fix(dnstap): add bounds for plugin args (#7557)

Validate dnstap writebuffer (MiB) and queue (x10k) args. Reject
non-integers and out-of-range values with clear errors. Updated
plugin documentation and tests.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/dnstap/README.md

@@ -25,11 +25,14 @@ dnstap SOCKET [full] [writebuffer] [queue] {
 
 * **SOCKET** is the socket (path) supplied to the dnstap command line tool.
 * `full` to include the wire-format DNS message.
+* **writebuffer** sets the TCP write buffer multiplier in MiB. Valid range: [1, 1024].
+* **queue** sets the queue multiplier, applied to 10,000 messages. Valid range: [1, 4096].
 * **IDENTITY** to override the identity of the server. Defaults to the hostname.
 * **VERSION** to override the version field. Defaults to the CoreDNS version.
 * **EXTRA** to define "extra" field in dnstap payload, [metadata](../metadata/) replacement available here.
 * `skipverify` to skip tls verification during connection. Default to be secure
 
+
 ## Examples
 
 Log information about client requests and responses to */tmp/dnstap.sock*.
@@ -38,7 +41,7 @@ Log information about client requests and responses to */tmp/dnstap.sock*.
 dnstap /tmp/dnstap.sock
 ~~~
 
-Log information about client requests and responses and tcp write buffer is 1024*Mb and queue is 2048*10000. 
+Log information about client requests and responses with a custom TCP write buffer (1024 MiB) and queue capacity (2048 x 10000).
 
 ~~~ txt
 dnstap /tmp/dnstap.sock full 1024 2048

plugin/dnstap/setup.go

@@ -17,6 +17,14 @@ var log = clog.NewWithPlugin("dnstap")
 
 func init() { plugin.Register("dnstap", setup) }
 
+const (
+	// Upper bounds chosen to keep memory use and kernel socket buffer requests reasonable
+	// while allowing large configurations. Write buffer multiple is in MiB units; queue
+	// multiple is applied to 10,000 messages. See plugin README for parameter semantics.
+	maxMultipleTcpWriteBuf = 1024 // up to 1 GiB write buffer per TCP connection
+	maxMultipleQueue       = 4096 // up to 40,960,000 enqueued messages
+)
+
 func parseConfig(c *caddy.Controller) ([]*Dnstap, error) {
 	dnstaps := []*Dnstap{}
 
@@ -37,11 +45,26 @@ func parseConfig(c *caddy.Controller) ([]*Dnstap, error) {
 		endpoint := args[0]
 
 		if len(args) >= 3 {
-			d.MultipleTcpWriteBuf, _ = strconv.Atoi(args[2])
+			tcpWriteBuf := args[2]
+			if v, err := strconv.Atoi(tcpWriteBuf); err == nil {
+				if v < 1 || v > maxMultipleTcpWriteBuf {
+					return nil, c.Errf("dnstap: MultipleTcpWriteBuf must be between 1 and %d (MiB units): %d", maxMultipleTcpWriteBuf, v)
+				}
+				d.MultipleTcpWriteBuf = v
+			} else {
+				return nil, c.Errf("dnstap: invalid MultipleTcpWriteBuf %q: %v", tcpWriteBuf, err)
+			}
 		}
-
 		if len(args) >= 4 {
-			d.MultipleQueue, _ = strconv.Atoi(args[3])
+			qSize := args[3]
+			if v, err := strconv.Atoi(qSize); err == nil {
+				if v < 1 || v > maxMultipleQueue {
+					return nil, c.Errf("dnstap: MultipleQueue must be between 1 and %d (x10k messages): %d", maxMultipleQueue, v)
+				}
+				d.MultipleQueue = v
+			} else {
+				return nil, c.Errf("dnstap: invalid MultipleQueue %q: %v", qSize, err)
+			}
 		}
 
 		var dio *dio

plugin/dnstap/setup_test.go

@@ -54,6 +54,14 @@ func TestConfig(t *testing.T) {
 		{"dnstap dnstap.sock {\nidentity\n}\n", true, []results{{"dnstap.sock", false, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
 		{"dnstap dnstap.sock {\nversion\n}\n", true, []results{{"dnstap.sock", false, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
 		{"dnstap dnstap.sock {\nextra\n}\n", true, []results{{"dnstap.sock", false, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		// Limits and parsing for writebuffer (MiB) and queue (x10k)
+		{"dnstap dnstap.sock full 1024 2048", false, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1024, 2048}}},
+		{"dnstap dnstap.sock full 1025 1", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		{"dnstap dnstap.sock full 1 4097", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		{"dnstap dnstap.sock full 0 10", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		{"dnstap dnstap.sock full 10 0", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		{"dnstap dnstap.sock full x 10", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
+		{"dnstap dnstap.sock full 10 y", true, []results{{"dnstap.sock", true, "unix", []byte(hostname), []byte("-"), "", 1, 1}}},
 	}
 	for i, tc := range tests {
 		c := caddy.NewTestController("dns", tc.in)