Commit message: ssh: fixing unsigned overflow leading to heap overflow

cf GHSL-2020-051
CVE: CVE-2020-11939
CWE: CWE-190
Vulnerability description: In nDPI through 3.2 Stable, the SSH protocol dissector has multiple KEXINIT integer overflows that result in a controlled remote heap overflow in concat_hash_string in ssh.c. Due to the granular nature of the overflow primitive and the ability to control both the contents and layout of the nDPI library's heap memory through remote input, this vulnerability may be abused to achieve full Remote Code Execution against any network inspection stack that is linked against nDPI and uses it to perform network traffic analysis.

Project: nDPI
File: ssh.c

static u_int16_t concat_hash_string(struct ndpi_packet_struct *packet,
				   char *buf, u_int8_t client_hash) {
  u_int16_t offset = 22, buf_out_len = 0;
  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  u_int32_t len = ntohl(*(u_int32_t*)&packet->payload[offset]);
  offset += 4;

  /* -1 for ';' */
  if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
    goto invalid_payload;

  /* ssh.kex_algorithms [C/S] */
  strncpy(buf, (const char *)&packet->payload[offset], buf_out_len = len);
  buf[buf_out_len++] = ';';
  offset += len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.server_host_key_algorithms [None] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);
  offset += 4 + len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.encryption_algorithms_client_to_server [C] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    buf[buf_out_len++] = ';';
    offset += len;
  } else
    offset += 4 + len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.encryption_algorithms_server_to_client [S] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(!client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    buf[buf_out_len++] = ';';
    offset += len;
  } else
    offset += 4 + len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.mac_algorithms_client_to_server [C] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    buf[buf_out_len++] = ';';
    offset += len;
  } else
    offset += 4 + len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.mac_algorithms_server_to_client [S] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(!client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    buf[buf_out_len++] = ';';
    offset += len;
  } else
    offset += 4 + len;

  /* ssh.compression_algorithms_client_to_server [C] */
  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    offset += len;
  } else
    offset += 4 + len;

  if(offset+sizeof(u_int32_t) >= packet->payload_packet_len)
    goto invalid_payload;
  /* ssh.compression_algorithms_server_to_client [S] */
  len = ntohl(*(u_int32_t*)&packet->payload[offset]);

  if(!client_hash) {
    offset += 4;

    if((offset >= packet->payload_packet_len) || (len >= packet->payload_packet_len-offset-1))
      goto invalid_payload;

    strncpy(&buf[buf_out_len], (const char *)&packet->payload[offset], len);
    buf_out_len += len;
    offset += len;
  } else
    offset += 4 + len;

  /* ssh.languages_client_to_server [None] */

  /* ssh.languages_server_to_client [None] */

#ifdef SSH_DEBUG
  printf("[SSH] %s\n", buf);
#endif

  return(buf_out_len);

invalid_payload:

#ifdef SSH_DEBUG
  printf("[SSH] Invalid packet payload\n");
#endif

  return(0);
}