Re: [PATCH bpf-next 2/4] bpf: Make bpf inode storage available to tracing program

[Christian Brauner <brauner@kernel.org>]

On Tue, Nov 12, 2024 at 12:25:56AM -0800, Song Liu wrote:
> inode storage can be useful for non-LSM program. For example, file* tools
> from bcc/libbpf-tools can use inode storage instead of hash map; fanotify
> fastpath [1] can also use inode storage to store useful data.
> 
> Make inode storage available for tracing program. Move bpf inode storage
> from a security blob to inode->i_bpf_storage, and adjust related code
> accordingly.
> 
> [1] https://lore.kernel.org/linux-fsdevel/20241029231244.2834368-1-song@kernel.org/
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  fs/inode.c                     |  1 +
>  include/linux/bpf.h            |  9 +++++++++
>  include/linux/bpf_lsm.h        | 29 -----------------------------
>  include/linux/fs.h             |  4 ++++
>  kernel/bpf/Makefile            |  3 +--
>  kernel/bpf/bpf_inode_storage.c | 32 +++++---------------------------
>  kernel/bpf/bpf_lsm.c           |  4 ----
>  kernel/trace/bpf_trace.c       |  4 ++++
>  security/bpf/hooks.c           |  6 ------
>  9 files changed, 24 insertions(+), 68 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 8dabb224f941..3c679578169f 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -286,6 +286,7 @@ static struct inode *alloc_inode(struct super_block *sb)
>  void __destroy_inode(struct inode *inode)
>  {
>  	BUG_ON(inode_has_buffers(inode));
> +	bpf_inode_storage_free(inode);
>  	inode_detach_wb(inode);
>  	security_inode_free(inode);
>  	fsnotify_inode_delete(inode);
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 1b84613b10ac..0b31d2e74df6 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2672,6 +2672,7 @@ struct bpf_link *bpf_link_by_id(u32 id);
>  const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id,
>  						 const struct bpf_prog *prog);
>  void bpf_task_storage_free(struct task_struct *task);
> +void bpf_inode_storage_free(struct inode *inode);
>  void bpf_cgrp_storage_free(struct cgroup *cgroup);
>  bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
>  const struct btf_func_model *
> @@ -2942,6 +2943,10 @@ static inline void bpf_task_storage_free(struct task_struct *task)
>  {
>  }
>  
> +static inline void bpf_inode_storage_free(struct inode *inode)
> +{
> +}
> +
>  static inline bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
>  {
>  	return false;
> @@ -3305,6 +3310,10 @@ extern const struct bpf_func_proto bpf_task_storage_get_recur_proto;
>  extern const struct bpf_func_proto bpf_task_storage_get_proto;
>  extern const struct bpf_func_proto bpf_task_storage_delete_recur_proto;
>  extern const struct bpf_func_proto bpf_task_storage_delete_proto;
> +extern const struct bpf_func_proto bpf_inode_storage_get_proto;
> +extern const struct bpf_func_proto bpf_inode_storage_get_recur_proto;
> +extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
> +extern const struct bpf_func_proto bpf_inode_storage_delete_recur_proto;
>  extern const struct bpf_func_proto bpf_for_each_map_elem_proto;
>  extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;
>  extern const struct bpf_func_proto bpf_sk_setsockopt_proto;
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index aefcd6564251..a819c2f0a062 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -19,31 +19,12 @@
>  #include <linux/lsm_hook_defs.h>
>  #undef LSM_HOOK
>  
> -struct bpf_storage_blob {
> -	struct bpf_local_storage __rcu *storage;
> -};
> -
> -extern struct lsm_blob_sizes bpf_lsm_blob_sizes;
> -
>  int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>  			const struct bpf_prog *prog);
>  
>  bool bpf_lsm_is_sleepable_hook(u32 btf_id);
>  bool bpf_lsm_is_trusted(const struct bpf_prog *prog);
>  
> -static inline struct bpf_storage_blob *bpf_inode(
> -	const struct inode *inode)
> -{
> -	if (unlikely(!inode->i_security))
> -		return NULL;
> -
> -	return inode->i_security + bpf_lsm_blob_sizes.lbs_inode;
> -}
> -
> -extern const struct bpf_func_proto bpf_inode_storage_get_proto;
> -extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
> -void bpf_inode_storage_free(struct inode *inode);
> -
>  void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func);
>  
>  int bpf_lsm_get_retval_range(const struct bpf_prog *prog,
> @@ -66,16 +47,6 @@ static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>  	return -EOPNOTSUPP;
>  }
>  
> -static inline struct bpf_storage_blob *bpf_inode(
> -	const struct inode *inode)
> -{
> -	return NULL;
> -}
> -
> -static inline void bpf_inode_storage_free(struct inode *inode)
> -{
> -}
> -
>  static inline void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog,
>  					   bpf_func_t *bpf_func)
>  {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 3559446279c1..479097e4dd5b 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -79,6 +79,7 @@ struct fs_context;
>  struct fs_parameter_spec;
>  struct fileattr;
>  struct iomap_ops;
> +struct bpf_local_storage;
>  
>  extern void __init inode_init(void);
>  extern void __init inode_init_early(void);
> @@ -648,6 +649,9 @@ struct inode {
>  #ifdef CONFIG_SECURITY
>  	void			*i_security;
>  #endif
> +#ifdef CONFIG_BPF_SYSCALL
> +	struct bpf_local_storage __rcu *i_bpf_storage;
> +#endif

Sorry, we're not growing struct inode for this. It just keeps getting
bigger. Last cycle we freed up 8 bytes to shrink it and we're not going
to waste them on special-purpose stuff. We already NAKed someone else's
pet field here.