[PATCH 2/2] xfs: Use flex_cpy() to check extent copying

[Kees Cook]

Use flex_cpy() instead of memcpy() to copy the bui_fmt flexible array
structure, which will perform bounds checking internally. Avoids the
false positive warning seen under FORTIFY_SOURCE:

  memcpy: detected field-spanning write (size 48) of single field "dst_bui_fmt" at fs/xfs/xfs_bmap_item.c:628 (size 16)

Reported-by: Zorro Lang <zlang@xxxxxxxxxx>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216563
Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx>
Cc: linux-xfs@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/xfs/xfs_bmap_item.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
index 51f66e982484..5f135893df66 100644
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -24,6 +24,7 @@
 #include "xfs_error.h"
 #include "xfs_log_priv.h"
 #include "xfs_log_recover.h"
+#include <linux/flex_array.h>
 
 struct kmem_cache	*xfs_bui_cache;
 struct kmem_cache	*xfs_bud_cache;
@@ -624,10 +625,10 @@ xfs_bui_copy_format(
 	src_bui_fmt = buf->i_addr;
 	len = xfs_bui_log_format_sizeof(src_bui_fmt->bui_nextents);
 
-	if (buf->i_len == len) {
-		memcpy(dst_bui_fmt, src_bui_fmt, len);
+	if (buf->i_len == len &&
+	    __flex_cpy(dst_bui_fmt, src_bui_fmt,
+		       bui_extents, bui_nextents, __passthru) == 0)
 		return 0;
-	}
 	XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, NULL);
 	return -EFSCORRUPTED;
 }
-- 
2.34.1