Add support for PUID/PGID environment variables

These arefor setting the user/group to drop privileges to.

Closes #2441. Thanks to matthewparkes.

ChangeLog.txt

@@ -59,6 +59,8 @@ Broker:
  before trying to use it in a live broker. Closes #2521.
 - Print messages in mosquitto_passwd when adding/updating passwords.
  Closes #2544.
+- Add support for PUID/PGID environment variables for setting the user/group
+ to drop privileges to. Closes #2441.
 
 Plugins / plugin interface:
 - Add persist-sqlite plugin.

docker/local/docker-entrypoint.sh

@@ -3,8 +3,14 @@ set -e
 
 # Set permissions
 user="$(id -u)"
+if [ "$PUID" = "" ]; then
+ PUID="mosquitto"
+fi
+if [ "$PGID" = "" ]; then
+ PGID="mosquitto"
+fi
 if [ "$user" = '0' ]; then
- [ -d "/mosquitto" ] && chown -R mosquitto:mosquitto /mosquitto || true
+ [ -d "/mosquitto" ] && chown -R ${PUID}:${PGID} /mosquitto || true
 fi
 
 exec "$@"

src/mosquitto.c

@@ -23,6 +23,8 @@ SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 # include <unistd.h>
 # include <grp.h>
 # include <assert.h>
+/* For umask() */
+# include <sys/stat.h>
 #endif
 
 #ifndef WIN32
@@ -65,6 +67,35 @@ int allow_severity = LOG_INFO;
 int deny_severity = LOG_INFO;
 #endif
 
+static int set_umask(void)
+{
+#if !defined(__CYGWIN__) && !defined(WIN32)
+ /* This affects files that are written to, apart from those that are
+ * created using mosquitto_fopen(..., restrict_read=true), which sets a
+ * umask of 077. */
+ const char *mask_s;
+ char *endptr = NULL;
+ long mask;
+
+
+ mask_s = getenv("UMASK_SET");
+ if(mask_s){
+ errno = 0;
+ mask = strtol(mask_s, &endptr, 8);
+ if(errno || endptr == mask_s || *endptr != '\0'){
+ log__printf(NULL, MOSQ_LOG_ERR, "Error: UMASK_SET environment variable not a valid octal number.");
+ return MOSQ_ERR_INVAL;
+ }
+ if(mask < 000 || mask > 0777){
+ log__printf(NULL, MOSQ_LOG_ERR, "Error: UMASK_SET environment variable out of range.");
+ return MOSQ_ERR_INVAL;
+ }
+ umask((mode_t)mask);
+ }
+#endif
+ return MOSQ_ERR_SUCCESS;
+}
+
 /* mosquitto shouldn't run as root.
  * This function will attempt to change to an unprivileged user and group if
  * running as root. The user is given in config->user.
@@ -79,15 +110,43 @@ static int drop_privileges(struct mosquitto__config *config)
  struct passwd *pwd;
  char *err;
  int rc;
+ const char *puid_s, *pgid_s;
+ uid_t puid;
+ gid_t pgid;
 
  const char *snap = getenv("SNAP_NAME");
  if(snap && !strcmp(snap, "mosquitto")){
  /* Don't attempt to drop privileges if running as a snap */
  return MOSQ_ERR_SUCCESS;
  }
 
+ /* PUID and PGID are docker custom user mappings */
+ puid_s = getenv("PUID");
+ pgid_s = getenv("PGID");
+
  if(geteuid() == 0){
- if(config->user && strcmp(config->user, "root")){
+ if(puid_s || pgid_s){
+ if(pgid_s){
+ pgid = (gid_t)atoi(pgid_s);
+
+ rc = setgid(pgid);
+ if(rc == -1){
+ err = strerror(errno);
+ log__printf(NULL, MOSQ_LOG_ERR, "Error setting gid whilst dropping privileges: %s.", err);
+ return 1;
+ }
+ }
+ if(puid_s){
+ puid = (uid_t)atoi(puid_s);
+
+ rc = setuid(puid);
+ if(rc == -1){
+ err = strerror(errno);
+ log__printf(NULL, MOSQ_LOG_ERR, "Error setting uid whilst dropping privileges: %s.", err);
+ return 1;
+ }
+ }
+ }else if(config->user && strcmp(config->user, "root")){
  pwd = getpwnam(config->user);
  if(!pwd){
  if(strcmp(config->user, "mosquitto")){
@@ -283,6 +342,10 @@ int main(int argc, char *argv[])
  */
  rc = drop_privileges(&config);
  if(rc != MOSQ_ERR_SUCCESS) return rc;
+ /* Set umask based on environment variable */
+ rc = set_umask();
+ if(rc != MOSQ_ERR_SUCCESS) return rc;
+
 
  if(config.daemon){
  mosquitto__daemonise();