bpf: drop unnecessary user-triggerable WARN_ONCE in verifierl log

It's trivial for user to trigger "verifier log line truncated" warning,
as verifier has a fixed-sized buffer of 1024 bytes (as of now), and there are at
least two pieces of user-provided information that can be output through
this buffer, and both can be arbitrarily sized by user:
  - BTF names;
  - BTF.ext source code lines strings.

Verifier log buffer should be properly sized for typical verifier state
output. But it's sort-of expected that this buffer won't be long enough
in some circumstances. So let's drop the check. In any case code will
work correctly, at worst truncating a part of a single line output.

Reported-by: syzbot+8b2a08dfbd25fd933d75@syzkaller.appspotmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230516180409.3549088-1-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/log.c

@@ -62,9 +62,6 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt,
 
 	n = vscnprintf(log->kbuf, BPF_VERIFIER_TMP_LOG_SIZE, fmt, args);
 
-	WARN_ONCE(n >= BPF_VERIFIER_TMP_LOG_SIZE - 1,
-		  "verifier log line truncated - local buffer too short\n");
-
 	if (log->level == BPF_LOG_KERNEL) {
 		bool newline = n > 0 && log->kbuf[n - 1] == '\n';