userfaultfd: clear flag if remap event not enabled

When the process being tracked does mremap() without
UFFD_FEATURE_EVENT_REMAP on the corresponding tracking uffd file handle,
we should not generate the remap event, and at the same time we should
clear all the uffd flags on the new VMA.  Without this patch, we can still
have the VM_UFFD_MISSING|VM_UFFD_WP flags on the new VMA even the fault
handling process does not even know the existance of the VMA.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Andrea Arcangeli <[email protected]>
Acked-by: Mike Rapoport <[email protected]>
Reviewed-by: William Kucharski <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Pavel Emelyanov <[email protected]>
Cc: Pravin Shedge <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index e211b99d33c4..89800fc7dc9d 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -735,10 +735,18 @@ void mremap_userfaultfd_prep(struct vm_area_struct *vma,
 	struct userfaultfd_ctx *ctx;
 
 	ctx = vma->vm_userfaultfd_ctx.ctx;
-	if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
+
+	if (!ctx)
+		return;
+
+	if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
 		vm_ctx->ctx = ctx;
 		userfaultfd_ctx_get(ctx);
 		WRITE_ONCE(ctx->mmap_changing, true);
+	} else {
+		/* Drop uffd context if remap feature not enabled */
+		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
+		vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
 	}
 }