashiko.dev/#/patchset/20260331100740.84906-1-liu.yun@linux.dev
> > 
> Sashiko seems to be correct here. Pretty neat that it was able to catch
> a related bug when analyzing the correctness of this fix!

Thank you. I quickly wrote a patch and sent it. Sashiko looks amazing.

The link is https://lore.kernel.org/all/20260401005702.7096-1-liu.yun@linux.dev/

Please help me review it again.

-- 
Jackie Liu

> 
> I can send up a fix for this one too, or leave it to you Jackie, whichever
> you prefer! Just let me know : -) I'll go ahead and send a fix for the
> naming issue though, since that one seems orthogonal to this.
> 
> Thank you, and I hope you have a great day!
> Joshua
>