Re: [PATCH v2 05/17] btrfs: add inode encryption contexts

[Josef Bacik <josef@toxicpanda.com>]

On Sun, Jul 16, 2023 at 11:52:36PM -0400, Sweet Tea Dorminy wrote:
> From: Omar Sandoval <osandov@osandov.com>
> 
> In order to store encryption information for directories, symlinks,
> etc., fscrypt stores a context item with each encrypted non-regular
> inode. fscrypt provides an arbitrary blob for the filesystem to store,
> and it does not clearly fit into an existing structure, so this goes in
> a new item type.
> 
> Signed-off-by: Omar Sandoval <osandov@osandov.com>
> Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
> ---
>  fs/btrfs/fscrypt.c              | 118 ++++++++++++++++++++++++++++++++
>  fs/btrfs/fscrypt.h              |   2 +
>  fs/btrfs/inode.c                |  19 +++++
>  fs/btrfs/ioctl.c                |   8 ++-
>  include/uapi/linux/btrfs_tree.h |  10 +++
>  5 files changed, 155 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/fscrypt.c b/fs/btrfs/fscrypt.c
> index 3a53dc59c1e4..1dfddf827cf8 100644
> --- a/fs/btrfs/fscrypt.c
> +++ b/fs/btrfs/fscrypt.c
> @@ -1,8 +1,126 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +#include <linux/iversion.h>
>  #include "ctree.h"
> +#include "accessors.h"
> +#include "btrfs_inode.h"
> +#include "disk-io.h"
> +#include "fs.h"
>  #include "fscrypt.h"
> +#include "ioctl.h"
> +#include "messages.h"
> +#include "transaction.h"
> +#include "xattr.h"
> +
> +static int btrfs_fscrypt_get_context(struct inode *inode, void *ctx, size_t len)
> +{
> +	struct btrfs_key key = {
> +		.objectid = btrfs_ino(BTRFS_I(inode)),
> +		.type = BTRFS_FSCRYPT_CTX_ITEM_KEY,
> +		.offset = 0,
> +	};
> +	struct btrfs_path *path;
> +	struct extent_buffer *leaf;
> +	unsigned long ptr;
> +	int ret;
> +
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +
> +	ret = btrfs_search_slot(NULL, BTRFS_I(inode)->root, &key, path, 0, 0);
> +	if (ret) {
> +		len = -ENOENT;
> +		goto out;
> +	}
> +
> +	leaf = path->nodes[0];
> +	ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
> +	/* fscrypt provides max context length, but it could be less */
> +	len = min_t(size_t, len, btrfs_item_size(leaf, path->slots[0]));
> +	read_extent_buffer(leaf, ctx, ptr, len);
> +
> +out:
> +	btrfs_free_path(path);
> +	return len;
> +}
> +
> +static void btrfs_fscrypt_update_context(struct btrfs_path *path,
> +					 const void *ctx, size_t len)
> +{
> +	struct extent_buffer *leaf = path->nodes[0];
> +	unsigned long ptr = btrfs_item_ptr_offset(leaf, path->slots[0]);
> +
> +	len = min_t(size_t, len, btrfs_item_size(leaf, path->slots[0]));
> +	write_extent_buffer(leaf, ctx, ptr, len);
> +	btrfs_mark_buffer_dirty(leaf);
> +}
> +
> +static int btrfs_fscrypt_set_context(struct inode *inode, const void *ctx,
> +				     size_t len, void *fs_data)
> +{
> +	struct btrfs_path *path;
> +	int ret;
> +	struct btrfs_trans_handle *trans = fs_data;
> +	struct btrfs_key key = {
> +		.objectid = btrfs_ino(BTRFS_I(inode)),
> +		.type = BTRFS_FSCRYPT_CTX_ITEM_KEY,
> +		.offset = 0,
> +	};
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +

Reorder the declarations above to make it cleaner, add a newline between the
variables and allocating path.

> +	if (!trans)
> +		trans = btrfs_start_transaction(BTRFS_I(inode)->root, 1);
> +	if (IS_ERR(trans))
> +		return PTR_ERR(trans);
> +
> +	ret = btrfs_search_slot(trans, BTRFS_I(inode)->root, &key, path, 0, 1);
> +	if (ret == 0) {
> +		btrfs_fscrypt_update_context(path, ctx, len);
> +		btrfs_free_path(path);

What do we do with the transaction if we started it above?  Are we responsible
for stopping the transaction if it was provided via fsdata?

> +		return ret;
> +	}
> +
> +	btrfs_free_path(path);
> +	if (ret < 0) {
> +		btrfs_abort_transaction(trans, ret);
> +		return ret;
> +	}
> +
> +	ret = btrfs_insert_item(trans, BTRFS_I(inode)->root, &key, (void *) ctx, len);

We already have the path here, we can do

btrfs_release_path(path);
ret = btrfs_insert_empty_item(trans, BTRFS_I(inode)->root, &key, len);
if (ret) {
	btrfs_abort_transaction(trans, ret);
	btrfs_end_transaction(trans);
	return ret;
}

ptr = btrfs_item_ptr_offset(path->nodes[0], path->slots[0]);
write_extent_buffer(path->nodes[0], ctx, ptr, len);
btrfs_mark_buffer_dirty(path->nodes[0]);
btrfs_free_path(path);

> +	if (ret) {
> +		btrfs_abort_transaction(trans, ret);
> +		return ret;
> +	}
> +
> +	if (fs_data)
> +		return ret;
> +
> +	BTRFS_I(inode)->flags |= BTRFS_INODE_ENCRYPT;
> +	btrfs_sync_inode_flags_to_i_flags(inode);
> +	inode_inc_iversion(inode);
> +	inode->i_ctime = current_time(inode);
> +	ret = btrfs_update_inode(trans, BTRFS_I(inode)->root, BTRFS_I(inode));
> +	if (!ret) {
> +		btrfs_end_transaction(trans);
> +		return ret;
> +	}
> +
> +	btrfs_abort_transaction(trans, ret);

Still need to call end_transaction if we abort if we started it.  Thanks,

Josef