bpf: Simplify logging-related error conditions handling

Move log->level == 0 check into bpf_vlog_truncated() instead of doing it
explicitly. Also remove unnecessary goto in kernel/bpf/verifier.c.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-11-andrii@kernel.org

kernel/bpf/btf.c

@@ -5594,7 +5594,7 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size,
 	}
 
 	bpf_vlog_finalize(log);
-	if (log->level && bpf_vlog_truncated(log)) {
+	if (bpf_vlog_truncated(log)) {
 		err = -ENOSPC;
 		goto errout_meta;
 	}

kernel/bpf/log.c

@@ -169,7 +169,9 @@ static int bpf_vlog_reverse_ubuf(struct bpf_verifier_log *log, int start, int en
 
 bool bpf_vlog_truncated(const struct bpf_verifier_log *log)
 {
-	if (log->level & BPF_LOG_FIXED)
+	if (!log->level)
+		return false;
+	else if (log->level & BPF_LOG_FIXED)
 		return bpf_log_used(log) >= log->len_total - 1;
 	else
 		return log->start_pos > 0;

kernel/bpf/verifier.c

@@ -18861,12 +18861,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr)
 	env->prog->aux->verified_insns = env->insn_processed;
 
 	bpf_vlog_finalize(log);
-	if (log->level && bpf_vlog_truncated(log))
+	if (bpf_vlog_truncated(log))
 		ret = -ENOSPC;
-	if (log->level && log->level != BPF_LOG_KERNEL && !log->ubuf) {
+	if (log->level && log->level != BPF_LOG_KERNEL && !log->ubuf)
 		ret = -EFAULT;
-		goto err_release_maps;
-	}
 
 	if (ret)
 		goto err_release_maps;