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

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Message-Id: <20210727205855.411487-48-keescook@chromium.org>
Date:   Tue, 27 Jul 2021 13:58:38 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Keith Packard <keithpac@...zon.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-staging@...ts.linux.dev, linux-block@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH 47/64] btrfs: Use memset_after() to clear end of struct

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 <keescook@...omium.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