Re: [PATCH] btrfs: tree-checker: add btrfs dev extent checks

[David Sterba <dsterba@suse.cz>]

On Sun, Aug 11, 2024 at 03:20:08PM +0930, Qu Wenruo wrote:
> [REPORT]
> There is a corruption report that btrfs refuse to mount a fs that has
> overlapping dev extents:
> 
>  BTRFS error (device sdc): dev extent devid 4 physical offset
> 14263979671552 overlap with previous dev extent end 14263980982272
>  BTRFS error (device sdc): failed to verify dev extents against chunks: -117
>  BTRFS error (device sdc): open_ctree failed
> 
> [CAUSE]
> The cause is very obvious, there is a bad dev extent item with incorrect
> length.
> Although we are not 100% sure of the cause before getting the dev tree
> dump, I'm already surprised that we do not have any checks on dev tree.
> 
> Currently we only do the dev-extent verification at mount time, but if the
> corruption is caused by memory bitflip, we really want to catch it before
> writing the corruption to the storage.
> 
> Furthermore the dev extent items has the following key definition:
> 
> 	(<device id> DEV_EXTENT <physical offset>)
> 
> Thus we can not just rely on the generic key order check to make sure
> there is no overlapping.
> 
> [ENHANCEMENT]
> Introduce dedicated dev extent checks, including:
> 
> - Fixed member checks
>   * chunk_tree should always be BTRFS_CHUNK_TREE_OBJECTID (3)
>   * chunk_objectid should always be
>     BTRFS_FIRST_CHUNK_CHUNK_TREE_OBJECTID (256)
> 
> - Alignment checks
>   * chunk_offset should be aligned to sectorsize
>   * length should be aligned to sectorsize
>   * key.offset should be aligned to sectorsize
> 
> - Overlap checks
>   If the previous key is also a dev-extent item, with the same
>   device id, make sure we do not overlap with the previous dev extent.
> 
> Reported: Stefan N <stefannnau@gmail.com>
> Link: https://lore.kernel.org/linux-btrfs/CA+W5K0rSO3koYTo=nzxxTm1-Pdu1HYgVxEpgJ=aGc7d=E8mGEg@mail.gmail.com/
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Looks like we missed some simple tree item checks indeed.

Reviewed-by: David Sterba <dsterba@suse.com>