Re: [PATCH] reiserfs: add check for invalid 1st journal block

[Pavel Skripkin <paskripkin@gmail.com>]

On Mon, 17 May 2021 12:15:23 +0200
Jan Kara <jack@suse.cz> wrote:
> On Sat 15-05-21 00:23:35, Pavel Skripkin wrote:
> > syzbot reported divide error in reiserfs.
> > The problem was in incorrect journal 1st block.
> > 
> > Syzbot's reproducer manualy generated wrong superblock
> > with incorrect 1st block. In journal_init() wasn't
> > any checks about this particular case.
> > 
> > For example, if 1st journal block is before superblock
> > 1st block, it can cause zeroing important superblock members
> > in do_journal_end().
> > 
> > Reported-and-tested-by:
> > syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
> 
> Thanks for the patch. One comment below:
> 
> > diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
> > index 9edc8e2b154e..d58f24a08385 100644
> > --- a/fs/reiserfs/journal.c
> > +++ b/fs/reiserfs/journal.c
> > @@ -2758,6 +2758,19 @@ int journal_init(struct super_block *sb,
> > const char *j_dev_name, goto free_and_return;
> >  	}
> >  
> > +	/*
> > +	 * Sanity check to see is journal first block correct.
> > +	 * If journal first block is invalid it can cause
> > +	 * zeroing important superblock members.
> > +	 */
> > +	if (SB_ONDISK_JOURNAL_1st_BLOCK(sb) <
> > SB_JOURNAL_1st_RESERVED_BLOCK(sb)) {
> 
> I guess this check is valid only if !SB_ONDISK_JOURNAL_DEVICE(sb),
> isn't it? Otherwise you are comparing block numbers from two
> different devices...
> 

Hi!

Indeed. Thanks for pointing it out! I'll send v2 soon

> 									Honza
> 
> > +		reiserfs_warning(sb, "journal-1393",
> > +			"journal 1st super block is invalid: 1st
> > reserved block %d, but actual 1st block is %d",
> > +			SB_JOURNAL_1st_RESERVED_BLOCK(sb),
> > +			SB_ONDISK_JOURNAL_1st_BLOCK(sb));
> > +		goto free_and_return;
> > +	}
> > +
> >  	if (journal_init_dev(sb, journal, j_dev_name) != 0) {
> >  		reiserfs_warning(sb, "sh-462",
> >  				 "unable to initialize journal
> > device"); -- 
> > 2.31.1
> > 




With regards,
Pavel Skripkin