hfs: prevent btree data loss on ENOSPC

Inserting a new record in a btree may require splitting several of its
nodes.  If we hit ENOSPC halfway through, the new nodes will be left
orphaned and their records will be lost.  This could mean lost inodes or
extents.

Henceforth, check the available disk space before making any changes.
This still leaves the potential problem of corruption on ENOMEM.

There is no need to reserve space before deleting a catalog record, as we
do for hfsplus.  This difference is because hfs index nodes have fixed
length keys.

Link: http://lkml.kernel.org/r/ab5fc8a7d5ffccfd5f27b1cf2cb4ceb6c110da74.1536269131.git.ernesto.mnd.fernandez@gmail.com
Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfs/btree.c

@@ -220,25 +220,17 @@ static struct hfs_bnode *hfs_bmap_new_bmap(struct hfs_bnode *prev, u32 idx)
 	return node;
 }
 
-struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree)
+/* Make sure @tree has enough space for the @rsvd_nodes */
+int hfs_bmap_reserve(struct hfs_btree *tree, int rsvd_nodes)
 {
-	struct hfs_bnode *node, *next_node;
-	struct page **pagep;
-	u32 nidx, idx;
-	unsigned off;
-	u16 off16;
-	u16 len;
-	u8 *data, byte, m;
-	int i;
-
-	while (!tree->free_nodes) {
-		struct inode *inode = tree->inode;
-		u32 count;
-		int res;
+	struct inode *inode = tree->inode;
+	u32 count;
+	int res;
 
+	while (tree->free_nodes < rsvd_nodes) {
 		res = hfs_extend_file(inode);
 		if (res)
-			return ERR_PTR(res);
+			return res;
 		HFS_I(inode)->phys_size = inode->i_size =
 				(loff_t)HFS_I(inode)->alloc_blocks *
 				HFS_SB(tree->sb)->alloc_blksz;
@@ -246,9 +238,26 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree)
 					  tree->sb->s_blocksize_bits;
 		inode_set_bytes(inode, inode->i_size);
 		count = inode->i_size >> tree->node_size_shift;
-		tree->free_nodes = count - tree->node_count;
+		tree->free_nodes += count - tree->node_count;
 		tree->node_count = count;
 	}
+	return 0;
+}
+
+struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree)
+{
+	struct hfs_bnode *node, *next_node;
+	struct page **pagep;
+	u32 nidx, idx;
+	unsigned off;
+	u16 off16;
+	u16 len;
+	u8 *data, byte, m;
+	int i, res;
+
+	res = hfs_bmap_reserve(tree, 1);
+	if (res)
+		return ERR_PTR(res);
 
 	nidx = 0;
 	node = hfs_bnode_find(tree, nidx);

fs/hfs/btree.h

@@ -82,6 +82,7 @@ struct hfs_find_data {
 extern struct hfs_btree *hfs_btree_open(struct super_block *, u32, btree_keycmp);
 extern void hfs_btree_close(struct hfs_btree *);
 extern void hfs_btree_write(struct hfs_btree *);
+extern int hfs_bmap_reserve(struct hfs_btree *, int);
 extern struct hfs_bnode * hfs_bmap_alloc(struct hfs_btree *);
 extern void hfs_bmap_free(struct hfs_bnode *node);
 

fs/hfs/catalog.c

@@ -97,6 +97,14 @@ int hfs_cat_create(u32 cnid, struct inode *dir, const struct qstr *str, struct i
 	if (err)
 		return err;
 
+	/*
+	 * Fail early and avoid ENOSPC during the btree operations. We may
+	 * have to split the root node at most once.
+	 */
+	err = hfs_bmap_reserve(fd.tree, 2 * fd.tree->depth);
+	if (err)
+		goto err2;
+
 	hfs_cat_build_key(sb, fd.search_key, cnid, NULL);
 	entry_size = hfs_cat_build_thread(sb, &entry, S_ISDIR(inode->i_mode) ?
 			HFS_CDR_THD : HFS_CDR_FTH,
@@ -295,6 +303,14 @@ int hfs_cat_move(u32 cnid, struct inode *src_dir, const struct qstr *src_name,
 		return err;
 	dst_fd = src_fd;
 
+	/*
+	 * Fail early and avoid ENOSPC during the btree operations. We may
+	 * have to split the root node at most once.
+	 */
+	err = hfs_bmap_reserve(src_fd.tree, 2 * src_fd.tree->depth);
+	if (err)
+		goto out;
+
 	/* find the old dir entry and read the data */
 	hfs_cat_build_key(sb, src_fd.search_key, src_dir->i_ino, src_name);
 	err = hfs_brec_find(&src_fd);

fs/hfs/extent.c

@@ -117,6 +117,10 @@ static int __hfs_ext_write_extent(struct inode *inode, struct hfs_find_data *fd)
 	if (HFS_I(inode)->flags & HFS_FLG_EXT_NEW) {
 		if (res != -ENOENT)
 			return res;
+		/* Fail early and avoid ENOSPC during the btree operation */
+		res = hfs_bmap_reserve(fd->tree, fd->tree->depth + 1);
+		if (res)
+			return res;
 		hfs_brec_insert(fd, HFS_I(inode)->cached_extents, sizeof(hfs_extent_rec));
 		HFS_I(inode)->flags &= ~(HFS_FLG_EXT_DIRTY|HFS_FLG_EXT_NEW);
 	} else {