Re: [PATCH 0/2] btrfs-progs: mkfs: extent-tree-v2 related fixes

[David Sterba <dsterba@suse.cz>]

On Fri, Oct 07, 2022 at 08:02:59PM +0800, Qu Wenruo wrote:
> Although recently we still have some uncertainty around the on-disk
> format for extent-tree-v2, related to how to determine the number
> of global roots, most of the on-disk format is fixed.
> 
> And even with the uncertain part involved, mkfs.btrfs should not crash
> for extent-tree-v2 feature (hidden behind the experimental builds).
> 
> There are two bugs involved:
> 
> - A crash caused by incorrectly set chunk_objectid for block group item
>   As extent-tree-v2 feature reuse that member to indicate which extent
>   tree a block group belongs to.
> 
>   But the regular fs uses a fixed 256 for that chunk_objectid, and no
>   extent-tree-v2 btrfs would have that many global roots.
> 
>   This leads to btrfs_extent_root() to return NULL, and cause later
>   segfault.
> 
>   Fix it by properly setting chunk_objectid.
>   This is a regression caused by 1430b41427b5 ("btrfs-progs: separate
>   block group tree from extent tree v2").
> 
> - A stack-over-flow caused by too long feature string
>   With extent-tree-v2 enabled, we have at least 84 bytes long feature
>   string (unified features, including compat_ro features likle fst).
> 
>   This is beyond the hard-coded 64 bytes limit.
> 
>   Fix it by introducing a new macro to indicate a minimal safe buf size,
>   and a sanity check to make sure that macro is really large enough.
> 
> Qu Wenruo (2):
>   btrfs-progs: mkfs: fix a crash when enabling extent-tree-v2
>   btrfs-progs: mkfs: fix a stack over-flow when features string are too
>     long

Added to devel, thanks.