Re: [PATCH] btrfs: validate ROOT_BACKREF name before copying subvolume info

[Zhang Cen <rollkingzzc@gmail.com>]

On Sun, May 10, 2026 at 04:18:00PM +0800, Qu Wenruo wrote:
> The validation is too late.
> 
> btrfs subvolume creation only accept BTRFS_SUBVOL_NAME_MAX + 1 (for the
> terminating \0).
> 
> This means a subvolume ref/backref should not have a name longer than
> BTRFS_SUBVOL_NAME_MAX in the first place.
> 
> Such independent checks should all be done inside tree-checker.

Agreed, thanks for the review.

I'll move the on-disk ROOT_REF/ROOT_BACKREF validation into tree-checker
for v2 and cover both key types there. The v2 change will reject items
smaller than struct btrfs_root_ref, reject records where name_len does not
match the item payload, and reject names longer than BTRFS_SUBVOL_NAME_MAX.

I'll keep the BTRFS_IOC_GET_SUBVOL_INFO-side BTRFS_VOL_NAME_MAX check only
as the local guard for its fixed-size UAPI output buffer before copying the
already validated name.

Thanks,
Zhang