bpf: Add missing checks to avoid verbose verifier log

There are a few places where log level is not checked before calling
"verbose()". This forces programs working only at
BPF_LOG_LEVEL_STATS (e.g. veristat) to allocate unnecessarily large
log buffers. Add missing checks.

Reported-by: Emil Tsalapatis <[e-mail]>
Signed-off-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/verifier.c

···
 			return err;
 		}
 
-		verbose(env, "Func#%d ('%s') is global and assumed valid.\n",
-			subprog, sub_name);
+		if (env->log.level & BPF_LOG_LEVEL)
+			verbose(env, "Func#%d ('%s') is global and assumed valid.\n",
+				subprog, sub_name);
 		if (env->subprog_info[subprog].changes_pkt_data)
 			clear_all_pkt_pointers(env);
 		/* mark global subprog for verifying after main prog */
···
 			bt_set_frame_slot(&env->bt, fr, i);
 			first = false;
 		}
-		if (!first)
+		if (!first && (env->log.level & BPF_LOG_LEVEL2))
 			verbose(env, "\n");
 	}
 
···
 		struct bpf_subprog_arg_info *arg;
 		struct bpf_reg_state *reg;
 
-		verbose(env, "Validating %s() func#%d...\n", sub_name, subprog);
+		if (env->log.level & BPF_LOG_LEVEL)
+			verbose(env, "Validating %s() func#%d...\n", sub_name, subprog);
 		ret = btf_prepare_func_args(env, subprog);
 		if (ret)
 			goto out;