[LU-14710] check_dot() does not handle dirdata/FID entry properly

Related — Mon, 14 Nov 2022 16:24:00 +0000

In check_dot() it assumes that the "." and ".." entries are fixed at 12-bytes, but with the dirdata feature storing a FID in these directory entries, they will be larger. If there is some unrelated problem in the directory returned by e2fsck_check_dirent_data() then this check will incorrectly cause the "." and ".." entries to be recreated and clobber the FIDs.

static int check_dot(...)
{
        :
        dir_data_error = e2fsck_check_dirent_data(ctx, dirent, offset, pctx);
        :
        if (rec_len > 12) {
                new_len = rec_len - 12;
                if (new_len > 12 && dir_data_error) {
                        if (created ||
                            fix_problem(ctx, PR_2_SPLIT_DOT, pctx)) {
                                nextdir = (struct ext2_dir_entry *)
                                        ((char *) dirent + 12);
                                dirent->rec_len = 12;
                                (void) ext2fs_set_rec_len(ctx->fs, new_len,
                                                          nextdir);
                                nextdir->inode = 0;
                                ext2fs_dirent_set_name_len(nextdir, 0);
                                ext2fs_dirent_set_file_type(nextdir,
                                                            EXT2_FT_UNKNOWN);

As a follow-on, the HTree index will no longer immediately follow the ".." entry (fake_root) and be invalidated:

Directory entry for '.' in ... (1032783) is big.
Split? no
Second entry '3.3.0' (inode=538027 fid=[0x380020941:0x4c38:0x0]) in directory inode 1032783 should be '..'
Fix? no

The code in check_dot() needs to be updated to properly check for the length of dirdata entries.

It doesn't look like same bug appears in check_dotdot(). It is checking for (rec_len < 12), which should be OK, since dirdata entries will always be larger. Properly accounting for rec_len in check_dot() should avoid any problems in check_dotdot(). However, there is LU-7399 which suggests an improvement for rebuilding ".." in other situations.

Whamcloud Community JIRA

[LU-14710] check_dot() does not handle dirdata/FID entry properly