Subject: Re: [PATCH bpf-next 4/8] bpf: Teach verifier that certain helpers accept NULL pointer.

From: David Vernet <[email-masked]>
Date: Tue, 4 Apr 2023 09:46:52 -0500

On Mon, Apr 03, 2023 at 09:50:25PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <[email-masked]>
> 
> bpf_[sk|inode|task|cgrp]_storage_[get|delete]() and bpf_get_socket_cookie() helpers
> perform run-time check that sk|inode|task|cgrp pointer != NULL.
> Teach verifier about this fact and allow bpf programs to pass
> PTR_TO_BTF_ID | PTR_MAYBE_NULL into such helpers.
> It will be used in the subsequent patch that will do
> bpf_sk_storage_get(.., skb->sk, ...);
> Even when 'skb' pointer is trusted the 'sk' pointer may be NULL.
> 
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> ---
>  kernel/bpf/bpf_cgrp_storage.c  | 4 ++--
>  kernel/bpf/bpf_inode_storage.c | 4 ++--
>  kernel/bpf/bpf_task_storage.c  | 8 ++++----
>  net/core/bpf_sk_storage.c      | 4 ++--
>  net/core/filter.c              | 2 +-
>  5 files changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/bpf/bpf_cgrp_storage.c b/kernel/bpf/bpf_cgrp_storage.c
> index d17d5b694668..d44fe8dd9732 100644
> --- a/kernel/bpf/bpf_cgrp_storage.c
> +++ b/kernel/bpf/bpf_cgrp_storage.c
> @@ -224,7 +224,7 @@ const struct bpf_func_proto bpf_cgrp_storage_get_proto = {
>  	.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,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &bpf_cgroup_btf_id[0],
>  	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
>  	.arg4_type	= ARG_ANYTHING,
> @@ -235,6 +235,6 @@ const struct bpf_func_proto bpf_cgrp_storage_delete_proto = {
>  	.gpl_only	= false,
>  	.ret_type	= RET_INTEGER,
>  	.arg1_type	= ARG_CONST_MAP_PTR,
> -	.arg2_type	= ARG_PTR_TO_BTF_ID,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &bpf_cgroup_btf_id[0],
>  };
> diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
> index e17ad581b9be..a4d93df78c75 100644
> --- a/kernel/bpf/bpf_inode_storage.c
> +++ b/kernel/bpf/bpf_inode_storage.c
> @@ -229,7 +229,7 @@ const struct bpf_func_proto bpf_inode_storage_get_proto = {
>  	.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,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &bpf_inode_storage_btf_ids[0],
>  	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
>  	.arg4_type	= ARG_ANYTHING,
> @@ -240,6 +240,6 @@ const struct bpf_func_proto bpf_inode_storage_delete_proto = {
>  	.gpl_only	= false,
>  	.ret_type	= RET_INTEGER,
>  	.arg1_type	= ARG_CONST_MAP_PTR,
> -	.arg2_type	= ARG_PTR_TO_BTF_ID,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &bpf_inode_storage_btf_ids[0],
>  };
> diff --git a/kernel/bpf/bpf_task_storage.c b/kernel/bpf/bpf_task_storage.c
> index d1af0c8f9ce4..adf6dfe0ba68 100644
> --- a/kernel/bpf/bpf_task_storage.c
> +++ b/kernel/bpf/bpf_task_storage.c
> @@ -338,7 +338,7 @@ const struct bpf_func_proto bpf_task_storage_get_recur_proto = {
>  	.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,
> +	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
>  	.arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
>  	.arg4_type = ARG_ANYTHING,
> @@ -349,7 +349,7 @@ const struct bpf_func_proto bpf_task_storage_get_proto = {
>  	.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,
> +	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
>  	.arg3_type = ARG_PTR_TO_MAP_VALUE_OR_NULL,
>  	.arg4_type = ARG_ANYTHING,
> @@ -360,7 +360,7 @@ const struct bpf_func_proto bpf_task_storage_delete_recur_proto = {
>  	.gpl_only = false,
>  	.ret_type = RET_INTEGER,
>  	.arg1_type = ARG_CONST_MAP_PTR,
> -	.arg2_type = ARG_PTR_TO_BTF_ID,
> +	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
>  };
>  
> @@ -369,6 +369,6 @@ const struct bpf_func_proto bpf_task_storage_delete_proto = {
>  	.gpl_only = false,
>  	.ret_type = RET_INTEGER,
>  	.arg1_type = ARG_CONST_MAP_PTR,
> -	.arg2_type = ARG_PTR_TO_BTF_ID,
> +	.arg2_type = ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id = &btf_tracing_ids[BTF_TRACING_TYPE_TASK],
>  };
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> index 085025c7130a..d4172534dfa8 100644
> --- a/net/core/bpf_sk_storage.c
> +++ b/net/core/bpf_sk_storage.c
> @@ -412,7 +412,7 @@ const struct bpf_func_proto bpf_sk_storage_get_tracing_proto = {
>  	.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,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
>  	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
>  	.arg4_type	= ARG_ANYTHING,
> @@ -424,7 +424,7 @@ const struct bpf_func_proto bpf_sk_storage_delete_tracing_proto = {
>  	.gpl_only	= false,
>  	.ret_type	= RET_INTEGER,
>  	.arg1_type	= ARG_CONST_MAP_PTR,
> -	.arg2_type	= ARG_PTR_TO_BTF_ID,
> +	.arg2_type	= ARG_PTR_TO_BTF_ID_OR_NULL,
>  	.arg2_btf_id	= &btf_sock_ids[BTF_SOCK_TYPE_SOCK_COMMON],
>  	.allowed	= bpf_sk_storage_tracing_allowed,
>  };

Should we also add PTR_MAYBE_NULL to the ARG_PTR_TO_BTF_ID_SOCK_COMMON
arg in bpf_sk_storage_get_proto and bpf_sk_storage_delete_proto?

> diff --git a/net/core/filter.c b/net/core/filter.c
> index 1f2abf0f60e6..727c5269867d 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4998,7 +4998,7 @@ const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto = {
>  	.func		= bpf_get_socket_ptr_cookie,
>  	.gpl_only	= false,
>  	.ret_type	= RET_INTEGER,
> -	.arg1_type	= ARG_PTR_TO_BTF_ID_SOCK_COMMON,
> +	.arg1_type	= ARG_PTR_TO_BTF_ID_SOCK_COMMON | PTR_MAYBE_NULL,
>  };
>  
>  BPF_CALL_1(bpf_get_socket_cookie_sock_ops, struct bpf_sock_ops_kern *, ctx)
> -- 
> 2.34.1
>