bpf: Wrap register invalidation with a helper

Typically, verifier should use env->allow_ptr_leaks when invaliding
registers for users that don't have CAP_PERFMON or CAP_SYS_ADMIN to
avoid leaking the pointer value. This is similar in spirit to
c67cae5 ("bpf: Tighten ptr_to_btf_id checks."). In a lot of the
existing checks, we know the capabilities are present, hence we don't do
the check.

Instead of being inconsistent in the application of the check, wrap the
action of invalidating a register into a helper named 'mark_invalid_reg'
and use it in a uniform fashion to replace open coded invalidation
operations, so that the check is always made regardless of the call site
and we don't have to remember whether it needs to be done or not for
each case.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230221200646.2500777-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: kkdwvd

kernel/bpf/verifier.c

@@ -895,6 +895,14 @@ static int unmark_stack_slots_dynptr(struct bpf_verifier_env *env, struct bpf_re
 static void __mark_reg_unknown(const struct bpf_verifier_env *env,
 			       struct bpf_reg_state *reg);
 
+static void mark_reg_invalid(const struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+{
+	if (!env->allow_ptr_leaks)
+		__mark_reg_not_init(env, reg);
+	else
+		__mark_reg_unknown(env, reg);
+}
+
 static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
 				        struct bpf_func_state *state, int spi)
 {
@@ -934,12 +942,8 @@ static int destroy_if_dynptr_stack_slot(struct bpf_verifier_env *env,
 		/* Dynptr slices are only PTR_TO_MEM_OR_NULL and PTR_TO_MEM */
 		if (dreg->type != (PTR_TO_MEM | PTR_MAYBE_NULL) && dreg->type != PTR_TO_MEM)
 			continue;
-		if (dreg->dynptr_id == dynptr_id) {
-			if (!env->allow_ptr_leaks)
-				__mark_reg_not_init(env, dreg);
-			else
-				__mark_reg_unknown(env, dreg);
-		}
+		if (dreg->dynptr_id == dynptr_id)
+			mark_reg_invalid(env, dreg);
 	}));
 
 	/* Do not release reference state, we are destroying dynptr on stack,
@@ -7384,7 +7388,7 @@ static void clear_all_pkt_pointers(struct bpf_verifier_env *env)
 
 	bpf_for_each_reg_in_vstate(env->cur_state, state, reg, ({
 		if (reg_is_pkt_pointer_any(reg))
-			__mark_reg_unknown(env, reg);
+			mark_reg_invalid(env, reg);
 	}));
 }
 
@@ -7429,12 +7433,8 @@ static int release_reference(struct bpf_verifier_env *env,
 		return err;
 
 	bpf_for_each_reg_in_vstate(env->cur_state, state, reg, ({
-		if (reg->ref_obj_id == ref_obj_id) {
-			if (!env->allow_ptr_leaks)
-				__mark_reg_not_init(env, reg);
-			else
-				__mark_reg_unknown(env, reg);
-		}
+		if (reg->ref_obj_id == ref_obj_id)
+			mark_reg_invalid(env, reg);
 	}));
 
 	return 0;
@@ -7447,7 +7447,7 @@ static void invalidate_non_owning_refs(struct bpf_verifier_env *env)
 
 	bpf_for_each_reg_in_vstate(env->cur_state, unused, reg, ({
 		if (type_is_non_owning_ref(reg->type))
-			__mark_reg_unknown(env, reg);
+			mark_reg_invalid(env, reg);
 	}));
 }