Re: [PATCH] btrfs: fix false alert caused by legacy btrfs root item

[Martin Steigerwald <martin@lichtvoll.de>]

Hi Qu!

Qu Wenruo - 22.09.20, 04:37:01 CEST:
> Commit 259ee7754b67 ("btrfs: tree-checker: Add ROOT_ITEM check")
> introduced btrfs root item size check, however btrfs root item has two
> format, the legacy one which just ends before generation_v2 member,
> is smaller than current btrfs root item size.
>
> This caused btrfs kernel to reject valid but old tree root leaves.
> 
> Fix this problem by also allowing legacy root item, since kernel can
> already handle them pretty well and upgrade to newer root item format
> when needed.

Is this going into 5.9? Asking cause it is not in 5.9-rc8.

Of course I can keep the patch and as the external disk has been fixed, I 
would not even need it anymore.

Best,
Martin

> Reported-by: Martin Steigerwald <martin@lichtvoll.de>
> Fixes: 259ee7754b67 ("btrfs: tree-checker: Add ROOT_ITEM check")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/tree-checker.c         | 17 ++++++++++++-----
>  include/uapi/linux/btrfs_tree.h |  9 +++++++++
>  2 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index 7b1fee630f97..6f794aca48d3 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -1035,7 +1035,7 @@ static int check_root_item(struct extent_buffer
> *leaf, struct btrfs_key *key, int slot)
>  {
>  	struct btrfs_fs_info *fs_info = leaf->fs_info;
> -	struct btrfs_root_item ri;
> +	struct btrfs_root_item ri = { 0 };
>  	const u64 valid_root_flags = BTRFS_ROOT_SUBVOL_RDONLY |
>  				     BTRFS_ROOT_SUBVOL_DEAD;
>  	int ret;
> @@ -1044,14 +1044,21 @@ static int check_root_item(struct
> extent_buffer *leaf, struct btrfs_key *key, if (ret < 0)
>  		return ret;
> 
> -	if (btrfs_item_size_nr(leaf, slot) != sizeof(ri)) {
> +	if (btrfs_item_size_nr(leaf, slot) != sizeof(ri) &&
> +	    btrfs_item_size_nr(leaf, slot) != 
btrfs_legacy_root_item_size())
> { generic_err(leaf, slot,
> -			    "invalid root item size, have %u expect %zu",
> -			    btrfs_item_size_nr(leaf, slot), sizeof(ri));
> +			    "invalid root item size, have %u expect %zu or 
%zu",
> +			    btrfs_item_size_nr(leaf, slot), sizeof(ri),
> +			    btrfs_legacy_root_item_size());
>  	}
> 
> +	/*
> +	 * For legacy root item, the members starting at generation_v2 
will
> be +	 * all filled with 0.
> +	 * And since we allow geneartion_v2 as 0, it will still pass the
> check. +	 */
>  	read_extent_buffer(leaf, &ri, btrfs_item_ptr_offset(leaf, slot),
> -			   sizeof(ri));
> +			   btrfs_item_size_nr(leaf, slot));
> 
>  	/* Generation related */
>  	if (btrfs_root_generation(&ri) >
> diff --git a/include/uapi/linux/btrfs_tree.h
> b/include/uapi/linux/btrfs_tree.h index 9ba64ca6b4ac..464095a28b18
> 100644
> --- a/include/uapi/linux/btrfs_tree.h
> +++ b/include/uapi/linux/btrfs_tree.h
> @@ -644,6 +644,15 @@ struct btrfs_root_item {
>  	__le64 reserved[8]; /* for future */
>  } __attribute__ ((__packed__));
> 
> +/*
> + * Btrfs root item used to be smaller than current size.
> + * The old format ends at where member generation_v2 is.
> + */
> +static inline size_t btrfs_legacy_root_item_size(void)
> +{
> +	return offsetof(struct btrfs_root_item, generation_v2);
> +}
> +
>  /*
>   * this is used for both forward and backward root refs
>   */


-- 
Martin