[PATCH v2] resolv: Add test for gethostbyname_r unaligned buffer [BZ #18287]

[Florian Weimer]

* Sergey Kolosov:

> +/* Test gethostbyname_r with a specified buffer size and alignment.
> +   Returns true if the buffer is sufficient, false if it's too small.  */
> +static bool
> +query_host (const char *host_name, size_t size, size_t align)
> +{
> +  struct hostent ret;
> +  struct hostent *result;
> +  int err;
> +
> +  /* Allocate memory for buffer, alignment padding, and a 64-byte checking area.  */

I think this line is now longer than 79 characters.  Please wrap.

> +  size_t total_alloc = size + align + 64;
> +  unsigned char *raw_buf = xmalloc (total_alloc);
> +
> +  /* Fill in buffer with 0xAA to detect buffer overflow.  */

Suggest: Fill the tail of the buffer with 0xAA to dewtect overflows below.

> +  memset (raw_buf, 0, size + align);
> +  memset (raw_buf + size + align, 0xAA, 64);
> +
> +  char *ptr = (char *) raw_buf + align;
> +
> +  int res = gethostbyname_r (host_name, &ret, ptr, size, &result, &err);
> +
> +  /* Verify that the overflow guard region remains unchanged.  */
> +  bool overflow_detected = false;
> +  for (int i = 0; i < 64; i++)
> +    {
> +      if (raw_buf[size + align + i] != 0xAA)
> +        {
> +          overflow_detected = true;
> +          break;
> +        }
> +    }
> +
> +  if (overflow_detected)
> +    {
> +      free (raw_buf);
> +      FAIL_EXIT1 ("Buffer overflow was detected! (align=%zu, size=%zu)\n",
> +                  align, size);
> +    }

The free is superfluous (we generally do not clean up memory before
FAIL_EXIT1), and I think this can move into the for loop above.

> +  if (res == 0 && result != NULL)
> +    {
> +      /* Generate the expected response to satisfy check_hostent.  */
> +      char expected_response[4096];
> +      strcpy (expected_response, "name: foo.site.example\n");
> +      for (int i = 0; i <= 60; i++)
> +        {
> +          char buf[64];
> +          snprintf (buf, sizeof (buf), "address: 127.126.125.%d\n", i);
> +          strcat (expected_response, buf);
> +        }
> +
> +      check_hostent (host_name, &ret, expected_response);
> +      is_sufficient = true; /* Buffer is sufficient.  */

I'd use fprintf with xopen_memstream.

Thanks,
Florian