utils: add uid, gid, group convenience wrappers

src/lxc/utils.c

@@ -26,6 +26,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <grp.h>
 #include <libgen.h>
 #include <stddef.h>
 #include <stdio.h>
@@ -2053,3 +2054,32 @@ int lxc_safe_long(const char *numstr, long int *converted)
 	*converted = sli;
 	return 0;
 }
+
+int lxc_switch_uid_gid(uid_t uid, gid_t gid)
+{
+	if (setgid(gid) < 0) {
+		SYSERROR("Failed to switch to gid %d.", gid);
+		return -errno;
+	}
+	NOTICE("Switched to gid %d.", gid);
+
+	if (setuid(uid) < 0) {
+		SYSERROR("Failed to switch to uid %d.", uid);
+		return -errno;
+	}
+	NOTICE("Switched to uid %d.", uid);
+
+	return 0;
+}
+
+/* Simple covenience function which enables uniform logging. */
+int lxc_setgroups(int size, gid_t list[])
+{
+	if (setgroups(size, list) < 0) {
+		SYSERROR("Failed to setgroups().");
+		return -errno;
+	}
+	NOTICE("Dropped additional groups.");
+
+	return 0;
+}

src/lxc/utils.h

@@ -327,4 +327,8 @@ int lxc_safe_uint(const char *numstr, unsigned int *converted);
 int lxc_safe_int(const char *numstr, int *converted);
 int lxc_safe_long(const char *numstr, long int *converted);
 
+/* Switch to a new uid and gid. */
+int lxc_switch_uid_gid(uid_t uid, gid_t gid);
+int lxc_setgroups(int size, gid_t list[]);
+
 #endif /* __LXC_UTILS_H */