[PATCH v6 1/2] hfs: initialize B-tree inodes and validate catalog CNIDs

[yangguikun <yangguikun19@qq.com>]

hfs_btree_open() leaves the internal B-tree inodes with i_mode == 0.
A crafted catalog record naming CNID 3 or 4 can return one of these
cached inodes through hfs_iget(), triggering VFS_BUG_ON_INODE() in
may_open() with CONFIG_DEBUG_VFS=y.

Initialize the B-tree inodes with S_IFREG and their address-space
operations before publishing them. Reject attempts to reuse an
already-cached B-tree inode.

Validate catalog CNIDs and record types before the inode-cache lookup,
since cached inodes bypass hfs_read_inode() validation. This also
prevents a crafted file record from aliasing the root directory inode.

Found by syzkaller-style fuzzing of v7.2-rc7.

Suggested-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/linux-fsdevel/tencent_24D928451FEFA8A35482EFFA9132A7305307@qq.com/
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: yangguikun <yangguikun19@qq.com>
---
Changes in v6:
 - Drop set_nlink() and tz_secondswest initialization for B-tree inodes.
 - Use WARN_ON_ONCE() for an already-cached B-tree inode.
 - Defer hfs_iget() error propagation to a separate patch.

diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
index 41b4e8f..1891ad5 100644
--- a/fs/hfs/btree.c
+++ b/fs/hfs/btree.c
@@ -155,44 +155,9 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id, btree_keycmp ke
 	tree->cnid = id;
 	tree->keycmp = keycmp;
 
-	tree->inode = iget_locked(sb, id);
-	if (!tree->inode)
+	tree->inode = hfs_system_iget(sb, id);
+	if (IS_ERR(tree->inode))
 		goto free_tree;
-	BUG_ON(!(inode_state_read_once(tree->inode) & I_NEW));
-	{
-	struct hfs_mdb *mdb = HFS_SB(sb)->mdb;
-	HFS_I(tree->inode)->flags = 0;
-	mutex_init(&HFS_I(tree->inode)->extents_lock);
-	switch (id) {
-	case HFS_EXT_CNID:
-		hfs_inode_read_fork(tree->inode, mdb->drXTExtRec, mdb->drXTFlSize,
-				    mdb->drXTFlSize, be32_to_cpu(mdb->drXTClpSiz));
-		if (HFS_I(tree->inode)->alloc_blocks >
-					HFS_I(tree->inode)->first_blocks) {
-			pr_err("invalid btree extent records\n");
-			unlock_new_inode(tree->inode);
-			goto free_inode;
-		}
-
-		tree->inode->i_mapping->a_ops = &hfs_btree_aops;
-		break;
-	case HFS_CAT_CNID:
-		hfs_inode_read_fork(tree->inode, mdb->drCTExtRec, mdb->drCTFlSize,
-				    mdb->drCTFlSize, be32_to_cpu(mdb->drCTClpSiz));
-
-		if (!HFS_I(tree->inode)->first_blocks) {
-			pr_err("invalid btree extent records (0 size)\n");
-			unlock_new_inode(tree->inode);
-			goto free_inode;
-		}
-
-		tree->inode->i_mapping->a_ops = &hfs_btree_aops;
-		break;
-	default:
-		BUG();
-	}
-	}
-	unlock_new_inode(tree->inode);
 
 	mapping = tree->inode->i_mapping;
 	folio = filemap_grab_folio(mapping, 0);
diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
index e250f87..8d52170 100644
--- a/fs/hfs/hfs_fs.h
+++ b/fs/hfs/hfs_fs.h
@@ -163,6 +163,11 @@ extern int hfs_cat_move(u32 cnid, struct inode *src_dir,
 extern void hfs_cat_build_key(struct super_block *sb, btree_key *key,
 			      u32 parent, const struct qstr *name);
 
+static inline bool hfs_is_system_reserved_cnid(u32 cnid)
+{
+	return cnid > HFS_ROOT_CNID && cnid < HFS_FIRSTUSER_CNID;
+}
+
 /*
  * Validate the CNID of a catalog record.
  */
@@ -219,6 +224,7 @@ extern void hfs_inode_read_fork(struct inode *inode, struct hfs_extent *ext,
 				u32 clump_size);
 extern struct inode *hfs_iget(struct super_block *sb, struct hfs_cat_key *key,
 				hfs_cat_rec *rec);
+extern struct inode *hfs_system_iget(struct super_block *sb, u32 cnid);
 extern void hfs_evict_inode(struct inode *inode);
 extern void hfs_delete_inode(struct inode *inode);
 
diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index 2aef3c3..a66de7b 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -421,6 +421,69 @@ static int hfs_read_inode(struct inode *inode, void *data)
 	return 0;
 }
 
+static int hfs_system_read_inode(struct inode *inode)
+{
+	struct hfs_sb_info *hsb = HFS_SB(inode->i_sb);
+	struct hfs_mdb *mdb = hsb->mdb;
+
+	HFS_I(inode)->flags = 0;
+	HFS_I(inode)->rsrc_inode = NULL;
+	mutex_init(&HFS_I(inode)->extents_lock);
+
+	inode->i_uid = hsb->s_uid;
+	inode->i_gid = hsb->s_gid;
+
+	inode->i_mode = S_IFREG;
+	inode->i_mapping->a_ops = &hfs_btree_aops;
+
+	switch (inode->i_ino) {
+	case HFS_EXT_CNID:
+		hfs_inode_read_fork(inode, mdb->drXTExtRec, mdb->drXTFlSize,
+				    mdb->drXTFlSize, be32_to_cpu(mdb->drXTClpSiz));
+		if (HFS_I(inode)->alloc_blocks > HFS_I(inode)->first_blocks) {
+			pr_err("invalid btree extent records\n");
+			return -EIO;
+		}
+		break;
+	case HFS_CAT_CNID:
+		hfs_inode_read_fork(inode, mdb->drCTExtRec, mdb->drCTFlSize,
+				    mdb->drCTFlSize, be32_to_cpu(mdb->drCTClpSiz));
+		if (!HFS_I(inode)->first_blocks) {
+			pr_err("invalid btree extent records (0 size)\n");
+			return -EIO;
+		}
+		break;
+	default:
+		return -EIO;
+	}
+
+	return 0;
+}
+
+struct inode *hfs_system_iget(struct super_block *sb, u32 cnid)
+{
+	struct inode *inode;
+	int err;
+
+	inode = iget_locked(sb, cnid);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	if (WARN_ON_ONCE(!(inode_state_read_once(inode) & I_NEW))) {
+		iput(inode);
+		return ERR_PTR(-EEXIST);
+	}
+
+	err = hfs_system_read_inode(inode);
+	if (err) {
+		iget_failed(inode);
+		return ERR_PTR(err);
+	}
+
+	unlock_new_inode(inode);
+	return inode;
+}
+
 /*
  * __hfs_iget()
  *
@@ -446,6 +509,11 @@ struct inode *hfs_iget(struct super_block *sb, struct hfs_cat_key *key, hfs_cat_
 	default:
 		return NULL;
 	}
+
+	if (!hfs_is_valid_cnid(cnid, rec->type) ||
+	    hfs_is_system_reserved_cnid(cnid))
+		return NULL;
+
 	inode = iget5_locked(sb, cnid, hfs_test_inode, hfs_read_inode, &data);
 	if (inode && (inode_state_read_once(inode) & I_NEW))
 		unlock_new_inode(inode);
-- 
2.53.0.windows.1