hfs: handle more on-disk corruptions without oopsing

hfs seems prone to bad things when it encounters on disk corruption. Many
values are read from disk, and used as lengths to memcpy, as an example.
This patch fixes up several of these problematic cases.

o sanity check the on-disk maximum key lengths on mount
(these are set to a defined value at mkfs time and shouldn't differ)
o check on-disk node keylens against the maximum key length for each tree
o fix hfs_btree_open so that going out via free_tree: doesn't wind
up in hfs_releasepage, which wants to follow the very pointer
we were trying to set up:
HFS_SB(sb)->cat_tree = hfs_btree_open()
...
failure gets to hfs_releasepage and tries
to follow HFS_SB(sb)->cat_tree

Tested with the fsfuzzer; it survives more than it used to.

Signed-off-by: Eric Sandeen <[e-mail]>
Cc: Roman Zippel <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/hfs/bfind.c

···
 		rec = (e + b) / 2;
 		len = hfs_brec_lenoff(bnode, rec, &off);
 		keylen = hfs_brec_keylen(bnode, rec);
+		if (keylen == HFS_BAD_KEYLEN) {
+			res = -EINVAL;
+			goto done;
+		}
 		hfs_bnode_read(bnode, fd->key, off, keylen);
 		cmpval = bnode->tree->keycmp(fd->key, fd->search_key);
 		if (!cmpval) {
···
 	if (rec != e && e >= 0) {
 		len = hfs_brec_lenoff(bnode, e, &off);
 		keylen = hfs_brec_keylen(bnode, e);
+		if (keylen == HFS_BAD_KEYLEN) {
+			res = -EINVAL;
+			goto done;
+		}
 		hfs_bnode_read(bnode, fd->key, off, keylen);
 	}
 done:
···
 
 	len = hfs_brec_lenoff(bnode, fd->record, &off);
 	keylen = hfs_brec_keylen(bnode, fd->record);
+	if (keylen == HFS_BAD_KEYLEN) {
+		res = -EINVAL;
+		goto out;
+	}
 	fd->keyoffset = off;
 	fd->keylength = keylen;
 	fd->entryoffset = off + keylen;

fs/hfs/brec.c

···
 		recoff = hfs_bnode_read_u16(node, node->tree->node_size - (rec + 1) * 2);
 		if (!recoff)
 			return 0;
-		if (node->tree->attributes & HFS_TREE_BIGKEYS)
+		if (node->tree->attributes & HFS_TREE_BIGKEYS) {
 			retval = hfs_bnode_read_u16(node, recoff) + 2;
-		else
+			if (retval > node->tree->max_key_len + 2) {
+				printk(KERN_ERR "hfs: keylen %d too large\n",
+					retval);
+				retval = HFS_BAD_KEYLEN;
+			}
+		} else {
 			retval = (hfs_bnode_read_u8(node, recoff) | 1) + 1;
+			if (retval > node->tree->max_key_len + 1) {
+				printk(KERN_ERR "hfs: keylen %d too large\n",
+					retval);
+				retval = HFS_BAD_KEYLEN;
+			}
+		}
 	}
 	return retval;
 }

fs/hfs/btree.c

···
 		goto fail_page;
 	if (!tree->node_count)
 		goto fail_page;
+	if ((id == HFS_EXT_CNID) && (tree->max_key_len != HFS_MAX_EXT_KEYLEN)) {
+		printk(KERN_ERR "hfs: invalid extent max_key_len %d\n",
+			tree->max_key_len);
+		goto fail_page;
+	}
+	if ((id == HFS_CAT_CNID) && (tree->max_key_len != HFS_MAX_CAT_KEYLEN)) {
+		printk(KERN_ERR "hfs: invalid catalog max_key_len %d\n",
+			tree->max_key_len);
+		goto fail_page;
+	}
+
 	tree->node_size_shift = ffs(size) - 1;
 	tree->pages_per_bnode = (tree->node_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 
···
 	return tree;
 
  fail_page:
-	tree->inode->i_mapping->a_ops = &hfs_aops;
 	page_cache_release(page);
  free_tree:
+	tree->inode->i_mapping->a_ops = &hfs_aops;
 	iput(tree->inode);
 	kfree(tree);
 	return NULL;

fs/hfs/hfs.h

···
 #define HFS_MAX_NAMELEN		128
 #define HFS_MAX_VALENCE		32767U
 
+#define HFS_BAD_KEYLEN		0xFF
+
 /* Meanings of the drAtrb field of the MDB,
  * Reference: _Inside Macintosh: Files_ p. 2-61
  */
···
 	struct hfs_cat_key cat;
 	struct hfs_ext_key ext;
 } hfs_btree_key;
+
+#define HFS_MAX_CAT_KEYLEN	(sizeof(struct hfs_cat_key) - sizeof(u8))
+#define HFS_MAX_EXT_KEYLEN	(sizeof(struct hfs_ext_key) - sizeof(u8))
 
 typedef union hfs_btree_key btree_key;