fsck.cramfs: fix crash when superblock size is too small

This hopefully fixes the original problem addressed by the reverted
patch 7cb962c7.

The bug was introduced by myself in
    f991dbd3 "fsck.cramfs: allow smaller superblock sizes"

CC: Tobias Stoeckmann <tobias@stoeckmann.org>
Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>

disk-utils/fsck.cramfs.c

@@ -192,7 +192,7 @@ static void test_super(int *start, size_t * length)
 		errx(FSCK_EX_ERROR, _("unsupported filesystem features"));
 
 	/* What are valid superblock sizes? */
-	if (super.size < sizeof(struct cramfs_super))
+	if (super.size < *start + sizeof(struct cramfs_super))
 		errx(FSCK_EX_UNCORRECTED, _("superblock size (%d) too small"),
 		     super.size);
 

tests/expected/cramfs/fsck-bad-header

@@ -1,2 +1 @@
-fsck.cramfs: file extends past end of filesystem
-fsck.cramfs: crc error
+fsck.cramfs: superblock size (76) too small

tests/ts/cramfs/fsck-bad-header

@@ -16,7 +16,7 @@
 # GNU General Public License for more details.
 #
 TS_TOPDIR="${0%/*}/../.."
-TS_DESC="fsck endianness"
+TS_DESC="fsck bad header"
 
 . $TS_TOPDIR/functions.sh
 ts_init "$*"