userfaultfd: clear flag if remap event not enabled

[ Upstream commit 3cfd22be0ad663248fadfc8f6ffa3e255c394552 ]

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/20181211053409.20317-1-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Cc: Pravin Shedge <pravin.shedge4linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 7a85e609fc276f28dd80c8dc481e383094d1dfe9..d8b8323e80f41d25fce82e0b4b5db24f95471a46 100644 (file)
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -736,10 +736,18 @@ 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);
        }
 }