Commit message: rgw: reject control characters in response-header actions

S3 GetObject permits overriding response header values, but those inputs
need to be validated to insure only characters that are valid in an HTTP
header value are present.

Credit: Initial vulnerability discovery by William Bowling (@wcbowling)
Credit: Further vulnerability discovery by Robin H. Johnson <rjohnson@digitalocean.com>
Signed-off-by: Robin H. Johnson <rjohnson@digitalocean.com>
CVE: CVE-2020-1760
CWE: CWE-79
Vulnerability description: A flaw was found in the Ceph Object Gateway, where it supports request sent by an anonymous user in Amazon S3. This flaw could lead to potential XSS attacks due to the lack of proper neutralization of untrusted input.

Project: ceph
File: rgw_rest_s3.cc

int RGWGetObj_ObjStore_S3::send_response_data(bufferlist& bl, off_t bl_ofs,
					      off_t bl_len)
{
  const char *content_type = NULL;
  string content_type_str;
  map<string, string> response_attrs;
  map<string, string>::iterator riter;
  bufferlist metadata_bl;

  if (sent_header)
    goto send_data;

  if (custom_http_ret) {
    set_req_state_err(s, 0);
    dump_errno(s, custom_http_ret);
  } else {
    set_req_state_err(s, (partial_content && !op_ret) ? STATUS_PARTIAL_CONTENT
                  : op_ret);
    dump_errno(s);
  }

  if (op_ret)
    goto done;

  if (range_str)
    dump_range(s, start, end, s->obj_size);

  if (s->system_request &&
      s->info.args.exists(RGW_SYS_PARAM_PREFIX "prepend-metadata")) {

    dump_header(s, "Rgwx-Object-Size", (long long)total_len);

    if (rgwx_stat) {
      /*
       * in this case, we're not returning the object's content, only the prepended
       * extra metadata
       */
      total_len = 0;
    }

    /* JSON encode object metadata */
    JSONFormatter jf;
    jf.open_object_section("obj_metadata");
    encode_json("attrs", attrs, &jf);
    utime_t ut(lastmod);
    encode_json("mtime", ut, &jf);
    jf.close_section();
    stringstream ss;
    jf.flush(ss);
    metadata_bl.append(ss.str());
    dump_header(s, "Rgwx-Embedded-Metadata-Len", metadata_bl.length());
    total_len += metadata_bl.length();
  }

  if (s->system_request && !real_clock::is_zero(lastmod)) {
    /* we end up dumping mtime in two different methods, a bit redundant */
    dump_epoch_header(s, "Rgwx-Mtime", lastmod);
    uint64_t pg_ver = 0;
    int r = decode_attr_bl_single_value(attrs, RGW_ATTR_PG_VER, &pg_ver, (uint64_t)0);
    if (r < 0) {
      ldout(s->cct, 0) << "ERROR: failed to decode pg ver attr, ignoring" << dendl;
    }
    dump_header(s, "Rgwx-Obj-PG-Ver", pg_ver);

    uint32_t source_zone_short_id = 0;
    r = decode_attr_bl_single_value(attrs, RGW_ATTR_SOURCE_ZONE, &source_zone_short_id, (uint32_t)0);
    if (r < 0) {
      ldout(s->cct, 0) << "ERROR: failed to decode pg ver attr, ignoring" << dendl;
    }
    if (source_zone_short_id != 0) {
      dump_header(s, "Rgwx-Source-Zone-Short-Id", source_zone_short_id);
    }
  }

  for (auto &it : crypt_http_responses)
    dump_header(s, it.first, it.second);

  dump_content_length(s, total_len);
  dump_last_modified(s, lastmod);
  dump_header_if_nonempty(s, "x-amz-version-id", version_id);

  if (! op_ret) {
    if (! lo_etag.empty()) {
      /* Handle etag of Swift API's large objects (DLO/SLO). It's entirerly
       * legit to perform GET on them through S3 API. In such situation,
       * a client should receive the composited content with corresponding
       * etag value. */
      dump_etag(s, lo_etag);
    } else {
      auto iter = attrs.find(RGW_ATTR_ETAG);
      if (iter != attrs.end()) {
        dump_etag(s, iter->second.to_str());
      }
    }

    for (struct response_attr_param *p = resp_attr_params; p->param; p++) {
      bool exists;
      string val = s->info.args.get(p->param, &exists);
      if (exists) {
	/* reject unauthenticated response header manipulation, see
	 * https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html */
	if (s->auth.identity->is_anonymous()) {
	  return -ERR_INVALID_REQUEST;
	}
	if (strcmp(p->param, "response-content-type") != 0) {
	  response_attrs[p->http_attr] = val;
	} else {
	  content_type_str = val;
	  content_type = content_type_str.c_str();
	}
      }
    }

    for (auto iter = attrs.begin(); iter != attrs.end(); ++iter) {
      const char *name = iter->first.c_str();
      map<string, string>::iterator aiter = rgw_to_http_attrs.find(name);
      if (aiter != rgw_to_http_attrs.end()) {
        if (response_attrs.count(aiter->second) == 0) {
          /* Was not already overridden by a response param. */
          response_attrs[aiter->second] = iter->second.c_str();
        }
      } else if (iter->first.compare(RGW_ATTR_CONTENT_TYPE) == 0) {
        /* Special handling for content_type. */
        if (!content_type) {
          content_type = iter->second.c_str();
        }
      } else if (strcmp(name, RGW_ATTR_SLO_UINDICATOR) == 0) {
        // this attr has an extra length prefix from encode() in prior versions
        dump_header(s, "X-Object-Meta-Static-Large-Object", "True");
      } else if (strncmp(name, RGW_ATTR_META_PREFIX,
			 sizeof(RGW_ATTR_META_PREFIX)-1) == 0) {
        /* User custom metadata. */
        name += sizeof(RGW_ATTR_PREFIX) - 1;
        dump_header(s, name, iter->second);
      } else if (iter->first.compare(RGW_ATTR_TAGS) == 0) {
        RGWObjTags obj_tags;
        try{
          bufferlist::iterator it = iter->second.begin();
          obj_tags.decode(it);
        } catch (buffer::error &err) {
          ldout(s->cct,0) << "Error caught buffer::error couldn't decode TagSet " << dendl;
        }
        dump_header(s, RGW_AMZ_TAG_COUNT, obj_tags.count());
      }
    }
  }

done:
  for (riter = response_attrs.begin(); riter != response_attrs.end();
       ++riter) {
    dump_header(s, riter->first, riter->second);
  }

  if (op_ret == -ERR_NOT_MODIFIED) {
      end_header(s, this);
  } else {
      if (!content_type)
          content_type = "binary/octet-stream";

      end_header(s, this, content_type);
  }

  if (metadata_bl.length()) {
    dump_body(s, metadata_bl);
  }
  sent_header = true;

send_data:
  if (get_data && !op_ret) {
    int r = dump_body(s, bl.c_str() + bl_ofs, bl_len);
    if (r < 0)
      return r;
  }

  return 0;
}