Re: [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap()

[Peter Xu]

On Tue, Sep 21, 2021 at 01:02:47PM -0700, Nadav Amit wrote:
> From: Nadav Amit <namit@xxxxxxxxxx>
> 
> A race is possible when a process exits, its VMAs are removed
> by exit_mmap() and at the same time userfaultfd_writeprotect() is
> called.
> 
> The race was detected by KASAN on a development kernel, but it appears
> to be possible on vanilla kernels as well.
> 
> Use mmget_not_zero() to prevent the race as done in other userfaultfd
> operations.
> 
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>

Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>

Thanks!

-- 
Peter Xu