Messages in this thread Patch in this message | | | From | Nadav Amit <> | Subject | [PATCH] userfaultfd: fix a race between writeprotect and exit_mmap() | Date | Tue, 21 Sep 2021 13:02:47 -0700 |
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From: Nadav Amit <namit@vmware.com>
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@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: stable@vger.kernel.org Fixes: 63b2d4174c4ad ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl") Signed-off-by: Nadav Amit <namit@vmware.com> --- fs/userfaultfd.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 003f0d31743e..22bf14ab2d16 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -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; -- 2.25.1
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