hfsplus: fix uninit-value by validating catalog record size

Syzbot reported a KMSAN uninit-value issue in hfsplus_strcasecmp(). The
root cause is that hfs_brec_read() doesn't validate that the on-disk
record size matches the expected size for the record type being read.

When mounting a corrupted filesystem, hfs_brec_read() may read less data
than expected. For example, when reading a catalog thread record, the
debug output showed:

  HFSPLUS_BREC_READ: rec_len=520, fd->entrylength=26
  HFSPLUS_BREC_READ: WARNING - entrylength (26) < rec_len (520) - PARTIAL READ!

hfs_brec_read() only validates that entrylength is not greater than the
buffer size, but doesn't check if it's less than expected. It successfully
reads 26 bytes into a 520-byte structure and returns success, leaving 494
bytes uninitialized.

This uninitialized data in tmp.thread.nodeName then gets copied by
hfsplus_cat_build_key_uni() and used by hfsplus_strcasecmp(), triggering
the KMSAN warning when the uninitialized bytes are used as array indices
in case_fold().

Fix by introducing hfsplus_brec_read_cat() wrapper that:
1. Calls hfs_brec_read() to read the data
2. Validates the record size based on the type field:
   - Fixed size for folder and file records
   - Variable size for thread records (depends on string length)
3. Returns -EIO if size doesn't match expected

For thread records, check against HFSPLUS_MIN_THREAD_SZ before reading
nodeName.length to avoid reading uninitialized data at call sites that
don't zero-initialize the entry structure.

Also initialize the tmp variable in hfsplus_find_cat() as defensive
programming to ensure no uninitialized data even if validation is
bypassed.

Reported-by: syzbot+d80abb5b890d39261e72@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=d80abb5b890d39261e72
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Tested-by: syzbot+d80abb5b890d39261e72@syzkaller.appspotmail.com
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Tested-by: Viacheslav Dubeyko <slava@dubeyko.com>
Suggested-by: Charalampos Mitrodimas <charmitro@posteo.net>
Link: https://lore.kernel.org/all/20260120051114.1281285-1-kartikey406@gmail.com/
Link: https://lore.kernel.org/all/20260121063109.1830263-1-kartikey406@gmail.com/
Link: https://lore.kernel.org/all/20260212014233.2422046-1-kartikey406@gmail.com/
Link: https://lore.kernel.org/all/20260214002100.436125-1-kartikey406@gmail.com/T/
Link: https://lore.kernel.org/all/20260221061626.15853-1-kartikey406@gmail.com/T/
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20260307010302.41547-1-kartikey406@gmail.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
index 336d654861c5974e55a8e751044c4e0ac0c66a86..9a55fa6d529429b806e5947a4b751486ce0678e1 100644 (file)
--- a/fs/hfsplus/bfind.c
+++ b/fs/hfsplus/bfind.c
@@ -287,3 +287,54 @@ out:
        fd->bnode = bnode;
        return res;
 }
+
+/**
+ * hfsplus_brec_read_cat - read and validate a catalog record
+ * @fd: find data structure
+ * @entry: pointer to catalog entry to read into
+ *
+ * Reads a catalog record and validates its size matches the expected
+ * size based on the record type.
+ *
+ * Returns 0 on success, or negative error code on failure.
+ */
+int hfsplus_brec_read_cat(struct hfs_find_data *fd, hfsplus_cat_entry *entry)
+{
+       int res;
+       u32 expected_size;
+
+       res = hfs_brec_read(fd, entry, sizeof(hfsplus_cat_entry));
+       if (res)
+               return res;
+
+       /* Validate catalog record size based on type */
+       switch (be16_to_cpu(entry->type)) {
+       case HFSPLUS_FOLDER:
+               expected_size = sizeof(struct hfsplus_cat_folder);
+               break;
+       case HFSPLUS_FILE:
+               expected_size = sizeof(struct hfsplus_cat_file);
+               break;
+       case HFSPLUS_FOLDER_THREAD:
+       case HFSPLUS_FILE_THREAD:
+               /* Ensure we have at least the fixed fields before reading nodeName.length */
+               if (fd->entrylength < HFSPLUS_MIN_THREAD_SZ) {
+                       pr_err("thread record too short (got %u)\n", fd->entrylength);
+                       return -EIO;
+               }
+               expected_size = hfsplus_cat_thread_size(&entry->thread);
+               break;
+       default:
+               pr_err("unknown catalog record type %d\n",
+                      be16_to_cpu(entry->type));
+               return -EIO;
+       }
+
+       if (fd->entrylength != expected_size) {
+               pr_err("catalog record size mismatch (type %d, got %u, expected %u)\n",
+                      be16_to_cpu(entry->type), fd->entrylength, expected_size);
+               return -EIO;
+       }
+
+       return 0;
+}

diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
index eef7412a4d58bcfb040ada5a9e4bf4df0ed70815..708046c5dae62eb2736d002b85d81584eb5f6492 100644 (file)
--- a/fs/hfsplus/catalog.c
+++ b/fs/hfsplus/catalog.c
@@ -194,12 +194,12 @@ static int hfsplus_fill_cat_thread(struct super_block *sb,
 int hfsplus_find_cat(struct super_block *sb, u32 cnid,
                     struct hfs_find_data *fd)
 {
-       hfsplus_cat_entry tmp;
+       hfsplus_cat_entry tmp = {0};
        int err;
        u16 type;
 
        hfsplus_cat_build_key_with_cnid(sb, fd->search_key, cnid);
-       err = hfs_brec_read(fd, &tmp, sizeof(hfsplus_cat_entry));
+       err = hfsplus_brec_read_cat(fd, &tmp);
        if (err)
                return err;
 

diff --git a/fs/hfsplus/dir.c b/fs/hfsplus/dir.c
index 9f0345bf1b5aa0c870d093eff40a23f5fc5aa9f4..6059bd59d66e59841664e65c53e71b84bdd6bf3b 100644 (file)
--- a/fs/hfsplus/dir.c
+++ b/fs/hfsplus/dir.c
@@ -49,7 +49,7 @@ static struct dentry *hfsplus_lookup(struct inode *dir, struct dentry *dentry,
        if (unlikely(err < 0))
                goto fail;
 again:
-       err = hfs_brec_read(&fd, &entry, sizeof(entry));
+       err = hfsplus_brec_read_cat(&fd, &entry);
        if (err) {
                if (err == -ENOENT) {
                        hfs_find_exit(&fd);

diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
index 122ab57193bbec584b0d91a448753fb4de2070a3..420dc920e097ef7d4cbc1ec371df93974fbecbfa 100644 (file)
--- a/fs/hfsplus/hfsplus_fs.h
+++ b/fs/hfsplus/hfsplus_fs.h
@@ -516,6 +516,15 @@ int hfsplus_submit_bio(struct super_block *sb, sector_t sector, void *buf,
                       void **data, blk_opf_t opf);
 int hfsplus_read_wrapper(struct super_block *sb);
 
+static inline u32 hfsplus_cat_thread_size(const struct hfsplus_cat_thread *thread)
+{
+       return offsetof(struct hfsplus_cat_thread, nodeName) +
+              offsetof(struct hfsplus_unistr, unicode) +
+              be16_to_cpu(thread->nodeName.length) * sizeof(hfsplus_unichr);
+}
+
+int hfsplus_brec_read_cat(struct hfs_find_data *fd, hfsplus_cat_entry *entry);
+
 /*
  * time helpers: convert between 1904-base and 1970-base timestamps
  *

diff --git a/fs/hfsplus/super.c b/fs/hfsplus/super.c
index 2a135c78d0b2dc94520216b8f06fa82a4b2c47e9..242ccca3acb7c2a7c6bb3279a71fdf85bafafcfe 100644 (file)
--- a/fs/hfsplus/super.c
+++ b/fs/hfsplus/super.c
@@ -571,7 +571,7 @@ static int hfsplus_fill_super(struct super_block *sb, struct fs_context *fc)
        err = hfsplus_cat_build_key(sb, fd.search_key, HFSPLUS_ROOT_CNID, &str);
        if (unlikely(err < 0))
                goto out_put_root;
-       if (!hfs_brec_read(&fd, &entry, sizeof(entry))) {
+       if (!hfsplus_brec_read_cat(&fd, &entry)) {
                hfs_find_exit(&fd);
                if (entry.type != cpu_to_be16(HFSPLUS_FOLDER)) {
                        err = -EIO;