@@ -26,6 +26,10 @@
2626using namespace std;
2727
2828#define err_exit(format, ...) { fprintf(stderr, format ": %s\n", ##__VA_ARGS__, strerror(errno)); exit(EXIT_FAILURE); }
29+static int child_proc(const char *rootdir, const char *nixdir, uint8_t clear_env, list<struct DirMapping> dirMappings, list<struct SetEnv> envMappings, const char *executable, char * const new_argv[]);
30+
31+volatile uint8_t child_died = 0;
32+int child_pid = 0;
2933
3034static void usage(const char *pname) {
3135 fprintf(stderr, "Usage: %s -n <nixpath> -- <command>\n", pname);
@@ -33,6 +37,7 @@ static void usage(const char *pname) {
3337 fprintf(stderr, "\t-m <src>:<src>\tmap src on the host to dest in the sandbox\n");
3438 fprintf(stderr, "\t-d\tdelete all default dir mappings, may break things\n");
3539 fprintf(stderr, "\t-p <var>\tpreserve the value of a variable across the -c clear\n");
40+ fprintf(stderr, "\t-e\tadd an /escape-hatch to the sandbox, and run (outside the sandbox) any strings written to it\n");
3641
3742 exit(EXIT_FAILURE);
3843}
@@ -91,8 +96,15 @@ struct DirMapping parseMapping(string input) {
9196 return (struct DirMapping){ src, dest };
9297}
9398
99+static void handle_child_death(int signo, siginfo_t *info, void *context) {
100+ if ( (child_pid == 0) || (info->si_pid == child_pid) ) {
101+ child_died = 1;
102+ }
103+}
104+
94105int main(int argc, char *argv[]) {
95106 uint8_t clear_env = 0;
107+ uint8_t enable_escape_hatch = 0;
96108 char *nixdir = NULL;
97109 list<struct DirMapping> dirMappings;
98110 list<struct SetEnv> envMappings;
@@ -108,14 +120,18 @@ int main(int argc, char *argv[]) {
108120 x("etc");
109121 x("usr");
110122 x("home");
123+ x("root");
111124#undef x
112125
113126 int opt;
114− while ((opt = getopt(argc, argv, "cn:m:dp:")) != -1) {
127+ while ((opt = getopt(argc, argv, "cen:m:dp:")) != -1) {
115128 switch (opt) {
116129 case 'c':
117130 clear_env = 1;
118131 break;
132+ case 'e':
133+ enable_escape_hatch = 1;
134+ break;
119135 case 'n':
120136 // determine absolute directory for nix dir
121137 nixdir = realpath(optarg, NULL);
@@ -163,6 +179,62 @@ int main(int argc, char *argv[]) {
163179 err_exit("mkdtemp(%s)", template_);
164180 }
165181
182+ int unrace[2];
183+
184+ if (pipe(unrace)) {
185+ err_exit("pipe()");
186+ }
187+
188+ struct sigaction handle_child;
189+ handle_child.sa_sigaction = handle_child_death;
190+ handle_child.sa_flags = SA_SIGINFO;
191+
192+ struct sigaction old_handler;
193+ if (sigaction(SIGCHLD, &handle_child, &old_handler)) {
194+ err_exit("sigaction()");
195+ }
196+
197+ int child;
198+ child = child_pid = fork();
199+ if (child < 0) {
200+ err_exit("fork()");
201+ } else if (child == 0) {
202+ sigaction(SIGCHLD, &old_handler, NULL);
203+ close(unrace[1]);
204+ char buf[10];
205+ read(unrace[0], buf, 10);
206+ close(unrace[0]);
207+ return child_proc(rootdir, nixdir, clear_env, dirMappings, envMappings, argv[optind], argv + optind);
208+ } else {
209+ close(unrace[0]);
210+ char fifopath[PATH_MAX];
211+ if (enable_escape_hatch) {
212+ snprintf(fifopath, PATH_MAX, "%s/escape-hatch", rootdir);
213+ mkfifo(fifopath, 0600);
214+ }
215+ close(unrace[1]);
216+ if (enable_escape_hatch) {
217+ char buffer[1024];
218+ while (!child_died) {
219+ int fd = open(fifopath, O_RDONLY);
220+ if (fd < 0) {
221+ if (errno == EINTR) continue;
222+ fprintf(stderr, "error opening escape-hatch: %s\n", strerror(errno));
223+ continue;
224+ }
225+ int size = read(fd, buffer, 1024);
226+ buffer[size] = 0;
227+ system(buffer);
228+ close(fd);
229+ }
230+ }
231+ int status;
232+ int ret = waitpid(child, &status, 0);
233+ return WEXITSTATUS(status);
234+ }
235+}
236+
237+static int child_proc(const char *rootdir, const char *nixdir, uint8_t clear_env, list<struct DirMapping> dirMappings, list<struct SetEnv> envMappings, const char *executable, char * const new_argv[]) {
166238 // get uid, gid before going to new namespace
167239 uid_t uid = getuid();
168240 gid_t gid = getgid();
@@ -170,7 +242,7 @@ int main(int argc, char *argv[]) {
170242 // "unshare" into new namespace
171243 if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) {
172244 if (errno == EPERM) {
173− fputs("Run the following as root to enable unprivileged namespace use:\nsysctl -w kernel.unprivileged_userns_clone=1 ; echo kernel.unprivileged_userns_clone=1 > /etc/sysctl.d/nix-user-chroot.conf\n\n", stderr);
245+ fputs("Run the following to enable unprivileged namespace use:\nsudo bash -c \"sysctl -w kernel.unprivileged_userns_clone=1 ; echo kernel.unprivileged_userns_clone=1 > /etc/sysctl.d/nix-user-chroot.conf\"\n\n", stderr);
174246 exit(EXIT_FAILURE);
175247 } else {
176248 err_exit("unshare()");
@@ -230,6 +302,6 @@ int main(int argc, char *argv[]) {
230302 }
231303
232304 // execute the command
233− execvp(argv[optind], argv + optind);
234− err_exit("execvp(%s)", argv[optind]);
305+ execvp(executable, new_argv);
306+ err_exit("execvp(%s)", executable);
235307}