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 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 Link: https://lore.kernel.org/all/20260120051114.1281285-1-kartikey406@gmail.com/T/ [v1] Link: https://lore.kernel.org/all/20260121063109.1830263-1-kartikey406@gmail.com/T/ [v2] Signed-off-by: Deepanshu Kartikey --- Changes in v3: - Introduced hfsplus_brec_read_cat() wrapper function for catalog-specific validation instead of modifying generic hfs_brec_read() - Added hfsplus_cat_thread_size() helper to calculate variable-size thread record sizes - Use exact size match (!=) instead of minimum size check (<) - Use sizeof(hfsplus_unichr) instead of hardcoded value 2 - Updated all catalog record read sites to use new wrapper function - Addressed review feedback from Viacheslav Dubeyko Changes in v2: - Use structure initialization (= {0}) instead of memset() - Improved commit message to clarify how uninitialized data is used --- fs/hfsplus/bfind.c | 59 +++++++++++++++++++++++++++++++++++++++++ fs/hfsplus/catalog.c | 4 +-- fs/hfsplus/dir.c | 2 +- fs/hfsplus/hfsplus_fs.h | 3 +++ fs/hfsplus/super.c | 2 +- 5 files changed, 66 insertions(+), 4 deletions(-) diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c index 9b89dce00ee9..fe75f3f2c17a 100644 --- a/fs/hfsplus/bfind.c +++ b/fs/hfsplus/bfind.c @@ -297,3 +297,62 @@ int hfs_brec_goto(struct hfs_find_data *fd, int cnt) fd->bnode = bnode; return res; } + +/** + * hfsplus_cat_thread_size - calculate expected size of a catalog thread record + * @thread: pointer to the thread record + * + * Returns the expected size based on the string length + */ +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); +} + +/** + * 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: + 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 02c1eee4a4b8..6c8380f7208d 100644 --- 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 cadf0b5f9342..d86e2f7b289c 100644 --- 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 45fe3a12ecba..5efb5d176cd9 100644 --- a/fs/hfsplus/hfsplus_fs.h +++ b/fs/hfsplus/hfsplus_fs.h @@ -506,6 +506,9 @@ 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); +u32 hfsplus_cat_thread_size(const struct hfsplus_cat_thread *thread); +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 aaffa9e060a0..e59611a664ef 100644 --- a/fs/hfsplus/super.c +++ b/fs/hfsplus/super.c @@ -567,7 +567,7 @@ 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; -- 2.43.0