lwip_itoa: check 'bufsize' instead of ignoring it; ensure code is not stolen from GPL

src/core/def.c

@@ -197,26 +197,47 @@ lwip_strnicmp(const char* str1, const char* str2, size_t len)
 void
 lwip_itoa(char* result, size_t bufsize, int number)
 {
-  const int base = 10;
-  char* ptr = result, *ptr1 = result, tmp_char;
-  int tmp_value;
-  LWIP_UNUSED_ARG(bufsize);
+  char *res = result;
+  char *tmp = result;
+  size_t res_left = bufsize;
+  size_t result_len;
+  int n = (number > 0) ? number : -number;
 
-  do {
-    tmp_value = number;
-    number /= base;
-    *ptr++ = "zyxwvutsrqponmlkjihgfedcba9876543210123456789abcdefghijklmnopqrstuvwxyz"[35 + (tmp_value - number * base)];
-  } while(number);
+  /* handle invalid bufsize */
+  if (bufsize < 2) {
+    if (bufsize == 1) {
+      *result = 0;
+    }
+    return;
+  }
 
-   /* Apply negative sign */
-  if (tmp_value < 0) {
-     *ptr++ = '-';
+  /* ensure output string is zero terminated */
+  result[bufsize-1] = 0;
+  result_len = 1;
+  /* create the string in a temporary buffer since we don't know how long
+     it will get */
+  tmp = &result[bufsize-2];
+  while ((n != 0) && (result_len < (result_len - 1))) {
+    char val = '0' + (n % 10);
+    *tmp = val;
+    tmp--;
+    n = n / 10;
+    result_len++;
   }
-  *ptr-- = '\0';
-  while(ptr1 < ptr) {
-    tmp_char = *ptr;
-    *ptr--= *ptr1;
-    *ptr1++ = tmp_char;
+
+  /* output sign first */
+  if (number < 0) {
+    *res = '-';
+    res++;
+    res_left--;
   }
+  if (result_len > res_left) {
+    /* buffer is too small */
+    result[0] = '.';
+    result[1] = 0;
+    return;
+  }
+  /* copy from temporary buffer to output buffer */
+  memmove(res, tmp+1, result_len);
 }
 #endif