Serge Bazanski | 6b649f8 | 2021-05-24 15:09:25 +0200 | [diff] [blame] | 1 | package kubenat |
| 2 | |
| 3 | import ( |
| 4 | "bufio" |
| 5 | "bytes" |
| 6 | "context" |
| 7 | "fmt" |
| 8 | "io/ioutil" |
| 9 | "net" |
| 10 | "strconv" |
| 11 | "strings" |
| 12 | |
| 13 | "github.com/golang/glog" |
| 14 | ) |
| 15 | |
| 16 | // translationReq is a request passed to the translationWorker. |
| 17 | type translationReq struct { |
| 18 | t *Tuple4 |
| 19 | res chan *translationResp |
| 20 | } |
| 21 | |
| 22 | // translationResp is a response from the translationWorker, sent over the res |
| 23 | // channel in a translationReq. |
| 24 | type translationResp struct { |
| 25 | localIP net.IP |
| 26 | localPort uint16 |
| 27 | } |
| 28 | |
| 29 | // reply sends a reply to the given translationReq based on a conntrackEntry, |
| 30 | // sending nil if the entry is nil. |
| 31 | func (r *translationReq) reply(e *conntrackEntry) { |
| 32 | if e == nil { |
| 33 | r.res <- nil |
| 34 | return |
| 35 | } |
| 36 | localPort, err := strconv.ParseUint(e.request["sport"], 10, 16) |
| 37 | if err != nil { |
| 38 | r.res <- nil |
| 39 | return |
| 40 | } |
| 41 | r.res <- &translationResp{ |
| 42 | localIP: net.ParseIP(e.request["src"]), |
| 43 | localPort: uint16(localPort), |
| 44 | } |
| 45 | } |
| 46 | |
| 47 | // translate performs a translationReq/translationResp exchange under a context |
| 48 | // that can be used to time out the query. |
| 49 | func (r *Resolver) translate(ctx context.Context, t *Tuple4) (*translationResp, error) { |
| 50 | resC := make(chan *translationResp, 1) |
| 51 | r.translationC <- &translationReq{ |
| 52 | t: t, |
| 53 | res: resC, |
| 54 | } |
| 55 | |
| 56 | select { |
| 57 | case <-ctx.Done(): |
| 58 | return nil, ctx.Err() |
| 59 | case res := <-resC: |
| 60 | return res, nil |
| 61 | } |
| 62 | } |
| 63 | |
| 64 | // conntrackEntry is an entry parsed from /proc/net/nf_conntrack. The format is |
| 65 | // not well documented, and the best resource I could find is: |
| 66 | // https://stackoverflow.com/questions/16034698/details-of-proc-net-ip-conntrack-and-proc-net-nf-conntrack |
| 67 | type conntrackEntry struct { |
| 68 | // networkProtocol is currently always "ipv4". |
| 69 | networkProtocol string |
| 70 | // transmissionProtocol is currently "tcp" or "udp". |
| 71 | transmissionProtocol string |
| 72 | invalidateTimeout int64 |
| 73 | |
| 74 | state string |
| 75 | |
| 76 | // request key-value pairs. For NAT, these are entries relating to the |
| 77 | // connection as seen as the 'inside' of the NAT, eg. the pod-originated |
| 78 | // connection. |
| 79 | request map[string]string |
| 80 | // response key-value parirs. For NAT, these are entries relating to the |
| 81 | // connection as seen by the 'outside' of the NAT, eg. the internet. |
| 82 | response map[string]string |
| 83 | tags map[string]bool |
| 84 | } |
| 85 | |
| 86 | // conntrackParseEntry parses a line from /proc/net/nf_conntrack into a conntrackEntry. |
| 87 | func conntrackParseEntry(line string) (*conntrackEntry, error) { |
| 88 | entry := conntrackEntry{ |
| 89 | request: make(map[string]string), |
| 90 | response: make(map[string]string), |
| 91 | tags: make(map[string]bool), |
| 92 | } |
| 93 | |
| 94 | fields := strings.Fields(line) |
| 95 | if len(fields) < 5 { |
| 96 | // This should never happen unless the file format drastically |
| 97 | // changed. Don't bother to parse the rest, error early, and let |
| 98 | // someone debug this. |
| 99 | return nil, fmt.Errorf("invalid field count: %v", fields) |
| 100 | } |
| 101 | switch fields[0] { |
| 102 | case "ipv4": |
| 103 | if fields[1] != "2" { |
| 104 | return nil, fmt.Errorf("ipv4 with proto number %q, wanted 2", fields[1]) |
| 105 | } |
| 106 | // TODO(q3k): support IPv6 when we get it on prod. |
| 107 | default: |
| 108 | return nil, nil |
| 109 | } |
| 110 | entry.networkProtocol = fields[0] |
| 111 | |
| 112 | rest := fields[5:] |
| 113 | switch fields[2] { |
| 114 | case "tcp": |
| 115 | if fields[3] != "6" { |
| 116 | return nil, fmt.Errorf("tcp with proto number %q, wanted 6", fields[3]) |
| 117 | } |
| 118 | if len(fields) < 6 { |
| 119 | return nil, fmt.Errorf("tcp with missing state field") |
| 120 | } |
| 121 | entry.state = fields[5] |
| 122 | rest = fields[6:] |
| 123 | case "udp": |
| 124 | if fields[3] != "17" { |
| 125 | return nil, fmt.Errorf("udp with proto number %q, wanted 17", fields[3]) |
| 126 | } |
| 127 | default: |
| 128 | return nil, nil |
| 129 | } |
| 130 | entry.transmissionProtocol = fields[2] |
| 131 | |
| 132 | invalidateTimeout, err := strconv.ParseInt(fields[4], 10, 64) |
| 133 | if err != nil { |
| 134 | return nil, fmt.Errorf("unparseable timeout %q", fields[4]) |
| 135 | } |
| 136 | entry.invalidateTimeout = invalidateTimeout |
| 137 | |
| 138 | for _, el := range rest { |
| 139 | parts := strings.Split(el, "=") |
| 140 | switch len(parts) { |
| 141 | case 1: |
| 142 | // This is a tag. |
| 143 | tag := parts[0] |
| 144 | // Ensure the tag starts and ends with [] (eg. [ASSURED]. |
| 145 | if !strings.HasPrefix(tag, "[") || !strings.HasSuffix(tag, "]") { |
| 146 | continue |
| 147 | } |
| 148 | // Strip [ and ]. |
| 149 | tag = tag[1:] |
| 150 | tag = tag[:len(tag)-1] |
| 151 | if _, ok := entry.tags[tag]; ok { |
| 152 | return nil, fmt.Errorf("repeated tag %q", tag) |
| 153 | } |
| 154 | entry.tags[tag] = true |
| 155 | case 2: |
| 156 | // This is a k/v field. |
| 157 | k := parts[0] |
| 158 | v := parts[1] |
| 159 | if _, ok := entry.request[k]; ok { |
| 160 | if _, ok := entry.response[k]; ok { |
| 161 | return nil, fmt.Errorf("field %q encountered more than twice", k) |
| 162 | } else { |
| 163 | entry.response[k] = v |
| 164 | } |
| 165 | } else { |
| 166 | entry.request[k] = v |
| 167 | } |
| 168 | default: |
| 169 | return nil, fmt.Errorf("unparseable column %q", el) |
| 170 | } |
| 171 | } |
| 172 | return &entry, nil |
| 173 | |
| 174 | } |
| 175 | |
| 176 | // conntrackParse parses the contents of a /proc/net/nf_conntrack file into |
| 177 | // multiple entries. If the majority of the entries could not be parsed, an |
| 178 | // error is returned. |
| 179 | func conntrackParse(data []byte) ([]conntrackEntry, error) { |
| 180 | buf := bytes.NewBuffer(data) |
| 181 | scanner := bufio.NewScanner(buf) |
| 182 | var res []conntrackEntry |
| 183 | var errors []error |
| 184 | for scanner.Scan() { |
| 185 | line := strings.TrimSpace(scanner.Text()) |
| 186 | if line == "" { |
| 187 | continue |
| 188 | } |
| 189 | |
| 190 | entry, err := conntrackParseEntry(line) |
| 191 | if err != nil { |
| 192 | glog.Errorf("Error while parsing %q: %v", line, err) |
| 193 | errors = append(errors, err) |
| 194 | } else if entry != nil { |
| 195 | res = append(res, *entry) |
| 196 | } |
| 197 | } |
| 198 | |
| 199 | if len(errors) == 0 || len(errors) < len(res) { |
| 200 | return res, nil |
| 201 | } else { |
| 202 | return nil, fmt.Errorf("encountered too many errors during conntrack parse, check logs; first error: %w", errors[0]) |
| 203 | } |
| 204 | } |
| 205 | |
| 206 | // contrackIndex is an index into a list of conntrackEntries. It allows lookup |
| 207 | // by request/response k/v pairs. |
| 208 | type conntrackIndex struct { |
| 209 | entries []conntrackEntry |
| 210 | // byRequest is a map from key to value to list of indixes into entries. |
| 211 | byRequest map[string]map[string][]int |
| 212 | // byResponse is a map from key to value to list of indixes into entries. |
| 213 | byResponse map[string]map[string][]int |
| 214 | } |
| 215 | |
| 216 | // buildIndex builds a conntrackIndex from a list of conntrackEntries. |
| 217 | func buildIndex(entries []conntrackEntry) *conntrackIndex { |
| 218 | ix := conntrackIndex{ |
| 219 | entries: entries, |
| 220 | byRequest: make(map[string]map[string][]int), |
| 221 | byResponse: make(map[string]map[string][]int), |
| 222 | } |
| 223 | for i, entry := range ix.entries { |
| 224 | for k, v := range entry.request { |
| 225 | if _, ok := ix.byRequest[k]; !ok { |
| 226 | ix.byRequest[k] = make(map[string][]int) |
| 227 | } |
| 228 | ix.byRequest[k][v] = append(ix.byRequest[k][v], i) |
| 229 | } |
| 230 | for k, v := range entry.response { |
| 231 | if _, ok := ix.byResponse[k]; !ok { |
| 232 | ix.byResponse[k] = make(map[string][]int) |
| 233 | } |
| 234 | ix.byResponse[k][v] = append(ix.byResponse[k][v], i) |
| 235 | } |
| 236 | } |
| 237 | return &ix |
| 238 | } |
| 239 | |
| 240 | // getByRequest returns conntrackEntries that match a given k/v pair in their |
| 241 | // request fields. |
| 242 | func (c *conntrackIndex) getByRequest(k, v string) []*conntrackEntry { |
| 243 | m, ok := c.byRequest[k] |
| 244 | if !ok { |
| 245 | return nil |
| 246 | } |
| 247 | ixes, ok := m[v] |
| 248 | if !ok { |
| 249 | return nil |
| 250 | } |
| 251 | res := make([]*conntrackEntry, len(ixes)) |
| 252 | for i, ix := range ixes { |
| 253 | res[i] = &c.entries[ix] |
| 254 | } |
| 255 | return res |
| 256 | } |
| 257 | |
| 258 | // getByResponse returns conntrackEntries that match a given k/v pair in their |
| 259 | // response fields. |
| 260 | func (c *conntrackIndex) getByResponse(k, v string) []*conntrackEntry { |
| 261 | m, ok := c.byResponse[k] |
| 262 | if !ok { |
| 263 | return nil |
| 264 | } |
| 265 | ixes, ok := m[v] |
| 266 | if !ok { |
| 267 | return nil |
| 268 | } |
| 269 | res := make([]*conntrackEntry, len(ixes)) |
| 270 | for i, ix := range ixes { |
| 271 | res[i] = &c.entries[ix] |
| 272 | } |
| 273 | return res |
| 274 | } |
| 275 | |
| 276 | // find returns a conntrackEntry corresponding to a TCP connection defined on |
| 277 | // the 'outside' of the NAT by a 4-tuple, or nil if no such connection is |
| 278 | // found. |
| 279 | func (c *conntrackIndex) find(t *Tuple4) *conntrackEntry { |
| 280 | // TODO(q3k): support IPv6 |
| 281 | if t.RemoteIP.To4() == nil || t.LocalIP.To4() == nil { |
| 282 | return nil |
| 283 | } |
| 284 | entries := c.getByResponse("src", t.RemoteIP.String()) |
| 285 | for _, entry := range entries { |
| 286 | if entry.transmissionProtocol != "tcp" { |
| 287 | continue |
| 288 | } |
| 289 | if entry.response["sport"] != fmt.Sprintf("%d", t.RemotePort) { |
| 290 | continue |
| 291 | } |
| 292 | if entry.response["dst"] != t.LocalIP.String() { |
| 293 | continue |
| 294 | } |
| 295 | if entry.response["dport"] != fmt.Sprintf("%d", t.LocalPort) { |
| 296 | continue |
| 297 | } |
| 298 | return entry |
| 299 | } |
| 300 | return nil |
| 301 | } |
| 302 | |
| 303 | // runTranslationWorker runs the conntrack 'translation worker'. It responds to |
| 304 | // requests over translationC until ctx is canceled. |
| 305 | func (r *Resolver) runTranslationWorker(ctx context.Context) { |
| 306 | var ix *conntrackIndex |
| 307 | readConntrack := func() { |
| 308 | var entries []conntrackEntry |
| 309 | data, err := ioutil.ReadFile(r.conntrackPath) |
| 310 | if err != nil { |
| 311 | glog.Errorf("Failed to read conntrack file: %v", err) |
| 312 | } else { |
| 313 | entries, err = conntrackParse(data) |
| 314 | if err != nil { |
| 315 | glog.Errorf("failed to parse conntrack entries: %v", err) |
| 316 | } |
| 317 | } |
| 318 | ix = buildIndex(entries) |
| 319 | } |
| 320 | readConntrack() |
| 321 | |
| 322 | for { |
| 323 | select { |
| 324 | case req := <-r.translationC: |
| 325 | entry := ix.find(req.t) |
| 326 | if entry != nil { |
| 327 | req.reply(entry) |
| 328 | } else { |
| 329 | readConntrack() |
| 330 | entry = ix.find(req.t) |
| 331 | if entry != nil { |
| 332 | req.reply(entry) |
| 333 | } else { |
| 334 | req.reply(nil) |
| 335 | } |
| 336 | } |
| 337 | case <-ctx.Done(): |
| 338 | return |
| 339 | } |
| 340 | } |
| 341 | } |