On Mon 29-03-21 17:20:35, Zhang Yi wrote: > On 2021/3/23 1:25, Jan Kara wrote: > > Hi! > > > > On Mon 22-03-21 23:24:23, Zhang Yi wrote: > >> We find a use after free problem when CONFIG_QUOTA is enabled, the detail of > >> this problem is below. > >> > >> mount_bdev() > >> ext4_fill_super() > >> sb->s_root = d_make_root(root); > >> ext4_orphan_cleanup() > >> sb->s_flags |= SB_ACTIVE; <--- 1. mark sb active > >> ext4_orphan_get() > >> ext4_truncate() > >> ext4_block_truncate_page() > >> mark_buffer_dirty <--- 2. dirty inode > >> iput() > >> iput_final <--- 3. put into lru list > >> ext4_mark_recovery_complete <--- 4. failed and return error > >> sb->s_root = NULL; > >> deactivate_locked_super() > >> kill_block_super() > >> generic_shutdown_super() > >> <--- 5. did not evict_inodes > >> put_super() > >> __put_super() > >> <--- 6. put super block > >> > >> Because of the truncated inodes was dirty and will write them back later, it > >> will trigger use after free problem. Now the question is why we need to set > >> SB_ACTIVE bit when enable CONFIG_QUOTA below? > >> > >> #ifdef CONFIG_QUOTA > >> /* Needed for iput() to work correctly and not trash data */ > >> sb->s_flags |= SB_ACTIVE; > >> > >> This code was merged long long ago in v2.6.6, IIUC, it may not affect > >> the quota statistics it we evict inode directly in the last iput. > >> In order to slove this UAF problem, I'm not sure is there any side effect > >> if we just remove this code, or remove SB_ACTIVE and call evict_inodes() > >> in the error path of ext4_fill_super(). > >> > >> Could you give some suggestions? > > > > That's a very good question. I do remember that I've added this code back > > then because otherwise orphan cleanup was loosing updates to quota files. > > But you're right that now I don't see how that could be happening and it > > would be nice if we could get rid of this hack (and even better if it also > > fixes the problem you've found). I guess I'll just try and test this change > > with various quota configurations to see whether something still breaks or > > not. Thanks report! > > > > Thanks for taking time to look at this, is this change OK under your various > quota test cases? Yes, I did tests both with journalled quotas and with ext4 quota feature and the quota accounting was correct after orphan recovery. So just removing the SB_ACTIVE setting is fine AFAICT. Will you send a patch or should I do it? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
