Re: KASAN: use-after-free Read in do_madvise

[Andrew Morton]

On Fri, 21 Aug 2020 10:15:45 -0700 Yang Shi <shy828301@xxxxxxxxx> 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!