Re: [PATCH 1/2] quota: fix null-ptr-deref in ext4_acquire_dquot()

[yebin (H)]

On 2023/6/5 19:51, Jan Kara wrote:
> On Sat 03-06-23 14:14:11, yebin (H) wrote:
> > On 2023/5/30 17:57, Jan Kara wrote:
> > > On Sat 27-05-23 09:40:17, Ye Bin wrote:
> > > > Syzbot found the following issue:
> > > > Unable to handle kernel paging request at virtual address dfff800000000005
> > > > KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> > > ...
> > > > CPU: 0 PID: 6080 Comm: syz-executor747 Not tainted 6.3.0-rc7-syzkaller-g14f8db1c0f9a #0
> > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
> > > > pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > > > pc : ext4_acquire_dquot+0x1d4/0x398 fs/ext4/super.c:6766
> > > > lr : dquot_to_inode fs/ext4/super.c:6740 [inline]
> > > > lr : ext4_acquire_dquot+0x1ac/0x398 fs/ext4/super.c:6766
> > > OK, this is bad...
> > >
> > > > Above issue may happens as follows:
> > > > ProcessA              ProcessB                    ProcessC
> > > > sys_fsconfig
> > > >     vfs_fsconfig_locked
> > > >      reconfigure_super
> > > >        ext4_remount
> > > >         dquot_suspend -> suspend all type quota
> > > >
> > > >                    sys_fsconfig
> > > > 		  vfs_fsconfig_locked
> > > > 		    reconfigure_super
> > > > 		     ext4_remount
> > > > 		      dquot_resume
> > > > 		       ret = dquot_load_quota_sb
> > > >                           add_dquot_ref
> > > > 		                           do_open  -> open file O_RDWR
> > > > 					    vfs_open
> > > > 					     do_dentry_open
> > > > 					      get_write_access
> > > > 					       atomic_inc_unless_negative(&inode->i_writecount)
> > > >                                                 ext4_file_open
> > > > 					       dquot_file_open
> > > > 					        dquot_initialize
> > > > 						  __dquot_initialize
> > > > 						   dqget
> > > > 						    if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
> > > >
> > > > 			  __dquot_initialize
> > > > 			   __dquot_initialize
> > > > 			    dqget
> > > > 			     if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags))
> > > > 	                       ext4_acquire_dquot -> Return error
> > > > 		       if (ret < 0)
> > > > 	                 vfs_cleanup_quota_inode
> > > > 			  dqopt->files[type] = NULL;
> > > But I don't see how this can happen. The code in dquot_load_quota_sb()
> > > looks like:
> > >
> > >           error = add_dquot_ref(sb, type);
> > >           if (error)
> > >                   dquot_disable(sb, type, flags);
> > >
> > > So if an error happens in add_dquot_ref(), we'll call dquot_disable().
> > > dquot_disable() then does:
> > >
> > >                   drop_dquot_ref(sb, cnt);
> > >                   invalidate_dquots(sb, cnt);
> > >
> > > and invalidate_dquots() waits for reference count of all dquots to drop to
> > > 0. Hence if dqget() returned a dquot pointer to ProcessC, then ProcessB
> > > should wait until ProcessC drops the dquot reference (hence
> > > ext4_acquire_dquot() is done).
> > >
> > > What am I missing?
> > >
> > > 								Honza
> > My reproduction condition is:
> > mkfs.ext4 -F /dev/sda
> > tune2fs  -Q usrquota /dev/sda
> >
> > dquot_disable
> > ...
> >           if ((flags & DQUOT_USAGE_ENABLED && !(flags &
> > DQUOT_LIMITS_ENABLED))
> >               || (flags & DQUOT_SUSPENDED && flags & (DQUOT_LIMITS_ENABLED |
> >               DQUOT_USAGE_ENABLED)))
> >                   return -EINVAL;
> > ...
> > If without enable DQUOT_LIMITS_ENABLED dquot_disable() will just return
> > -EINVAL.
> Aha, that is the bug! Does attached patch fix your problem?
>
> 								Honza
Yes , it's works.