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

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/[email protected]
Fixes: 0cbb4b4f4c44 ("userfaultfd: clear the vma->vm_userfaultfd_ctx if UFFD_EVENT_FORK fails")
Signed-off-by: Mike Rapoport <[email protected]>
Reported-by: [email protected]
Cc: Andrea Arcangeli <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 594d192b23317d7e69d068b2f124ca6f77de3e07..bad9cea37f12b6e5c95a4a0e4ed78796011d8be5 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -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);