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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@vmware.com
Fixes: 63b2d4174c ("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>
This commit is contained in:
Nadav Amit 2021-10-18 15:15:25 -07:00 committed by Linus Torvalds
parent 8913970c19
commit cb185d5f1e
1 changed files with 9 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
fs/userfaultfd.c
View File

@ -1827,9 +1827,15 @@ 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;