Add possibility for priviledge drop

Adds the `uid` and `gid` settings in the main configuration file, which
allows weblug to run under a unprivileged user account. This comes with
the limitation, that unless the program runs as root, custom webhook
`uid/gid` settings are not possible.

cmd/weblug/config.go

@@ -14,6 +14,8 @@ type Config struct {
 
 type ConfigSettings struct {
 	BindAddress string `yaml:"bind"` // Bind address for the webserver
+	UID         int    `yaml:"uid"`  // Custom user ID or 0, if not being used
+	GID         int    `yaml:"gid"`  // Custom group ID or 0, if not being used
 }
 
 func (cf *Config) SetDefaults() {

cmd/weblug/weblug.go

@@ -38,7 +38,11 @@ func awaitTerminationSignal() {
 
 // Perform sanity check on hooks
 func sanityCheckHooks(hooks []Hook) error {
-	uid := os.Getuid()
+	// Check UID and GID settings. When hooks have their own UID and GID settings, we need the main program to run as root (required for setgid/setuid)
+	uid := cf.Settings.UID
+	if uid == 0 {
+		uid = os.Getuid()
+	}
 	for _, hook := range hooks {
 		// If a hook sets a custom uid or gid, ensure we're running as root, otherwise print a warning
 		if hook.UID != 0 && uid != 0 {
@@ -81,6 +85,20 @@ func main() {
 		os.Exit(3)
 	}
 
+	// Drop privileges?
+	if cf.Settings.GID != 0 {
+		if err := syscall.Setgid(cf.Settings.GID); err != nil {
+			fmt.Fprintf(os.Stderr, "setgid failed: %s\n", err)
+			os.Exit(1)
+		}
+	}
+	if cf.Settings.UID != 0 {
+		if err := syscall.Setuid(cf.Settings.UID); err != nil {
+			fmt.Fprintf(os.Stderr, "setuid failed: %s\n", err)
+			os.Exit(1)
+		}
+	}
+
 	// Create default handlers
 	http.HandleFunc("/health", createHealthHandler())
 	http.HandleFunc("/health.json", createHealthHandler())

doc/weblug.8

@@ -46,6 +46,10 @@ See the following example configuration file:
 .br
 .B "  bind: ":2088"              # bind to all addresses
 .br
+.B "  uid: 0                     # run under specified user id
+.br
+.B "  gid: 0                     # run under specified group id
+.br
 .B "# hook definitions. A hook needs to define the HTTP endpoint ("route") and the command
 .br
 .B "# See the following examples for more possible options.

test/blackbox.sh

@@ -19,6 +19,7 @@ export SECRET1="top5ecret"
 
 rm -f testfile
 ../weblug test.yaml &
+../weblug test_uid.yaml &
 sleep 1
 
 ## Check touch webhook, which creates "testfile"
@@ -60,7 +61,14 @@ fi
 
 ## Check environment variables
 
-
 timeout 10 curl --fail 'http://127.0.0.1:2088/env'
 
+
+## Check UID/GID handling
+
+# Ensure weblug is running with UID=65534
+pgrep -u 65534 weblug
+# Ensure weblug2 (test_uid) is actually running
+timeout 10 curl --fail 'http://127.0.0.1:2089/uid'
+
 echo -e "\n\nall good"

test/test_uid.yaml

@@ -0,0 +1,11 @@
+---
+settings:
+  bind: "127.0.0.1:2089"    # bind address for webserver
+  uid: 65534
+  gid: 65534
+
+hooks:
+  - name: 'uid hook'
+    route: "/uid"
+    command: "id -u"
+    output: True

weblug.yml

@@ -4,6 +4,10 @@
 settings:
   #bind: "127.0.0.1:2088"    # bind address for webserver
   bind: ":2088"              # bind to all addresses
+  # Note: Due to current limitations, weblug needs to run as root when you use custom uid,gid settings per webhook
+  # This is a known issue, see https://codeberg.org/grisu48/weblug/issues/9
+  uid: 0                     # run under specified user id
+  gid: 0                     # run under specified group id
 
 # hook definitions. A hook needs to define the HTTP endpoint ("route") and the command
 # See the following examples for more possible options.