From: Baokun Li <libaokun1@xxxxxxxxxx> The maximum length of a filename is 255 and the minimum block size is 1024, so it is always guaranteed that the number of entries is greater than or equal to 2 when do_split() is called. So unless ext4_dx_add_entry() and make_indexed_dir() or some other functions are buggy, 'split == 0' will not occur. Setting 'continued' to 0 in this case masks the problem that the file system has become corrupted, even though it prevents possible out-of-bounds access. Hence WARN_ON_ONCE() is used to check if 'split' is 0, and if it is then warns and returns an error to abort split. Suggested-by: Theodore Ts'o <tytso@xxxxxxx> Link: https://lore.kernel.org/r/20240823160518.GA424729@xxxxxxx Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx> --- fs/ext4/namei.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index 790db7eac6c2..08d15cd2b594 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -2000,8 +2000,17 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir, else split = count/2; + if (WARN_ON_ONCE(split == 0)) { + /* Should never happen, but avoid out-of-bounds access below */ + ext4_error_inode_block(dir, (*bh)->b_blocknr, 0, + "bad indexed directory? hash=%08x:%08x count=%d move=%u", + hinfo->hash, hinfo->minor_hash, count, move); + err = -EFSCORRUPTED; + goto out; + } + hash2 = map[split].hash; - continued = split > 0 ? hash2 == map[split - 1].hash : 0; + continued = hash2 == map[split - 1].hash; dxtrace(printk(KERN_INFO "Split block %lu at %x, %i/%i\n", (unsigned long)dx_get_block(frame->at), hash2, split, count-split)); @@ -2043,10 +2052,11 @@ static struct ext4_dir_entry_2 *do_split(handle_t *handle, struct inode *dir, return de; journal_error: + ext4_std_error(dir->i_sb, err); +out: brelse(*bh); brelse(bh2); *bh = NULL; - ext4_std_error(dir->i_sb, err); return ERR_PTR(err); } -- 2.46.1
