procd: detect lxc container and behave accordingly

meaning to not mount some specific parts witch cause trouble.

The patch is based on previous work of @mikma to combine OpenWrt with
lxd[0]. This patch however adds a detection copied from *virt-what* to
check /proc/1/environment for the string "container".

Thanks to @dangowrt for the cleanup.

[0]: https://github.com/containercraft/openwrt-lxd/blob/master/patches/procd-openwrt-18.06/001_lxd_no_mounts.patch

Signed-off-by: Paul Spooren <mail@aparcar.org>

4 files changed, 50 insertions, 17 deletions

diff --git a/container.h b/container.h
new file mode 100644
index 0000000..7fb0768
--- /dev/null
+++ b/container.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2019 Paul Spooren <mail@aparcar.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2.1
+ * as published by the Free Software Foundation
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef __CONTAINER_H
+#define __CONTAINER_H
+#include <stdlib.h>
+
+static inline bool is_container() {
+	return !!getenv("container");
+}
+
+#endif
diff --git a/initd/early.c b/initd/early.c
index 2e15112..7b281b2 100644
--- a/initd/early.c
+++ b/initd/early.c
@@ -25,6 +25,7 @@
 #include "../utils/utils.h"
 #include "init.h"
 #include "../libc-compat.h"
+#include "../container.h"
 
 static void
 early_dev(void)
@@ -56,14 +57,17 @@ early_mounts(void)
 {
 	unsigned int oldumask = umask(0);
 
-	mount("proc", "/proc", "proc", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
-	mount("sysfs", "/sys", "sysfs", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
-	mount("cgroup", "/sys/fs/cgroup", "cgroup",  MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
-	mount("tmpfs", "/dev", "tmpfs", MS_NOATIME | MS_NOSUID, "mode=0755,size=512K");
-	ignore(symlink("/tmp/shm", "/dev/shm"));
-	mkdir("/dev/pts", 0755);
-	mount("devpts", "/dev/pts", "devpts", MS_NOATIME | MS_NOEXEC | MS_NOSUID, "mode=600");
-	early_dev();
+	if (!is_container()) {
+		mount("proc", "/proc", "proc", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
+		mount("sysfs", "/sys", "sysfs", MS_NOATIME | MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
+		mount("cgroup", "/sys/fs/cgroup", "cgroup",  MS_NODEV | MS_NOEXEC | MS_NOSUID, 0);
+		mount("tmpfs", "/dev", "tmpfs", MS_NOATIME | MS_NOSUID, "mode=0755,size=512K");
+		ignore(symlink("/tmp/shm", "/dev/shm"));
+		mkdir("/dev/pts", 0755);
+		mount("devpts", "/dev/pts", "devpts", MS_NOATIME | MS_NOEXEC | MS_NOSUID, "mode=600");
+
+		early_dev();
+	}
 
 	early_console("/dev/console");
 	if (mount_zram_on_tmp()) {
diff --git a/initd/zram.c b/initd/zram.c
index b41bfd9..487d3d6 100644
--- a/initd/zram.c
+++ b/initd/zram.c
@@ -12,6 +12,7 @@
 #include <sys/stat.h>
 
 #include "../log.h"
+#include "../container.h"
 
 #include "init.h"
 
@@ -116,10 +117,12 @@ mount_zram_on_tmp(void)
 		waitpid(pid, NULL, 0);
 	}
 
-	ret = mount("/dev/zram0", "/tmp", "ext4", MS_NOSUID | MS_NODEV | MS_NOATIME, "errors=continue,noquota");
-	if (ret < 0) {
-		ERROR("Can't mount /dev/zram0 on /tmp: %m\n");
-		return errno;
+	if (!is_container()) {
+		ret = mount("/dev/zram0", "/tmp", "ext4", MS_NOSUID | MS_NODEV | MS_NOATIME, "errors=continue,noquota");
+		if (ret < 0) {
+			ERROR("Can't mount /dev/zram0 on /tmp: %m\n");
+			return errno;
+		}
 	}
 
 	LOG("Using up to %ld kB of RAM as ZRAM storage on /mnt\n", zramsize);
diff --git a/plug/coldplug.c b/plug/coldplug.c
index c6a89c3..12df421 100644
--- a/plug/coldplug.c
+++ b/plug/coldplug.c
@@ -22,6 +22,7 @@
 #include "../libc-compat.h"
 
 #include "hotplug.h"
+#include "../container.h"
 
 static struct uloop_process udevtrigger;
 
@@ -43,13 +44,16 @@ void procd_coldplug(void)
 	char *argv[] = { "udevtrigger", NULL };
 	unsigned int oldumask = umask(0);
 
-	umount2("/dev/pts", MNT_DETACH);
-	umount2("/dev/", MNT_DETACH);
-	mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755,size=512K");
+	if (!is_container()) {
+		umount2("/dev/pts", MNT_DETACH);
+		umount2("/dev/", MNT_DETACH);
+		mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755,size=512K");
+		mkdir("/dev/pts", 0755);
+		mount("devpts", "/dev/pts", "devpts", MS_NOEXEC | MS_NOSUID, 0);
+	}
+
 	ignore(symlink("/tmp/shm", "/dev/shm"));
-	mkdir("/dev/pts", 0755);
 	umask(oldumask);
-	mount("devpts", "/dev/pts", "devpts", MS_NOEXEC | MS_NOSUID, 0);
 	udevtrigger.cb = udevtrigger_complete;
 	udevtrigger.pid = fork();
 	if (!udevtrigger.pid) {