Re: [PATCH bpf-next v7 5/7] bpf: Implement bpf_local_storage for inodes

[Martin KaFai Lau <kafai@fb.com>]

On Thu, Jul 30, 2020 at 04:07:14PM +0200, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
> 
> 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.
> 

[ ... ]

> +static int bpf_fd_inode_storage_update_elem(struct bpf_map *map, void *key,
> +					 void *value, u64 map_flags)
> +{
> +	struct bpf_local_storage_data *sdata;
> +	struct file *f;
> +	int fd;
> +
> +	fd = *(int *)key;
> +	f = fcheck(fd);
> +	if (!f)
> +		return -EINVAL;
> +
> +	sdata = bpf_local_storage_update(f->f_inode, map, value, map_flags);
n00b question.  inode will not be going away here (like another
task calls close(fd))?  and there is no chance that bpf_local_storage_update()
will be adding new storage after bpf_inode_storage_free() was called?

A few comments will be useful here.

> +	return PTR_ERR_OR_ZERO(sdata);
> +}
> +
> +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(SELEM(sdata));
> +
> +	return 0;
> +}
> +
> +static int bpf_fd_inode_storage_delete_elem(struct bpf_map *map, void *key)
> +{
> +	struct file *f;
> +	int fd;
> +
> +	fd = *(int *)key;
> +	f = fcheck(fd);
> +	if (!f)
> +		return -EINVAL;
> +
> +	return inode_storage_delete(f->f_inode, map);
> +}
> +
> +BPF_CALL_4(bpf_inode_storage_get, struct bpf_map *, map, struct inode *, inode,
> +	   void *, value, u64, flags)
> +{
> +	struct bpf_local_storage_data *sdata;
> +
> +	if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
> +		return (unsigned long)NULL;
> +
> +	sdata = inode_storage_lookup(inode, map, true);
> +	if (sdata)
> +		return (unsigned long)sdata->data;
> +
> +	if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
> +		sdata = bpf_local_storage_update(inode, map, value,
> +						 BPF_NOEXIST);
The same question here

> +		return IS_ERR(sdata) ? (unsigned long)NULL :
> +					     (unsigned long)sdata->data;
> +	}
> +
> +	return (unsigned long)NULL;
> +}
> +
> +BPF_CALL_2(bpf_inode_storage_delete,
> +	   struct bpf_map *, map, struct inode *, inode)
> +{
> +	return inode_storage_delete(inode, map);
> +}
> +
> +static int notsupp_get_next_key(struct bpf_map *map, void *key,
> +				void *next_key)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static struct bpf_map *inode_storage_map_alloc(union bpf_attr *attr)
> +{
> +	struct bpf_local_storage_map *smap;
> +
> +	smap = bpf_local_storage_map_alloc(attr);
> +	if (IS_ERR(smap))
> +		return ERR_CAST(smap);
> +
> +	smap->cache_idx = bpf_local_storage_cache_idx_get(&inode_cache);
> +	return &smap->map;
> +}
> +
> +static void inode_storage_map_free(struct bpf_map *map)
> +{
> +	struct bpf_local_storage_map *smap;
> +
> +	smap = (struct bpf_local_storage_map *)map;
> +	bpf_local_storage_cache_idx_free(&inode_cache, smap->cache_idx);
> +	bpf_local_storage_map_free(smap);
> +}
> +
> +static int sk_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_fd_inode_storage_lookup_elem,
> +	.map_update_elem = bpf_fd_inode_storage_update_elem,
> +	.map_delete_elem = bpf_fd_inode_storage_delete_elem,
> +	.map_check_btf = bpf_local_storage_map_check_btf,
> +	.map_btf_name = "bpf_local_storage_map",
> +	.map_btf_id = &sk_storage_map_btf_id,
> +	.map_owner_storage_ptr = inode_storage_ptr,
> +};
> +
> +BTF_ID_LIST(bpf_inode_storage_get_btf_ids)
> +BTF_ID(struct, inode)
The ARG_PTR_TO_BTF_ID is the second arg instead of the first
arg in bpf_inode_storage_get_proto.
Does it just happen to work here without needing BTF_ID_UNUSED?

> +
> +const struct bpf_func_proto bpf_inode_storage_get_proto = {
> +	.func		= bpf_inode_storage_get,
> +	.gpl_only	= false,
> +	.ret_type	= RET_PTR_TO_MAP_VALUE_OR_NULL,
> +	.arg1_type	= ARG_CONST_MAP_PTR,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID,
> +	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
> +	.arg4_type	= ARG_ANYTHING,
> +	.btf_id		= bpf_inode_storage_get_btf_ids,
> +};
> +
> +BTF_ID_LIST(bpf_inode_storage_delete_btf_ids)
> +BTF_ID(struct, inode)
> +
> +const struct bpf_func_proto bpf_inode_storage_delete_proto = {
> +	.func		= bpf_inode_storage_delete,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_CONST_MAP_PTR,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID,
> +	.btf_id		= bpf_inode_storage_delete_btf_ids,
> +};