From 4b7af666f2abdf5e3cc76e21b11273deccaec169 Mon Sep 17 00:00:00 2001
From: Evgeny Zinoviev <me@ch1p.io>
Date: Sun, 29 Nov 2020 03:42:28 +0300
Subject: initial

---
 Makefile   |  27 +++++++++++++++++
 glibcrun.c | 101 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 128 insertions(+)
 create mode 100644 Makefile
 create mode 100644 glibcrun.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..4e8c506
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,27 @@
+CC := gcc
+
+PROGRAM = glibcrun
+CFLAGS  = -O2 -std=c99 -Wall -W
+LDFLAGS =
+
+INSTALL = /usr/bin/env install
+PREFIX	= /usr/local
+
+OBJS = glibcrun.o
+
+all: $(PROGRAM)
+
+$(PROGRAM): $(OBJS)
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+install: $(PROGRAM)
+	$(INSTALL) $(PROGRAM) $(PREFIX)/bin
+	chmod u+s $(PREFIX)/bin/${PROGRAM}
+
+clean:
+	rm -f $(OBJS) $(PROGRAM)
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $^ -I. -o $@
+
+.PHONY: all install clean distclean
diff --git a/glibcrun.c b/glibcrun.c
new file mode 100644
index 0000000..efedba1
--- /dev/null
+++ b/glibcrun.c
@@ -0,0 +1,101 @@
+/**
+ * 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;
+}
-- 
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