From 149958ecd0627a9f1e9c678c25c665400054cd6a Mon Sep 17 00:00:00 2001
From: Nadav Amit <namit@vmware.com>
Date: Mon, 18 Oct 2021 15:15:25 -0700
Subject: [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap()
Git-commit: cb185d5f1ebf900f4ae3bf84cee212e6dd035aca
Patch-mainline: v5.15-rc7
References: stable-5.14.15
commit cb185d5f1ebf900f4ae3bf84cee212e6dd035aca upstream.
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@vmware.com
Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
Signed-off-by: Nadav Amit <namit@vmware.com>
Tested-by: Li Wang <liwang@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
fs/userfaultfd.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index c830cc4ea60f..a87af3333739 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1826,9 +1826,15 @@ static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
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;
--
2.26.2