change name to voidnsrun, add command-line arguments, rewrite readme

4 files changed, 265 insertions, 133 deletions

diff --git a/Makefile b/Makefile
index 4e8c506..050d4ef 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,13 @@
 CC := gcc
 
-PROGRAM = glibcrun
+PROGRAM = voidnsrun
 CFLAGS  = -O2 -std=c99 -Wall -W
 LDFLAGS =
 
 INSTALL = /usr/bin/env install
 PREFIX	= /usr/local
 
-OBJS = glibcrun.o
+OBJS = voidnsrun.o
 
 all: $(PROGRAM)
 
diff --git a/README.md b/README.md
index 4e136d7..6363c9c 100644
--- a/README.md
+++ b/README.md
@@ -1,58 +1,117 @@
-# glibcrun
+# voidnsrun
 
-`glibcrun` is utility for launching glibc linked binaries in isolated namespaces
-in musl-libc Void Linux installations.
+`voidnsrun` is utility for launching programs in an isolated namespace with
+alternative `/usr` tree. Its primary goal is to run glibc-linked binaries in
+musl-libc Void Linux environments or vice-versa.
 
-It creates new private mount namespace for the running process, "replacing" `/usr`
-and `/var/db/xbps` with directories from your glibc basedir using bind
-mounts, and launches your glibc program.
+It creates a new private mount namespace, transparently substitutes `/usr` and 
+some other directories with directories from your alternative root using bind
+mounts, and launches your program.
 
-## Creating glibc chroot
+## Installation
 
-I will use `/glibc` directory name for an example, you can use any other path you
-want.
+Just clone the repo, and then:
 
 ```
-# mkdir /glibc
-# XBPS_ARCH=x86_64 xbps-install --repository=http://alpha.de.repo.voidlinux.org/current -r /glibc -S base-voidstrap
+$ make
+$ sudo make install
 ```
 
-When it's done you may want to chroot into it, e.g. to install some dependencies
-for your glibc software.
+Note that installed binary must be owned by root and have suid bit. `make install`
+should handle it.
 
-## Installing glibcrun
+## Usage
 
-Just clone the repo, and then:
+```
+voidnsrun [OPTIONS] [PROGRAM [ARGS]]
+
+Options:
+	-h:        print this help
+	-m <path>: add bind mount
+	-r <path>: altroot path. If this option is not present,
+	           VOIDNSRUN_DIR environment variable is used.
+	-v:        print version
+```
+
+`voidnsrun` needs to know the path to your alternative root directory and it can
+read it from the `VOIDNSRUN_DIR` environment variable or you can use `-r`
+argument to specify it.
+
+You may want to add something like this to your `~/.bashrc` or similar script:
 
 ```
-$ make
-$ sudo make install
+export VOIDNSRUN_DIR=/glibc
 ```
 
-Note that installed binary must be owned as root and have suid bit. `make install`
-should handle it, but  anyway.
+By default, `voidnsrun` binds these paths from alternative root to the new
+namespace:
+- `/usr`
+- `/var/db/xbps`
+- `/etc/xbps.d`
 
-## Usage
+If you want to mount something else, use `-m` argument.
+
+## Example
 
-`glibcrun` needs to know the path to your glibc base directory and it reads it from
-the `GLIBCRUN_DIR` environment variable. You may want to add something like this
-to your `~/.bashrc` or similar script:
+Let's imagine you want to use some proprietary glibc-linked app on your
+musl-libc Void Linux box. Let it be Vivaldi browser for the example. You
+unpacked it to `/opt/vivaldi` and it doesn't work, obviously.
 
+First, you need to perform an alternative glibc base system installation to a
+separate new directory:
 ```
-export GLIBCRUN_DIR=/glibc
+# mkdir /glibc
+# XBPS_ARCH=x86_64 xbps-install --repository=http://alpha.de.repo.voidlinux.org/current -r /glibc -S base-voidstrap
+```
+
+Export path to this installation for `voidnsrun`:
+```
+export VOIDNSRUN_DIR=/glibc
 ```
 
-When `glibcrun` is run without arguments it will attempt to launch a shell from your
-`SHELL` variable, otherwise it will treat the first argument as a path to an executable
-and the rest as a list of arguments.
+Try launching your app:
+```
+voidnsrun /opt/vivaldi/vivaldi
+```
 
-Example:
+It won't work just yet:
+```
+/opt/vivaldi/vivaldi: error while loading shared libraries: libgobject-2.0.so.0: cannot open shared object file: No such file or directory
+```
+
+Now you need to install all its dependencies into your glibc installation. Use
+`xlocate` from `xtools` package to find a package responsible for a file (or
+just guess it):
+```
+$ xlocate libgobject-2.0.so.0
+Signal-Desktop-1.38.1_1	/usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/sharp/vendor/lib/libgobject-2.0.so -> /usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/sharp/vendor/lib/libgobject-2.0.so.0.5600.4
+Signal-Desktop-1.38.1_1	/usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/sharp/vendor/lib/libgobject-2.0.so.0 -> /usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/sharp/vendor/lib/libgobject-2.0.so.0.5600.4
+Signal-Desktop-1.38.1_1	/usr/lib/signal-desktop/resources/app.asar.unpacked/node_modules/sharp/vendor/lib/libgobject-2.0.so.0.5600.4
+glib-2.66.2_1	/usr/lib/libgobject-2.0.so.0 -> /usr/lib/libgobject-2.0.so.0.6600.2
+glib-2.66.2_1	/usr/lib/libgobject-2.0.so.0.6600.2
+glib-devel-2.66.2_1	/usr/share/gdb/auto-load/usr/lib/libgobject-2.0.so.0.6600.2-gdb.py
+libglib-devel-2.66.2_1	/usr/lib/libgobject-2.0.so -> /usr/lib/libgobject-2.0.so.0
+```
+
+Sync repos and install `glib`. You can use `voidnsrun` for this purpose too.
+Also, I think you should bind `/etc` and `/var` while using `xbps-install` via
+`voidnsrun`, to not mess with your main system files.
+```
+$ sudo voidnsrun -r /glibc -m /etc -m /var xbps-install -Su
+$ sudo voidnsrun -r /glibc -m /etc -m /var xbps-install glib
+```
 
+Try launching vivaldi again:
 ```
-glibcrun /opt/palemoon/palemoon -ProfileManager
+$ voidnsrun /opt/vivaldi/vivaldi
+/opt/vivaldi/vivaldi: error while loading shared libraries: libnss3.so: cannot open shared object file: No such file or directory
 ```
 
-will launch `/opt/palemoon/palemoon -ProfileManager`.
+As you can see, it no longer complains about missing `libgobject-2.0.so.0`, now 
+it's `libnss3.so`. Repeat steps above for all missing dependencies, and in the
+end, it will work. (If it's not, then something's still missing. In particular,
+make sure to install fonts related packages: `xorg-fonts`, `freetype`,
+`fontconfig`, `libXft`.)
 
 ## License
 
diff --git a/glibcrun.c b/glibcrun.c
deleted file mode 100644
index efedba1..0000000
--- a/glibcrun.c
+++ /dev/null
@@ -1,101 +0,0 @@
-/**
- * Copyright (c) 2020 Evgeny Zinoviev <me@ch1p.io>. 
- * 
- * This program is licensed under the BSD 2-Clause License.
- * https://opensource.org/licenses/BSD-2-Clause
- */
-
-#define _GNU_SOURCE
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <unistd.h>
-#include <errno.h>
-#include <sched.h>
-#include <sys/mount.h>
-#include <sys/stat.h>
-#include <linux/limits.h>
-
-const char *var_name = "GLIBCRUN_DIR";
-
-#define ARRAY_SIZE(x)  (sizeof(x) / sizeof((x)[0]))
-#define ERROR(f_, ...) fprintf(stderr, (f_), ##__VA_ARGS__)
-
-int main(int argc, char *argv[]) {
-    int result;
-
-    /* Get glibc base path */
-    const char *dir = getenv(var_name);
-    if (!dir) {
-        ERROR("error: environment variable %s not found.\n", var_name);
-        return 1;
-    }
-
-    /* Validate it */
-    struct stat st;
-    result = stat(dir, &st);
-    if (result != 0 || !S_ISDIR(st.st_mode)) {
-        ERROR("error: %s is not a directory.\n", dir);
-        return 1;
-    }
-
-    /* Get shell from current env to reuse it if needed */
-    const char *shell = getenv("SHELL");
-    if (!shell)
-        shell = "/bin/sh";
-
-    /* Do the unshare magic */
-    result = unshare(CLONE_NEWNS);
-    if (result == -1) {
-        ERROR("unshare: %s\n", strerror(errno));
-        return 1;
-    }
-
-    /* Mount glibc stuff to our private namespace */
-    const char *const mountpoints[] = {"/usr", "/var/db/xbps"};
-    char buf[PATH_MAX];
-
-    for (int i = 0; i < (int)ARRAY_SIZE(mountpoints); i++) {
-        strcpy(buf, dir);
-        strcat(buf, mountpoints[i]);
-        result = mount(buf, mountpoints[i], NULL, MS_BIND|MS_REC, NULL);
-        if (result == -1) {
-            ERROR("mount(%s): %s\n", mountpoints[i], strerror(errno));
-            return 1;
-        }
-    }
-
-    /* Drop root */
-    uid_t uid = getuid();
-    gid_t gid = getgid();
-
-    result = setreuid(uid, uid);
-    if (result == -1) {
-        ERROR("setreuid: %s\n", strerror(errno));
-        return 1;
-    }
-
-    result = setregid(gid, gid);
-    if (result == -1) {
-        ERROR("setregid: %s\n", strerror(errno));
-        return 1;
-    }
-
-    /* Launch program or shell */
-    const char *exec_cmd;
-    char *const *exec_args = NULL;
-    if (argc < 2)
-        exec_cmd = shell;
-    else {
-        exec_cmd = argv[1];
-        exec_args = (char *const *)argv+1;
-    }
-
-    result = execvp(exec_cmd, exec_args);
-    if (result == -1) {
-        ERROR("execvp(%s): %s\n", exec_cmd, strerror(errno));
-        return 1;
-    }
-
-    return 0;
-}
diff --git a/voidnsrun.c b/voidnsrun.c
new file mode 100644
index 0000000..e121c0f
--- /dev/null
+++ b/voidnsrun.c
@@ -0,0 +1,174 @@
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <linux/limits.h>
+
+const char *var_name = "VOIDNSRUN_DIR";
+const char *prog_version = "1.0";
+
+#define USERMOUNTS_MAX 8
+
+#define ARRAY_SIZE(x)  (sizeof(x) / sizeof((x)[0]))
+#define ERROR(f_, ...) fprintf(stderr, (f_), ##__VA_ARGS__)
+
+bool isdir(const char *s)
+{
+	struct stat st;
+	int result = stat(s, &st);
+	if (result == -1)
+		ERROR("stat: %s\n", strerror(errno));
+	return result == 0 && S_ISDIR(st.st_mode);
+}
+
+void usage(const char *progname)
+{
+	printf("Usage: %s [OPTIONS] [PROGRAM [ARGS]]\n", progname);
+	printf("\n"
+			"Options:\n"
+			"	-h:        print this help\n"
+			"	-m <path>: add bind mount\n"
+			"	-r <path>: altroot path. If this option is not present,\n"
+			"	           %s environment variable is used.\n"
+			"	-v:        print version\n",
+			var_name);
+}
+
+bool mount_list(
+	const char *dirptr,
+	size_t dirlen,
+	const char **mountpoints,
+	size_t len,
+	bool ignore_missing)
+{
+	char buf[PATH_MAX];
+	for (size_t i = 0; i < len; i++) {
+		/* Check if it's safe to proceed. */
+		if (dirlen + strlen(mountpoints[i]) >= PATH_MAX) {
+			ERROR("error: path %s%s is too large.\n", dirptr, mountpoints[i]);
+			return false;
+		}
+		strcpy(buf, dirptr);
+		strcat(buf, mountpoints[i]);
+		if (!isdir(buf)) {
+			if (!ignore_missing) {
+				ERROR("error: source mount dir %s does not exists.\n", buf);
+				return false;
+			} else
+				continue;
+		}
+		if (!isdir(mountpoints[i])) {
+			ERROR("error: mountpoint %s does not exists.\n", mountpoints[i]);
+			return false;
+		}
+		if (mount(buf, mountpoints[i], NULL, MS_BIND|MS_REC, NULL) == -1) {
+			ERROR("mount: failed to mount %s: %s\n",
+				mountpoints[i], strerror(errno));
+			return false;
+		}
+	}
+	return true;
+}
+
+int main(int argc, char **argv)
+{
+	if (argc < 2) {
+		usage(argv[0]);
+		return 0;
+	}
+	
+	int result;
+	char *dir = NULL;
+	size_t dirlen;
+	const char *usermounts[USERMOUNTS_MAX] = {0};
+	int usermounts_count = 0;
+	int c;
+	while ((c = getopt(argc, argv, "vhm:r:")) != -1) {
+		switch (c) {
+			case 'v':
+				printf("%s\n", prog_version);
+				return 0;
+			case 'h':
+				usage(argv[0]);
+				return 0;
+			case 'r':
+				dir = optarg;
+				break;
+			case 'm':
+				if (usermounts_count < USERMOUNTS_MAX) {
+					usermounts[usermounts_count++] = optarg;
+					break;
+				} else {
+					ERROR("error: only up to %d user mounts allowed.\n",
+						USERMOUNTS_MAX);
+					return 1;
+				}
+			case '?':
+				return 1;
+		}
+	}
+
+	/* Get alternative root dir. */
+	if (!dir)
+		dir = getenv(var_name);
+	if (!dir) {
+		ERROR("error: environment variable %s not found.\n", var_name);
+		return 1;
+	}
+
+	/* Validate it. */
+	if (!isdir(dir)) {
+		ERROR("error: %s is not a directory.\n", dir);
+		return 1;
+	}
+	
+	dirlen = strlen(dir);
+
+	/* Do the unshare magic. */
+	result = unshare(CLONE_NEWNS);
+	if (result == -1) {
+		ERROR("unshare: %s\n", strerror(errno));
+		return 1;
+	}
+
+	/* Mount stuff from altroot to our private namespace. */
+	const char *mountpoints[] = {"/usr", "/var/db/xbps", "/etc/xbps.d"};
+	
+	if (!mount_list(dir, dirlen, mountpoints, ARRAY_SIZE(mountpoints), true))
+		return 1;
+	
+	if (usermounts_count > 0 && 
+		!mount_list(dir, dirlen, usermounts, usermounts_count, false))
+		return 1;
+
+	/* Drop root. */
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+
+	result = setreuid(uid, uid);
+	if (result == -1) {
+		ERROR("setreuid: %s\n", strerror(errno));
+		return 1;
+	}
+
+	result = setregid(gid, gid);
+	if (result == -1) {
+		ERROR("setregid: %s\n", strerror(errno));
+		return 1;
+	}
+	
+	/* Launch program. */
+	result = execvp(argv[optind], (char *const *)argv+optind);
+	if (result == -1) {
+		ERROR("execvp(%s): %s\n", argv[optind], strerror(errno));
+		return 1;
+	}
+
+	return 0;
+}