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

[David Sterba <dsterba@suse.cz>]

On Mon, Jan 17, 2022 at 10:48:29AM +0800, Su Yue wrote:
> 
> 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?

Yes, updated in patch, thanks.