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Date:   Mon, 17 May 2021 15:08:18 +0200
From:   Jan Kara <jack@suse.cz>
To:     Pavel Skripkin <paskripkin@gmail.com>
Cc:     jack@suse.cz, tiantao6@hisilicon.com, rdunlap@infradead.org,
        reiserfs-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
Subject: Re: [PATCH v2] reiserfs: add check for invalid 1st journal block
Message-ID: <20210517130818.GB25760@quack2.suse.cz>
References: <20210517101523.GB31755@quack2.suse.cz>
 <20210517121545.29645-1-paskripkin@gmail.com>
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On Mon 17-05-21 15:15:45, 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-by: syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>

Thanks! I've added the patch to my tree.

								Honza

> ---
> 
> Changes in v2:
>   Added necessary !SB_ONDISK_JOURNAL_DEVICE(sb) in "if"
> 
> ---
>  fs/reiserfs/journal.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
> index 9edc8e2b154e..0834b101c316 100644
> --- a/fs/reiserfs/journal.c
> +++ b/fs/reiserfs/journal.c
> @@ -2758,6 +2758,20 @@ int journal_init(struct super_block *sb, const char *j_dev_name,
>  		goto free_and_return;
>  	}
>  
> +	/*
> +	 * Sanity check to see if journal first block is correct.
> +	 * If journal first block is invalid it can cause
> +	 * zeroing important superblock members.
> +	 */
> +	if (!SB_ONDISK_JOURNAL_DEVICE(sb) &&
> +	    SB_ONDISK_JOURNAL_1st_BLOCK(sb) < SB_JOURNAL_1st_RESERVED_BLOCK(sb)) {
> +		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
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR