Second CTFs part

lab1_2_recap/01_parrot_cage/main.c

@@ -0,0 +1,48 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdint.h>
+
+__attribute__((noinline))
+void win(void) {
+    char *flag = getenv("FLAG");
+    puts(flag);
+    fflush(stdout);
+    _exit(0);
+}
+
+__attribute__((noinline))
+void vuln(void) {
+    char buf[64];
+
+    puts("=== Polly's Parrot Cage ===\n"
+         "Polly repeats everything you say!\n"
+         "Type a message and Polly will squawk it back.\n"
+         "Say 'bye' when you're done chatting.\n");
+    fflush(stdout);
+
+    for (;;) {
+        ssize_t n = read(STDIN_FILENO, buf, 0x200);
+        if (n < 0) {
+            perror("read");
+            exit(1);
+        }
+        if (n == 0) {
+            break;
+        }
+        if (n >= 3 && buf[0] == 'b' && buf[1] == 'y' && buf[2] == 'e') {
+            break;
+        }
+        puts(buf);
+    }
+}
+
+int main(void) {
+    setvbuf(stdout, NULL, _IONBF, 0);
+    setvbuf(stdin, NULL, _IONBF, 0);
+    vuln();
+    puts("Polly says goodbye! *squawk*");
+    return 0;
+}