userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails
authorMike Rapoport <rppt@linux.vnet.ibm.com>
Thu, 2 Aug 2018 22:36:09 +0000 (15:36 -0700)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Mon, 6 Aug 2018 14:20:49 +0000 (16:20 +0200)
commit0eba9f5d3d4829fe5cc53abe90a73c33f47405af
treebdd6c6901d49d20ec7ba5cde02e89ece13358fb3
parenta1b5bcffe4a4e6740545fe8ab4a3381da148ce89
userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails

commit 31e810aa1033a7db50a2746cd34a2432237f6420 upstream.

The fix in commit 0cbb4b4f4c44 ("userfaultfd: clear the
vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails") cleared the
vma->vm_userfaultfd_ctx but kept userfaultfd flags in vma->vm_flags
that were copied from the parent process VMA.

As the result, there is an inconsistency between the values of
vma->vm_userfaultfd_ctx.ctx and vma->vm_flags which triggers BUG_ON
in userfaultfd_release().

Clearing the uffd flags from vma->vm_flags in case of UFFD_EVENT_FORK
failure resolves the issue.

Link: http://lkml.kernel.org/r/1532931975-25473-1-git-send-email-rppt@linux.vnet.ibm.com
Fixes: 0cbb4b4f4c44 ("userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails")
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reported-by: syzbot+121be635a7a35ddb7dcb@syzkaller.appspotmail.com
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Eric Biggers <ebiggers3@gmail.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>
fs/userfaultfd.c