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

Jackie Liu
2026-04-01T00:59:22Z

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
>