bpf: Allow BTF ctx access for string pointers (84ad7a7a) · Commits · 戴 / test

When accessing the context we allow access to arguments with scalar type and pointer to struct. But we deny access for pointer to scalar type, which is the case for many functions. Alexei suggested to take conservative approach and allow currently only string pointer access, which is the case for most functions now: Adding check if the pointer is to string type and allow access to it. Suggested-by:

Alexei Starovoitov <ast@kernel.org> Signed-off-by:

Jiri Olsa <jolsa@kernel.org> Signed-off-by:

Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200123161508.915203-2-jolsa@kernel.org

kernel/bpf/btf.c

+16 −0

Original line number	Diff line number	Diff line
		@@ -3669,6 +3669,19 @@ struct btf bpf_prog_get_target_btf(const struct bpf_prog prog)
		}
		}

		static bool is_string_ptr(struct btf btf, const struct btf_type t)
		{
		/* t comes in already as a pointer */
		t = btf_type_by_id(btf, t->type);

		/* allow const */
		if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
		t = btf_type_by_id(btf, t->type);

		/* char, signed char, unsigned char */
		return btf_type_is_int(t) && t->size == 1;
		}

		bool btf_ctx_access(int off, int size, enum bpf_access_type type,
		const struct bpf_prog *prog,
		struct bpf_insn_access_aux *info)
		@@ -3735,6 +3748,9 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
		*/
		return true;

		if (is_string_ptr(btf, t))
		return true;

		/* this is a pointer to another type */
		info->reg_type = PTR_TO_BTF_ID;

Admin message