linux-kernel - Re: KASAN: use-after-free Read in do

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Date:   Fri, 21 Aug 2020 13:34:17 -0700
From:   Yang Shi <shy828301@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     syzbot <syzbot+b90df26038d1d5d85c97@...kaller.appspotmail.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, syzkaller-bugs@...glegroups.com,
        Jan Kara <jack@...e.cz>
Subject: Re: KASAN: use-after-free Read in do_madvise

On Fri, Aug 21, 2020 at 1:03 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri, 21 Aug 2020 10:15:45 -0700 Yang Shi <shy828301@...il.com> wrote:
>
> > It looks the vma is gone. The below patch should be able to fix it:
> >
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index dd1d43cf026d..d4aa5f776543 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -289,9 +289,9 @@ static long madvise_willneed(struct vm_area_struct *vma,
> >          */
> >         *prev = NULL;   /* tell sys_madvise we drop mmap_lock */
> >         get_file(file);
> > -       mmap_read_unlock(current->mm);
> >         offset = (loff_t)(start - vma->vm_start)
> >                         + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> > +       mmap_read_unlock(current->mm);
> >         vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
> >         fput(file);
> >         mmap_read_lock(current->mm);
>
> Oh geeze.  Can you please send this along as a real patch, cc:stable,
> Fixes: 692fe62433d4c?  Please cc Jan!

Yes, sure. Working on a real patch now.