On Mon, 17 May 2021 12:15:23 +0200
Jan Kara <jack@xxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
>
> 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
