erofs: avoid infinite loops due to corrupted subpage compact indexes

Robert reported an infinite loop observed by two crafted images.

The root cause is that `clusterofs` can be larger than `lclustersize`
for !NONHEAD `lclusters` in corrupted subpage compact indexes, e.g.:

blocksize = lclustersize = 512 lcn = 6 clusterofs = 515

Move the corresponding check for full compress indexes to
`z_erofs_load_lcluster_from_disk()` to also cover subpage compact
compress indexes.

It also fixes the position of `m->type >= Z_EROFS_LCLUSTER_TYPE_MAX`
check, since it should be placed right after
`z_erofs_load_{compact,full}_lcluster()`.

Fixes: 8d2517aaeea3 ("erofs: fix up compacted indexes for block size < 4096")
Fixes: 1a5223c182fd ("erofs: do sanity check on m->type in z_erofs_load_compact_lcluster()")
Reported-by: Robert Morris <[e-mail]>
Closes: https://lore.kernel.org/r/35167.1760645886@localhost
Reviewed-by: Hongbo Li <[e-mail]>
Signed-off-by: Gao Xiang <[e-mail]>

fs/erofs/zmap.c

···
 	} else {
 		m->partialref = !!(advise & Z_EROFS_LI_PARTIAL_REF);
 		m->clusterofs = le16_to_cpu(di->di_clusterofs);
-		if (m->clusterofs >= 1 << vi->z_lclusterbits) {
-			DBG_BUGON(1);
-			return -EFSCORRUPTED;
-		}
 		m->pblk = le32_to_cpu(di->di_u.blkaddr);
 	}
 	return 0;
···
 static int z_erofs_load_lcluster_from_disk(struct z_erofs_maprecorder *m,
 					   unsigned int lcn, bool lookahead)
 {
+	struct erofs_inode *vi = EROFS_I(m->inode);
+	int err;
+
+	if (vi->datalayout == EROFS_INODE_COMPRESSED_COMPACT) {
+		err = z_erofs_load_compact_lcluster(m, lcn, lookahead);
+	} else {
+		DBG_BUGON(vi->datalayout != EROFS_INODE_COMPRESSED_FULL);
+		err = z_erofs_load_full_lcluster(m, lcn);
+	}
+	if (err)
+		return err;
+
 	if (m->type >= Z_EROFS_LCLUSTER_TYPE_MAX) {
 		erofs_err(m->inode->i_sb, "unknown type %u @ lcn %u of nid %llu",
-				m->type, lcn, EROFS_I(m->inode)->nid);
+			  m->type, lcn, EROFS_I(m->inode)->nid);
 		DBG_BUGON(1);
 		return -EOPNOTSUPP;
+	} else if (m->type != Z_EROFS_LCLUSTER_TYPE_NONHEAD &&
+		   m->clusterofs >= (1 << vi->z_lclusterbits)) {
+		DBG_BUGON(1);
+		return -EFSCORRUPTED;
 	}
-
-	switch (EROFS_I(m->inode)->datalayout) {
-	case EROFS_INODE_COMPRESSED_FULL:
-		return z_erofs_load_full_lcluster(m, lcn);
-	case EROFS_INODE_COMPRESSED_COMPACT:
-		return z_erofs_load_compact_lcluster(m, lcn, lookahead);
-	default:
-		return -EINVAL;
-	}
+	return 0;
 }
 
 static int z_erofs_extent_lookback(struct z_erofs_maprecorder *m,