linux-kernel - Re: [PATCH] jfs: fix log->bdev_handle null ptr deref in lbmStartIO

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Date:   Mon, 9 Oct 2023 12:08:25 +0200
From:   Jan Kara <jack@...e.cz>
To:     Lizhi Xu <lizhi.xu@...driver.com>
Cc:     syzbot+23bc20037854bb335d59@...kaller.appspotmail.com,
        axboe@...nel.dk, brauner@...nel.org, dave.kleikamp@...cle.com,
        hare@...e.de, hch@....de, jack@...e.cz,
        jfs-discussion@...ts.sourceforge.net, johannes.thumshirn@....com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        shaggy@...nel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] jfs: fix log->bdev_handle null ptr deref in lbmStartIO

On Mon 09-10-23 17:45:57, Lizhi Xu wrote:
> When sbi->flag is JFS_NOINTEGRITY in lmLogOpen(), log->bdev_handle can't
> be inited, so it value will be NULL.
> Therefore, add the "log ->no_integrity=1" judgment in lbmStartIO() to avoid such
> problems.
> 
> Reported-and-tested-by: syzbot+23bc20037854bb335d59@...kaller.appspotmail.com
> Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>

Ah, good catch. Who would think someone creates bios for NULL bdev only to
release them shortly afterwards ;). Anyway the fix looks good. Feel free to
add:

Reviewed-by: Jan Kara <jack@...e.cz>

Christian, please pick up this fixup into your tree. Thanks!

								Honza

> ---
>  fs/jfs/jfs_logmgr.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
> index c911d838b8ec..c41a76164f84 100644
> --- a/fs/jfs/jfs_logmgr.c
> +++ b/fs/jfs/jfs_logmgr.c
> @@ -2110,10 +2110,14 @@ static void lbmStartIO(struct lbuf * bp)
>  {
>  	struct bio *bio;
>  	struct jfs_log *log = bp->l_log;
> +	struct block_device *bdev = NULL;
>  
>  	jfs_info("lbmStartIO");
>  
> -	bio = bio_alloc(log->bdev_handle->bdev, 1, REQ_OP_WRITE | REQ_SYNC,
> +	if (!log->no_integrity) 
> +		bdev = log->bdev_handle->bdev;	
> +
> +	bio = bio_alloc(bdev, 1, REQ_OP_WRITE | REQ_SYNC,
>  			GFP_NOFS);
>  	bio->bi_iter.bi_sector = bp->l_blkno << (log->l2bsize - 9);
>  	__bio_add_page(bio, bp->l_page, LOGPSIZE, bp->l_offset);
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR