bpf: Remove minimum size restrictions on verifier log buffer

It's not clear why we have 128 as minimum size, but it makes testing
harder and seems unnecessary, as we carefully handle truncation
scenarios and use proper snprintf variants. So remove this limitation
and just enforce positive length for log buffer.

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/20230406234205.323208-3-andrii@kernel.org

kernel/bpf/log.c

@@ -11,7 +11,7 @@
 
 bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log)
 {
-	return log->len_total >= 128 && log->len_total <= UINT_MAX >> 2 &&
+	return log->len_total > 0 && log->len_total <= UINT_MAX >> 2 &&
 	       log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK);
 }