From 68f78d914b221763476e6f17a0d0c48183eeb8cb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Karel=20Ko=C4=8D=C3=AD?= <cynerd@email.cz>
Date: Sun, 28 Apr 2019 17:56:30 +0200
Subject: child: allow binfmt_misc to be preserved

This should allow chrooting to non-native systems using qemu.
---
 child.c | 21 ++++++++++++---------
 child.h |  2 ++
 main.c  | 13 ++++++++++++-
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/child.c b/child.c
index a9c5c26..d25df85 100644
--- a/child.c
+++ b/child.c
@@ -27,24 +27,27 @@
 #include <assert.h>
 #include "utils.h"
 
+#define PROC_BINFMT "/proc/sys/fs/binfmt_misc"
+
 int child_main(void *_args) {
 	struct child_args *args = _args;
 	sigpipe_wait(args->sigpipe);
 
-	// Change some mount points to private
+	// Change all mount points to private
 	mount("none", "/", NULL, MS_REC | MS_PRIVATE, NULL);
 	assert_perror(errno);
-	/*
-	mount("none", "/proc", NULL, MS_REC | MS_PRIVATE, NULL);
-	assert_perror(errno);
-	mount("none", "/sys", NULL, MS_REC | MS_PRIVATE, NULL);
-	assert_perror(errno);
-	*/
+
 	// Mount new proc filesystem for this namespace
+	if (args->binfmt) {
+		mount(PROC_BINFMT, "/tmp", NULL, MS_BIND, NULL); 
+		assert_perror(errno);
+	}
 	mount("proc", "/proc", "proc", MS_NOSUID | MS_NODEV | MS_NOEXEC, NULL);
 	assert_perror(errno);
-	//mount("binfmt_misc", "/proc/sys/fs/binfmt_misc", "binfmt_misc", MS_NOSUID|MS_NODEV|MS_NOEXEC, NULL);
-	//assert_perror(errno);
+	if (args->binfmt) {
+		mount("/tmp", PROC_BINFMT, NULL, MS_MOVE, NULL); 
+		assert_perror(errno);
+	}
 
 	if (args->argc <= 1) {
 		const char *shell = get_shell();
diff --git a/child.h b/child.h
index 18909e4..cb49638 100644
--- a/child.h
+++ b/child.h
@@ -20,6 +20,7 @@
 #ifndef _UROOT_CHILD_H_
 #define _UROOT_CHILD_H_
 
+#include <stdbool.h>
 #include <sys/types.h>
 #include "sigpipe.h"
 
@@ -29,6 +30,7 @@ struct child_args {
 	int argc;
 	char **argv;
 	sigpipe_t sigpipe;
+	bool binfmt;
 };
 
 // Function used as a main for child process
diff --git a/main.c b/main.c
index 0f4815c..058aa3b 100644
--- a/main.c
+++ b/main.c
@@ -41,10 +41,16 @@ static const char doc[] = "Tool using Linux namespaces to provide root like func
 struct opts {
 	char **child_argv;
 	size_t child_argc;
+	bool binfmt;
+};
+
+enum option_key {
+	OPT_BINFMT = 260,
 };
 
 static struct argp_option options[] = {
 	{"debug", 'd', NULL, 0, "Report uroot operations.", 0},
+	{"binfmt", OPT_BINFMT, NULL, 0, "Preserve registered misc binary format handlers.", 0},
 	{NULL}
 };
 
@@ -54,6 +60,9 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
 		case 'd':
 			// TODO logging
 			break;
+		case OPT_BINFMT:
+			opts->binfmt = true;
+			break;
 		case ARGP_KEY_ARGS:
 			opts->child_argc = state->argc - state->next;
 			opts->child_argv = malloc((opts->child_argc + 1) * sizeof *opts->child_argv);
@@ -64,6 +73,7 @@ static error_t parse_opt(int key, char *arg, struct argp_state *state) {
 		case ARGP_KEY_INIT:
 			opts->child_argv = NULL;
 			opts->child_argc = 0;
+			opts->binfmt = false;
 			break;
 		default:
 			return ARGP_ERR_UNKNOWN;
@@ -87,7 +97,8 @@ int main(int argc, char **argv) {
 		.ppid = getpid(),
 		.argc = opts.child_argc,
 		.argv = opts.child_argv,
-		.sigpipe = sigpipe_new()
+		.sigpipe = sigpipe_new(),
+		.binfmt = opts.binfmt,
 	};
 
 	uint8_t stack[STACK_SIZE];
-- 
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