Re: [PATCH 2/3] btrfs: check/original: reject bad metadata backref with invalid level

[Su Yue <l@damenly.su>]

On Mon 17 Jan 2022 at 10:38, Qu Wenruo <wqu@suse.com> wrote:

> [BUG]
> There is a bug report that kernel tree-checker rejected an 
> invalid
> metadata item:
>
>  corrupt leaf: block=934474399744 slot=68 extent 
>  bytenr=425173254144 len=16384 invalid tree level, have 33554432 
>  expect [0, 7]
>
> But original mode btrfs-check reports nothing wrong.
> (BTW, lowmem mode will just crash, and fixed in previous patch).
>
> [CAUSE]
> For original mode it doesn't really check tree level, thus 
> didn't find
> the problem.
>
> [FIX]
> I don't have a good idea to completely make original mode to 
> verify the
> level in backref and in the tree block (while lowmem does that).
>
> But at least we can detect obviouly corrupted level just like 
> kernel.
>
> Now original mode will detect such problem:
>
>  ...
>  [2/7] checking extents
>  ERROR: tree block 30457856 has bad backref level, has 256 
>  expect [0, 7]
>  ref mismatch on [30457856 16384] extent item 0, found 1
>  tree backref 30457856 root 5 not found in extent tree
>  backpointer mismatch on [30457856 16384]
>  ERROR: errors found in extent allocation tree or chunk 
>  allocation
>  [3/7] checking free space tree
>  ...
>
> Reported-by: Stickstoff <stickstoff@posteo.de>
> Link: 
> https://lore.kernel.org/linux-btrfs/6ed4cd5a-7430-f326-4056-25ae7eb44416@posteo.de/
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  check/main.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/check/main.c b/check/main.c
> index 540130b8e223..2dea2acf5104 100644
> --- a/check/main.c
> +++ b/check/main.c
> @@ -5447,6 +5447,25 @@ static int process_extent_item(struct 
> btrfs_root *root,
>  	if (metadata)
>  		btrfs_check_subpage_eb_alignment(gfs_info, 
>  key.objectid, num_bytes);
>
> +	ptr = (unsigned long)(ei + 1);
> +	if (metadata) {
> +		u64 level;
> +
> +		if (key.type == BTRFS_EXTENT_ITEM_KEY) {
> +			struct btrfs_tree_block_info *info;
> +
> +			info = (struct btrfs_tree_block_info 
> *)ptr;
> +			level = btrfs_tree_block_level(eb, info);
> +		} else {
> +			level = key.offset;
> +		}
> +		if (level >= BTRFS_MAX_LEVEL) {
> +			error(
> +	"tree block %llu has bad backref level, has %llu expect 
> [0, %u]",
> +			      key.objectid, level, BTRFS_MAX_LEVEL 
> - 1);
> +			return -EIO;
>
-EUCLEAN is better?

Reviewed-by: Su Yue <l@damenly.su>
--
Su
> +		}
> +	}
>  	memset(&tmpl, 0, sizeof(tmpl));
>  	tmpl.start = key.objectid;
>  	tmpl.nr = num_bytes;