The patch titled
Subject: userfaultfd: fix a race between writeprotect and exit_mmap()
has been added to the -mm tree. Its filename is
userfaultfd-fix-a-race-between-writeprotect-and-exit_mmap.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-fix-a-race-between-writeprotect-and-exit_mmap.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-fix-a-race-between-writeprotect-and-exit_mmap.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Nadav Amit <namit@xxxxxxxxxx>
Subject: userfaultfd: fix a race between writeprotect and exit_mmap()
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.
Link: https://lkml.kernel.org/r/20210921200247.25749-1-namit@xxxxxxxxxx
Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Tested-by: Li Wang <liwang@xxxxxxxxxx>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
--- a/fs/userfaultfd.c~userfaultfd-fix-a-race-between-writeprotect-and-exit_mmap
+++ a/fs/userfaultfd.c
@@ -1827,9 +1827,15 @@ static int userfaultfd_writeprotect(stru
if (mode_wp && mode_dontwake)
return -EINVAL;
- ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
- uffdio_wp.range.len, mode_wp,
- &ctx->mmap_changing);
+ if (mmget_not_zero(ctx->mm)) {
+ ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
+ uffdio_wp.range.len, mode_wp,
+ &ctx->mmap_changing);
+ mmput(ctx->mm);
+ } else {
+ return -ESRCH;
+ }
+
if (ret)
return ret;
_
Patches currently in -mm which might be from namit@xxxxxxxxxx are
userfaultfd-fix-a-race-between-writeprotect-and-exit_mmap.patch
