In a discussion over a proposed patch, "ext4: replace strcpy() with '.' assignment"[1], I had asserted that directory entries in ext4 were not NUL terminated, and hence it was safe to replace strcpy() with a direct assignment. As it turns out, this was incorrect. It's true for all all directory entries *except* for '.' and '..' where the kernel was using strcmp() and where e2fsck actually checks and offers to fix things if '.' and '..' are not NUL terminated.
[1] https://lore.kernel.org/r/202505191316.jjmnpobo-...@intel.com We can't change this without breaking old kernel versions, but in the spirit of "be liberal in what you receive", use direct comparison of de->name_len and de->name[0,1] instead of strcmp(). This has the side benefit of reducing the compiled text size by 96 bytes on x86_64. Signed-off-by: Theodore Ts'o <ty...@mit.edu> --- fs/ext4/namei.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index a178ac229489..b82f5841c65a 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -3082,7 +3082,8 @@ bool ext4_empty_dir(struct inode *inode) de = (struct ext4_dir_entry_2 *) bh->b_data; if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size, 0) || - le32_to_cpu(de->inode) != inode->i_ino || strcmp(".", de->name)) { + le32_to_cpu(de->inode) != inode->i_ino || de->name_len != 1 || + de->name[0] != '.') { ext4_warning_inode(inode, "directory missing '.'"); brelse(bh); return false; @@ -3091,7 +3092,8 @@ bool ext4_empty_dir(struct inode *inode) de = ext4_next_entry(de, sb->s_blocksize); if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size, offset) || - le32_to_cpu(de->inode) == 0 || strcmp("..", de->name)) { + le32_to_cpu(de->inode) == 0 || de->name_len != 2 || + de->name[0] != '.' || de->name[1] != '.') { ext4_warning_inode(inode, "directory missing '..'"); brelse(bh); return false; @@ -3532,7 +3534,7 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle, if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size, 0) || le32_to_cpu(de->inode) != inode->i_ino || - strcmp(".", de->name)) { + de->name_len != 1 || de->name[0] != '.') { EXT4_ERROR_INODE(inode, "directory missing '.'"); brelse(bh); *retval = -EFSCORRUPTED; @@ -3543,7 +3545,8 @@ static struct buffer_head *ext4_get_first_dir_block(handle_t *handle, de = ext4_next_entry(de, inode->i_sb->s_blocksize); if (ext4_check_dir_entry(inode, NULL, de, bh, bh->b_data, bh->b_size, offset) || - le32_to_cpu(de->inode) == 0 || strcmp("..", de->name)) { + le32_to_cpu(de->inode) == 0 || de->name_len != 2 || + de->name[0] != '.' || de->name[1] != '.') { EXT4_ERROR_INODE(inode, "directory missing '..'"); brelse(bh); *retval = -EFSCORRUPTED; -- 2.47.2
