From: Michael Tremer <michael.tremer@ipfire.org>
Date: Sat, 21 May 2022 14:15:05 +0000 (+0000)
Subject: execute: Use pivot_root instead of chroot
X-Git-Tag: 0.9.28~765
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c9558408cce6191c39780f28fa987ac79b48505b;p=pakfire.git

execute: Use pivot_root instead of chroot

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
---

diff --git a/src/libpakfire/execute.c b/src/libpakfire/execute.c
index b4aab537e..082b04be9 100644
--- a/src/libpakfire/execute.c
+++ b/src/libpakfire/execute.c
@@ -29,6 +29,7 @@
 #include <string.h>
 #include <sys/capability.h>
 #include <sys/epoll.h>
+#include <sys/mount.h>
 #include <sys/personality.h>
 #include <sys/prctl.h>
 #include <sys/types.h>
@@ -82,6 +83,10 @@ struct pakfire_execute_buffer {
 #define __NR_clone3 435
 #endif
 
+static int pivot_root(const char* new_root, const char* put_old) {
+	return syscall(__NR_pivot_root, new_root, put_old);
+}
+
 static int pakfire_execute_buffer_is_full(const struct pakfire_execute_buffer* buffer) {
 	return (sizeof(buffer->data) == buffer->used);
 }
@@ -534,12 +539,15 @@ static int set_environ(struct pakfire_execute* env, const char* key, const char*
 
 static int pakfire_execute_fork(void* data) {
 	struct pakfire_execute* env = (struct pakfire_execute*)data;
+	int r;
 
 	struct pakfire* pakfire = env->pakfire;
 
 	const char* root = pakfire_get_path(pakfire);
 	const char* arch = pakfire_get_arch(pakfire);
 
+	char oldroot[PATH_MAX];
+
 	DEBUG(pakfire, "Execution environment has been forked as PID %d\n", getpid());
 	DEBUG(pakfire, "	root	: %s\n", root);
 	DEBUG(pakfire, "	cgroup  : %s\n", env->cgroup);
@@ -552,23 +560,53 @@ static int pakfire_execute_fork(void* data) {
 
 	// Change root (unless root is /)
 	if (strcmp(root, "/") != 0) {
-		int r = chroot(root);
+		r = pakfire_string_format(oldroot, "%s/.oldroot.XXXXXX", root);
+		if (r < 0) {
+			ERROR(pakfire, "Could not figure out where the old root directory is going: %m\n");
+			return r;
+		}
+
+		// Create temporary directory
+		if (!pakfire_mkdtemp(oldroot)) {
+			ERROR(pakfire, "Could not create temporary directory: %m\n");
+			return r;
+		}
+
+		// Call pivot_root()
+		r = pivot_root(root, oldroot);
 		if (r) {
-			ERROR(pakfire, "chroot() to %s failed: %m\n", root);
+			ERROR(pakfire, "pivot_root() to %s failed: %m\n", root);
 			return 1;
 		}
 
+		// Change directory to /
 		r = chdir("/");
 		if (r) {
 			ERROR(pakfire, "chdir() after chroot() failed: %m\n");
 			return 1;
 		}
+
+		const char* __oldroot = oldroot + strlen(root);
+
+		// Umount the old root directory
+		r = umount2(__oldroot, MNT_DETACH);
+		if (r) {
+			ERROR(pakfire, "Could not umount old root directory: %m\n");
+			return r;
+		}
+
+		// Remove the old root directory
+		r = rmdir(__oldroot);
+		if (r) {
+			ERROR(pakfire, "Could not remove the old root directory: %m\n");
+			return r;
+		}
 	}
 
 	// Set personality
 	unsigned long persona = pakfire_arch_personality(arch);
 	if (persona) {
-		int r = personality(persona);
+		r = personality(persona);
 		if (r < 0) {
 			ERROR(pakfire, "Could not set personality (%x)\n", (unsigned int)persona);
 
@@ -598,7 +636,7 @@ static int pakfire_execute_fork(void* data) {
 	}
 
 	// Reset open file limit (http://0pointer.net/blog/file-descriptor-limits.html)
-	int r = pakfire_rlimit_reset_nofile(pakfire);
+	r = pakfire_rlimit_reset_nofile(pakfire);
 	if (r)
 		return r;
 
diff --git a/src/libpakfire/pakfire.c b/src/libpakfire/pakfire.c
index 744793887..ea7bf2deb 100644
--- a/src/libpakfire/pakfire.c
+++ b/src/libpakfire/pakfire.c
@@ -218,6 +218,13 @@ static int pakfire_mount(struct pakfire* pakfire) {
 	char target[PATH_MAX];
 	int r;
 
+	// Remount / as private
+	r = mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL);
+	if (r) {
+		ERROR(pakfire, "Could not re-mount / as private: %m\n");
+		return r;
+	}
+
 	for (const struct pakfire_mountpoint* mp = mountpoints; mp->source; mp++) {
 		// Skip mounting root when a directory has been passed
 		if (!*mp->target && !pakfire->mount_tmpfs)