[PATCH 47/64] btrfs: Use memset_after() to clear end of struct

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Use memset_after() so memset() doesn't get confused about writing
beyond the destination member that is intended to be the starting point
of zeroing through the end of the struct.

Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 fs/btrfs/root-tree.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 702dc5441f03..ec9e78f65fca 100644
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -39,10 +39,7 @@ static void btrfs_read_root_item(struct extent_buffer *eb, 
int slot,
                need_reset = 1;
        }
        if (need_reset) {
-               memset(&item->generation_v2, 0,
-                       sizeof(*item) - offsetof(struct btrfs_root_item,
-                                       generation_v2));
-
+               memset_after(item, 0, level);
                generate_random_guid(item->uuid);
        }
 }
-- 
2.30.2