[PATCH v4] hfsplus: validate thread record before delete key rebuild

[Kyle Zeng <kylebot@openai.com>]

hfsplus_delete_cat() is called with str == NULL when the last open
reference to an unlinked HFS+ hardlink backing inode is closed. In that
case, the function finds the catalog thread by CNID and rebuilds the
catalog key from thread.nodeName.

That reconstruction path reads thread.nodeName.length directly from the
catalog B-tree into fd.search_key and then copies length * 2 bytes into
fd.search_key->cat.name.unicode. It does not first check that the found
record is a thread record, that the record size matches the thread name
length, or that nodeName.length fits in the fixed HFS+ catalog key
buffer.

A corrupted image can therefore provide an oversized thread name length
and make hfs_bnode_read() write past the catalog search-key allocation.

Read the CNID record through hfsplus_brec_read_cat(), which performs the
hfs_brec_find() lookup via hfs_brec_read() before validating the catalog
record. Reject non-thread records before building the delete key from
the validated thread name.

Make hfsplus_brec_read_cat() validate that a thread nodeName length both
fits HFSPLUS_MAX_STRLEN and exactly matches fd->entrylength, then share
the HFS+ thread-record-type helper between hfsplus_find_cat() and
hfsplus_delete_cat().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Kyle Zeng <kylebot@openai.com>
---
 fs/hfsplus/bfind.c      |  8 ++++++--
 fs/hfsplus/catalog.c    | 30 ++++++++++++------------------
 fs/hfsplus/hfsplus_fs.h | 12 ++++++++++++
 3 files changed, 30 insertions(+), 20 deletions(-)

diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
index 9a55fa6d5294..d5e41e1c70b3 100644
--- a/fs/hfsplus/bfind.c
+++ b/fs/hfsplus/bfind.c
@@ -322,8 +322,12 @@ int hfsplus_brec_read_cat(struct hfs_find_data *fd, hfsplus_cat_entry *entry)
 			pr_err("thread record too short (got %u)\n", fd->entrylength);
 			return -EIO;
 		}
-		expected_size = hfsplus_cat_thread_size(&entry->thread);
-		break;
+		if (!is_hfsplus_cat_thread_name_length_valid(&entry->thread,
+							     fd->entrylength)) {
+			pr_err("catalog thread name length corrupted\n");
+			return -EIO;
+		}
+		return 0;
 	default:
 		pr_err("unknown catalog record type %d\n",
 		       be16_to_cpu(entry->type));
diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
index 776ce36cf076..1a4b0beae135 100644
--- a/fs/hfsplus/catalog.c
+++ b/fs/hfsplus/catalog.c
@@ -204,16 +204,11 @@ int hfsplus_find_cat(struct super_block *sb, u32 cnid,
 		return err;
 
 	type = be16_to_cpu(tmp.type);
-	if (type != HFSPLUS_FOLDER_THREAD && type != HFSPLUS_FILE_THREAD) {
+	if (!is_hfs_thread_record_type(type)) {
 		pr_err("found bad thread record in catalog\n");
 		return -EIO;
 	}
 
-	if (be16_to_cpu(tmp.thread.nodeName.length) > 255) {
-		pr_err("catalog name length corrupted\n");
-		return -EIO;
-	}
-
 	hfsplus_cat_build_key_uni(fd->search_key,
 		be32_to_cpu(tmp.thread.parentID),
 		&tmp.thread.nodeName);
@@ -350,23 +345,22 @@ int hfsplus_delete_cat(u32 cnid, struct inode *dir, const struct qstr *str)
 		goto out;
 
 	if (!str) {
-		int len;
+		hfsplus_cat_entry entry = {0};
 
 		hfsplus_cat_build_key_with_cnid(sb, fd.search_key, cnid);
-		err = hfs_brec_find(&fd, hfs_find_rec_by_key);
+		err = hfsplus_brec_read_cat(&fd, &entry);
 		if (err)
 			goto out;
 
-		off = fd.entryoffset +
-			offsetof(struct hfsplus_cat_thread, nodeName);
-		fd.search_key->cat.parent = cpu_to_be32(dir->i_ino);
-		hfs_bnode_read(fd.bnode,
-			&fd.search_key->cat.name.length, off, 2);
-		len = be16_to_cpu(fd.search_key->cat.name.length) * 2;
-		hfs_bnode_read(fd.bnode,
-			&fd.search_key->cat.name.unicode,
-			off + 2, len);
-		fd.search_key->key_len = cpu_to_be16(6 + len);
+		type = be16_to_cpu(entry.type);
+		if (!is_hfs_thread_record_type(type)) {
+			pr_err("found bad thread record in catalog\n");
+			err = -EIO;
+			goto out;
+		}
+
+		hfsplus_cat_build_key_uni(fd.search_key, dir->i_ino,
+					  &entry.thread.nodeName);
 	} else {
 		err = hfsplus_cat_build_key(sb, fd.search_key, dir->i_ino, str);
 		if (unlikely(err))
diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
index ec04b82ad927..01e5f1246ff6 100644
--- a/fs/hfsplus/hfsplus_fs.h
+++ b/fs/hfsplus/hfsplus_fs.h
@@ -521,6 +521,18 @@ static inline u32 hfsplus_cat_thread_size(const struct hfsplus_cat_thread *threa
 	       be16_to_cpu(thread->nodeName.length) * sizeof(hfsplus_unichr);
 }
 
+static inline bool is_hfs_thread_record_type(u16 type)
+{
+	return type == HFSPLUS_FOLDER_THREAD || type == HFSPLUS_FILE_THREAD;
+}
+
+static inline bool is_hfsplus_cat_thread_name_length_valid(
+		const struct hfsplus_cat_thread *thread, u32 entrylength)
+{
+	return be16_to_cpu(thread->nodeName.length) <= HFSPLUS_MAX_STRLEN &&
+	       entrylength == hfsplus_cat_thread_size(thread);
+}
+
 int hfsplus_brec_read_cat(struct hfs_find_data *fd, hfsplus_cat_entry *entry);
 
 /*
-- 
2.54.0