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

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Message-Id: <20200821130337.f4d1f5cd665ab149e1f43ed5@linux-foundation.org>
Date:   Fri, 21 Aug 2020 13:03:37 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yang Shi <shy828301@...il.com>
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, 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!