Re: [PATCH bpf-next v4 2/4] bpf: Implement bpf_local_storage for inodes

[Martin KaFai Lau]

On Thu, Jul 09, 2020 at 12:12:37PM +0200, KP Singh wrote:
> From: KP Singh <kpsingh@xxxxxxxxxx>
> 
> Similar to bpf_local_storage for sockets, add local storage for inodes.
> The life-cycle of storage is managed with the life-cycle of the inode.
> i.e. the storage is destroyed along with the owning inode.
> 
> The BPF LSM allocates an __rcu pointer to the bpf_local_storage in the
> security blob which are now stackable and can co-exist with other LSMs.
> 
> Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>

[ ... ]


> +static void *bpf_inode_storage_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	struct bpf_local_storage_data *sdata;
> +	struct inode *inode;
> +	int err = -EINVAL;
> +
> +	if (key) {
> +		inode = *(struct inode **)(key);
The bpf_inode_storage_lookup_elem() here and the (update|delete)_elem() below
are called from the userspace syscall.  How the userspace may provide this key?

> +		sdata = inode_storage_lookup(inode, map, true);
> +		return sdata ? sdata->data : NULL;
> +	}
> +
> +	return ERR_PTR(err);
> +}
> +
> +static int bpf_inode_storage_update_elem(struct bpf_map *map, void *key,
> +					 void *value, u64 map_flags)
> +{
> +	struct bpf_local_storage_data *sdata;
> +	struct inode *inode;
> +	int err = -EINVAL;
> +
> +	if (key) {
> +		inode = *(struct inode **)(key);
> +		sdata = map->ops->map_local_storage_update(inode, map, value,
> +							   map_flags);
> +		return PTR_ERR_OR_ZERO(sdata);
> +	}
> +	return err;
> +}
> +
> +static int inode_storage_delete(struct inode *inode, struct bpf_map *map)
> +{
> +	struct bpf_local_storage_data *sdata;
> +
> +	sdata = inode_storage_lookup(inode, map, false);
> +	if (!sdata)
> +		return -ENOENT;
> +
> +	bpf_selem_unlink_map_elem(SELEM(sdata));
> +
> +	return 0;
> +}
> +
> +static int bpf_inode_storage_delete_elem(struct bpf_map *map, void *key)
> +{
> +	struct inode *inode;
> +	int err = -EINVAL;
> +
> +	if (key) {
> +		inode = *(struct inode **)(key);
> +		err = inode_storage_delete(inode, map);
> +	}
> +
> +	return err;
> +}
> +

[ ... ]

> +static int inode_storage_map_btf_id;
> +const struct bpf_map_ops inode_storage_map_ops = {
> +	.map_alloc_check = bpf_local_storage_map_alloc_check,
> +	.map_alloc = inode_storage_map_alloc,
> +	.map_free = inode_storage_map_free,
> +	.map_get_next_key = notsupp_get_next_key,
> +	.map_lookup_elem = bpf_inode_storage_lookup_elem,
> +	.map_update_elem = bpf_inode_storage_update_elem,
> +	.map_delete_elem = bpf_inode_storage_delete_elem,
> +	.map_check_btf = bpf_local_storage_map_check_btf,
> +	.map_btf_name = "bpf_local_storage_map",
> +	.map_btf_id = &inode_storage_map_btf_id,
> +	.map_local_storage_alloc = inode_storage_alloc,
> +	.map_selem_alloc = inode_selem_alloc,
> +	.map_local_storage_update = inode_storage_update,
> +	.map_local_storage_unlink = unlink_inode_storage,
> +};
> +