bpf: Extract program_returns_void() for clarity

From: Eduard Zingerman <eddyz87@gmail.com>

The check_return_code function has explicit checks on whether
a program type can return void. Factor this logic out to reuse
it later for both main progs and subprogs.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Link: https://lore.kernel.org/r/20260228184759.108145-3-emil@etsalapatis.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 89e6d2f6bdf6d1862630cbd16d9fc44ab7d75325..bb9abd42ab125caea5b502cf6af328dfc0ae005b 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17953,6 +17953,28 @@ static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_
        return true;
 }
 
+static bool program_returns_void(struct bpf_verifier_env *env)
+{
+       const struct bpf_prog *prog = env->prog;
+       enum bpf_prog_type prog_type = resolve_prog_type(prog);
+
+       switch (prog_type) {
+       case BPF_PROG_TYPE_LSM:
+               /* See return_retval_range, for BPF_LSM_CGROUP can be 0 or 0-1 depending on hook. */
+               if (prog->expected_attach_type != BPF_LSM_CGROUP &&
+                   !prog->aux->attach_func_proto->type)
+                       return true;
+               break;
+       case BPF_PROG_TYPE_STRUCT_OPS:
+               if (!prog->aux->attach_func_proto->type)
+                       return true;
+               break;
+       default:
+               break;
+       }
+       return false;
+}
+
 static int check_return_code(struct bpf_verifier_env *env, int regno, const char *reg_name)
 {
        const char *exit_ctx = "At program exit";
@@ -17968,35 +17990,21 @@ static int check_return_code(struct bpf_verifier_env *env, int regno, const char
 
        /* LSM and struct_ops func-ptr's return type could be "void" */
        if (!is_subprog || frame->in_exception_callback_fn) {
-               switch (prog_type) {
-               case BPF_PROG_TYPE_LSM:
-                       if (prog->expected_attach_type == BPF_LSM_CGROUP)
-                               /* See return_retval_range, can be 0 or 0-1 depending on hook. */
-                               break;
-                       if (!prog->aux->attach_func_proto->type)
-                               return 0;
-                       break;
-               case BPF_PROG_TYPE_STRUCT_OPS:
-                       if (!prog->aux->attach_func_proto->type)
-                               return 0;
-
-                       if (frame->in_exception_callback_fn)
-                               break;
+               if (program_returns_void(env))
+                       return 0;
+       }
 
-                       /* Allow a struct_ops program to return a referenced kptr if it
-                        * matches the operator's return type and is in its unmodified
-                        * form. A scalar zero (i.e., a null pointer) is also allowed.
-                        */
-                       reg_type = reg->btf ? btf_type_by_id(reg->btf, reg->btf_id) : NULL;
-                       ret_type = btf_type_resolve_ptr(prog->aux->attach_btf,
-                                                       prog->aux->attach_func_proto->type,
-                                                       NULL);
-                       if (ret_type && ret_type == reg_type && reg->ref_obj_id)
-                               return __check_ptr_off_reg(env, reg, regno, false);
-                       break;
-               default:
-                       break;
-               }
+       if (!is_subprog && prog_type == BPF_PROG_TYPE_STRUCT_OPS) {
+               /* Allow a struct_ops program to return a referenced kptr if it
+                * matches the operator's return type and is in its unmodified
+                * form. A scalar zero (i.e., a null pointer) is also allowed.
+                */
+               reg_type = reg->btf ? btf_type_by_id(reg->btf, reg->btf_id) : NULL;
+               ret_type = btf_type_resolve_ptr(prog->aux->attach_btf,
+                                               prog->aux->attach_func_proto->type,
+                                               NULL);
+               if (ret_type && ret_type == reg_type && reg->ref_obj_id)
+                       return __check_ptr_off_reg(env, reg, regno, false);
        }
 
        /* eBPF calling convention is such that R0 is used