tools: bpf_jit_disasm: check for klogctl failure

klogctl can fail and return -ve len, so check for this and
return NULL to avoid passing a (size_t)-1 to malloc.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/net/bpf_jit_disasm.c

@@ -98,6 +98,9 @@ static char *get_klog_buff(unsigned int *klen)
 	char *buff;
 
 	len = klogctl(CMD_ACTION_SIZE_BUFFER, NULL, 0);
+	if (len < 0)
+		return NULL;
+
 	buff = malloc(len);
 	if (!buff)
 		return NULL;