On Mon, Oct 24, 2022 at 02:32:42PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@xxxxxxxxxx>
>
> Starting in 6.1, CONFIG_FORTIFY_SOURCE checks the length parameter of
> memcpy. Unfortunately, it doesn't handle flex arrays correctly:
>
> ------------[ cut here ]------------
> memcpy: detected field-spanning write (size 48) of single field "dst_bui_fmt" at fs/xfs/xfs_bmap_item.c:628 (size 16)
>
> Fix this by refactoring the xfs_bui_copy_format function to handle the
> copying of the head and the flex array members separately. While we're
> at it, fix a minor validation deficiency in the recovery function.
>
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> ---
> fs/xfs/xfs_bmap_item.c | 46 ++++++++++++++++++++++------------------------
> fs/xfs/xfs_ondisk.h | 5 +++++
> 2 files changed, 27 insertions(+), 24 deletions(-)
>
>
> diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> index 51f66e982484..a1da6205252b 100644
> --- a/fs/xfs/xfs_bmap_item.c
> +++ b/fs/xfs/xfs_bmap_item.c
> @@ -608,28 +608,18 @@ static const struct xfs_item_ops xfs_bui_item_ops = {
> .iop_relog = xfs_bui_item_relog,
> };
>
> -/*
> - * Copy an BUI format buffer from the given buf, and into the destination
> - * BUI format structure. The BUI/BUD items were designed not to need any
> - * special alignment handling.
> - */
> -static int
> +static inline void
> xfs_bui_copy_format(
> - struct xfs_log_iovec *buf,
> - struct xfs_bui_log_format *dst_bui_fmt)
> + struct xfs_bui_log_format *dst,
> + const struct xfs_bui_log_format *src)
> {
> - struct xfs_bui_log_format *src_bui_fmt;
> - uint len;
> + unsigned int i;
>
> - src_bui_fmt = buf->i_addr;
> - len = xfs_bui_log_format_sizeof(src_bui_fmt->bui_nextents);
> + memcpy(dst, src, offsetof(struct xfs_bui_log_format, bui_extents));
I think this would work:
*dst = *src;
>
> - if (buf->i_len == len) {
> - memcpy(dst_bui_fmt, src_bui_fmt, len);
> - return 0;
> - }
> - XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, NULL);
> - return -EFSCORRUPTED;
> + for (i = 0; i < src->bui_nextents; i++)
> + memcpy(&dst->bui_extents[i], &src->bui_extents[i],
> + sizeof(struct xfs_map_extent));
Same here:
dst->bui_extents[i] = src->bui_extents[i];
No reason to bring memcpy into this at all. :)
--
Kees Cook
