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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Wed, 18 May 2022 10:52:51 +0200
Message-ID: <CACT4Y+ZkDJmoaT5ks8cmhzaNhhgaLYAhvzx+5q3yzKQEW1LZ5A@mail.gmail.com>
Subject: Re: [PATCH] mm/mempolicy: fix uninit-value in mpol_rebind_policy()
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Wang Cheng <wanngchenng@gmail.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        syzbot+ad1b8c404f0959c4bfcc@syzkaller.appspotmail.com
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On Wed, 18 May 2022 at 02:08, Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 16 May 2022 17:47:26 +0800 Wang Cheng <wanngchenng@gmail.com> wrote:
>
> >
> > ...
> >
> > This patch seems to fix below bug too.
> > KMSAN: uninit-value in mpol_rebind_mm (2)
> > https://syzkaller.appspot.com/bug?id=f2fecd0d7013f54ec4162f60743a2b28df40926b
> >
> > The uninit-value is pol->w.cpuset_mems_allowed in mpol_rebind_policy().
> > When syzkaller reproducer runs to the beginning of mpol_new(),
> >
> >           mpol_new() mm/mempolicy.c
> >         do_mbind() mm/mempolicy.c
> >       kernel_mbind() mm/mempolicy.c
> >
> > `mode` is 1(MPOL_PREFERRED), nodes_empty(*nodes) is `true` and `flags`
> > is 0. Then
> >
> >       mode = MPOL_LOCAL;
> >       ...
> >       policy->mode = mode;
> >       policy->flags = flags;
> >
> > will be executed. So in mpol_set_nodemask(),
> >
> >           mpol_set_nodemask() mm/mempolicy.c
> >         do_mbind()
> >       kernel_mbind()
> >
> > pol->mode is 4(MPOL_LOCAL), that `nodemask` in `pol` is not initialized,
> > which will be accessed in mpol_rebind_policy().
>
> Thanks, I added the above to the changelog and I plan to import the
> result into mm-stable later this week.
>
> > IIUC, "#syz fix: mm/mempolicy: fix uninit-value in mpol_rebind_policy()"
> > could be sent to syzbot+ad1b8c404f0959c4bfcc@syzkaller.appspotmail.com
> > to attach the fixing commit to the bug. WDYT?
>
> Could be.  The "syz fix" isn't a thing I've paid much attention to.
> I'll start doing so ;)

Yes, we can send:

#syz fix: mm/mempolicy: fix uninit-value in mpol_rebind_policy()

to syzbot+ad1b8c404f0959c4bfcc@syzkaller.appspotmail.com
and now it should be reflected at:
https://syzkaller.appspot.com/bug?extid=ad1b8c404f0959c4bfcc

and the bug will be closed when the fix is merged everywhere.