debugfs, e2fsck: fix s_desc_size handling

The s_desc_size in the superblock specifies the group descriptor
size in bytes, but in various places the EXT4_FEATURE_INCOMPAT_64BIT
flag implies that the descriptor size is EXT2_MIN_DESC_SIZE_64BIT
(64 bytes) instead of checking the actual size.  In other places,
the s_desc_size field is used without checking for INCOMPAT_64BIT.

In the case of ext2fs_group_desc() the s_desc_size was being ignored,
and assumed to be sizeof(struct ext4_group_desc), which would result
in garbage for any but the first group descriptor.  Similarly, in
ext2fs_group_desc_csum() and print_csum() they assumed that the
maximum group descriptor size was sizeof(struct ext4_group_desc).
Fix these functions to use the actual superblock s_desc_size if
INCOMPAT_64BIT.

Conversely, in ext2fs_swap_group_desc2() s_desc_size was used
without checking for INCOMPAT_64BIT being set.

The e2fsprogs behaviour is different than that of the kernel,
which always checks INCOMPAT_64BIT, and only uses s_desc_size to
determine the offset of group descriptors and what range of bytes
to checksum.

Allow specifying the s_desc_size field at mke2fs time with the
"-E desc_size=NNN" option.  Allow a power-of-two s_desc_size
value up to s_blocksize if INCOMPAT_64BIT is specified.  This
is not expected to be used by regular users at this time, so it
is not currently documented in the mke2fs usage or man page.

Add m_desc_size_128, f_desc_size_128, and f_desc_bad test cases to
verify mke2fs and e2fsck handling of larger group descriptor sizes.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 7 insertions, 4 deletions

diff --git a/debugfs/set_fields.c b/debugfs/set_fields.c
index 064de395..9c3b0001 100644
--- a/debugfs/set_fields.c
+++ b/debugfs/set_fields.c
@@ -702,11 +702,14 @@ void do_set_block_group_descriptor(int argc, char *argv[])
 	int			size;
 
 	/*
-	 *Determine whether we are editing an ext2 or ext4 block
-	 * group descriptor
+	 * Determine whether we are editing an ext2 or ext4 block group
+	 * descriptor.  Descriptors larger than ext4_group_desc cannot
+	 * have their fields edited yet, because they do not have any
+	 * names assigned.  When that happens, this function needs to
+	 * be updated for the new descriptor struct and fields.
 	 */
-	if (current_fs && current_fs->super->s_feature_incompat &
-	    EXT4_FEATURE_INCOMPAT_64BIT) {
+	if (current_fs &&
+	    EXT2_DESC_SIZE(current_fs->super) >= EXT2_MIN_DESC_SIZE_64BIT) {
 		table = ext4_bg_fields;
 		edit = &set_gd4;
 		size = sizeof(set_gd4);