[PATCH 7/7] libext2fs: enforce the block group descriptor size in ext2fs_open()

[Theodore Ts'o <tytso@mit.edu>]

Since various parts of the library depend on the value of s_desc_size,
check to make sure it is the correct, expected value based on the file
system features.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
 lib/ext2fs/ext2_err.et.in |  3 +++
 lib/ext2fs/openfs.c       | 15 +++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/lib/ext2fs/ext2_err.et.in b/lib/ext2fs/ext2_err.et.in
index ccf1894..5987185 100644
--- a/lib/ext2fs/ext2_err.et.in
+++ b/lib/ext2fs/ext2_err.et.in
@@ -443,4 +443,7 @@ ec	EXT2_ET_MMP_CHANGE_ABORT,
 ec	EXT2_ET_MMP_OPEN_DIRECT,
 	"MMP: open with O_DIRECT failed"
 
+ec	EXT2_ET_BAD_DESC_SIZE,
+	"Block group descriptor size incorrect"
+
 	end
diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 482e4ab..fbe9acd 100644
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -263,6 +263,21 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
 		retval = EXT2_ET_CORRUPT_SUPERBLOCK;
 		goto cleanup;
 	}
+
+	/* Enforce the block group descriptor size */
+	if (fs->super->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) {
+		if (fs->super->s_desc_size != EXT2_MIN_DESC_SIZE_64BIT) {
+			retval = EXT2_ET_BAD_DESC_SIZE;
+			goto cleanup;
+		}
+	} else {
+		if (fs->super->s_desc_size &&
+		    fs->super->s_desc_size != EXT2_MIN_DESC_SIZE) {
+			retval = EXT2_ET_BAD_DESC_SIZE;
+			goto cleanup;
+		}
+	}
+
 	fs->cluster_ratio_bits = fs->super->s_log_cluster_size -
 		fs->super->s_log_block_size;
 	if (EXT2_BLOCKS_PER_GROUP(fs->super) !=
-- 
1.7.12.rc0.22.gcdd159b