Commit 31e810aa authored Aug 02, 2018 by Mike Rapoport Committed by Linus Torvalds Aug 02, 2018

userfaultfd: remove uffd flags from vma->vm_flags if UFFD_EVENT_FORK fails

The fix in commit 0cbb4b4f ("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: 0cbb4b4f ("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>

parent eec3636a

fs/userfaultfd.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -633,8 +633,10 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
		/* the various vma->vm_userfaultfd_ctx still points to it */
		down_write(&mm->mmap_sem);
		for (vma = mm->mmap; vma; vma = vma->vm_next)
		if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx)
		if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
		vma->vm_flags &= ~(VM_UFFD_WP \| VM_UFFD_MISSING);
		}
		up_write(&mm->mmap_sem);

		userfaultfd_ctx_put(release_new_ctx);

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