Re: [PATCH 003/119] xfs: check offsets of variable length structures
From: Brian Foster <hidden>
Date: 2016-06-20 12:40:09
Also in:
linux-fsdevel
On Sat, Jun 18, 2016 at 11:01:33AM -0700, Darrick J. Wong wrote:
On Fri, Jun 17, 2016 at 01:34:27PM -0400, Brian Foster wrote:quoted
On Thu, Jun 16, 2016 at 06:18:12PM -0700, Darrick J. Wong wrote:quoted
Some of the directory/attr structures contain variable-length objects, so the enclosing structure doesn't have a meaningful fixed size at compile time. We can check the offsets of the members before the variable-length member, so do those. Signed-off-by: Darrick J. Wong <redacted> ---I'm missing why this is necessary. Is the intent still to catch alignment and/or padding issues? If so, isn't the size check sufficient, regardless of trailing variable size fields? Perhaps the goal here is to reduce the scope of checking from where it isn't needed..? For example, xfs_dir2_data_unused_t looks like it has a field where the offset in the structure is irrelevant, so that's a possible false positive if that changes down the road. On the flip side, that doesn't appear to be the case for other structures such as xfs_attr_leaf_name_[local|remote]_t.ISTR making this change to work around behavioral variances in how much padding gcc adds to structures across its various targets. The macros that go along with the variable sized structures work fine, but testing the sizeof() doesn't work reliably.
Ok, I take that to mean that we may or may not have padding in some of the variable structures depending on architecture (and we really only care about certain fields in those structures). Fair enough, thanks! Brian
--Dquoted
Brianquoted
fs/xfs/xfs_ondisk.h | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-)diff --git a/fs/xfs/xfs_ondisk.h b/fs/xfs/xfs_ondisk.h index 184c44e..0272301 100644 --- a/fs/xfs/xfs_ondisk.h +++ b/fs/xfs/xfs_ondisk.h@@ -22,6 +22,11 @@ BUILD_BUG_ON_MSG(sizeof(structname) != (size), "XFS: sizeof(" \ #structname ") is wrong, expected " #size) +#define XFS_CHECK_OFFSET(structname, member, off) \ + BUILD_BUG_ON_MSG(offsetof(structname, member) != (off), \ + "XFS: offsetof(" #structname ", " #member ") is wrong, " \ + "expected " #off) + static inline void __init xfs_check_ondisk_structs(void) {@@ -75,15 +80,28 @@ xfs_check_ondisk_structs(void) XFS_CHECK_STRUCT_SIZE(xfs_attr_leaf_name_remote_t, 12); */ + XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, valuelen, 0); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, namelen, 2); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_local_t, nameval, 3); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, valueblk, 0); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, valuelen, 4); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, namelen, 8); + XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, name, 9); XFS_CHECK_STRUCT_SIZE(xfs_attr_leafblock_t, 40); - XFS_CHECK_STRUCT_SIZE(xfs_attr_shortform_t, 8); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, hdr.totsize, 0); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, hdr.count, 2); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].namelen, 4); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].valuelen, 5); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].flags, 6); + XFS_CHECK_OFFSET(xfs_attr_shortform_t, list[0].nameval, 7); XFS_CHECK_STRUCT_SIZE(xfs_da_blkinfo_t, 12); XFS_CHECK_STRUCT_SIZE(xfs_da_intnode_t, 16); XFS_CHECK_STRUCT_SIZE(xfs_da_node_entry_t, 8); XFS_CHECK_STRUCT_SIZE(xfs_da_node_hdr_t, 16); XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_free_t, 4); XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_hdr_t, 16); - XFS_CHECK_STRUCT_SIZE(xfs_dir2_data_unused_t, 6); + XFS_CHECK_OFFSET(xfs_dir2_data_unused_t, freetag, 0); + XFS_CHECK_OFFSET(xfs_dir2_data_unused_t, length, 2); XFS_CHECK_STRUCT_SIZE(xfs_dir2_free_hdr_t, 16); XFS_CHECK_STRUCT_SIZE(xfs_dir2_free_t, 16); XFS_CHECK_STRUCT_SIZE(xfs_dir2_ino4_t, 4);@@ -94,6 +112,9 @@ xfs_check_ondisk_structs(void) XFS_CHECK_STRUCT_SIZE(xfs_dir2_leaf_t, 16); XFS_CHECK_STRUCT_SIZE(xfs_dir2_leaf_tail_t, 4); XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_entry_t, 3); + XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, namelen, 0); + XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, offset, 1); + XFS_CHECK_OFFSET(xfs_dir2_sf_entry_t, name, 3); XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_hdr_t, 10); XFS_CHECK_STRUCT_SIZE(xfs_dir2_sf_off_t, 2);_______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs_______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs
_______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs