Re: [PATCH] btrfs: add a sanity check for csum root before fill the data csum

[David Sterba <dsterba@suse.cz>]

On Wed, Oct 23, 2024 at 07:04:40PM +0800, Edward Adam Davis wrote:
> Syzbot reported a null-ptr-deref in btrfs_lookup_csums_bitmap.
> The btrfs info contains IGNOREDATACSUMS, which prevents the csum root from
> being loaded.
> Before filling in the csum data, check the flag BTRFS_FS_STATE_NO_DATA_CSUMS
> to confirm that the csum root has been loaded.
> 
> Reported-and-tested-by: syzbot+5d2b33d7835870519b5f@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5d2b33d7835870519b5f
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>

Added to for-next, thanks.

> ---
>  fs/btrfs/scrub.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 3a3427428074..1ba4d8ba902b 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -1602,7 +1602,8 @@ static int scrub_find_fill_first_stripe(struct btrfs_block_group *bg,
>  	}
>  
>  	/* Now fill the data csum. */
> -	if (bg->flags & BTRFS_BLOCK_GROUP_DATA) {
> +	if (!test_bit(BTRFS_FS_STATE_NO_DATA_CSUMS, &fs_info->fs_state) &&

I've updatd the coment as this is double negation that could be
confusing on a quick read.

> +	    bg->flags & BTRFS_BLOCK_GROUP_DATA) {
>  		int sector_nr;
>  		unsigned long csum_bitmap = 0;
>  
> -- 
> 2.43.0
>