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Merge pull request #41 from input-output-hk/escape-hatch

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add an escape-hatch option to allow things like xdg-open to work inside the sandbox
This commit is contained in:
Matthew Bauer 2018-10-21 19:41:26 -05:00 committed by GitHub
commit 113d8c6b42
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 75 additions and 4 deletions
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79
nix-user-chroot/main.cpp
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@ -26,6 +26,10 @@
using namespace std;
#define err_exit(format, ...) { fprintf(stderr, format ": %s\n", ##__VA_ARGS__, strerror(errno)); exit(EXIT_FAILURE); }
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[]);
volatile uint8_t child_died = 0;
int child_pid = 0;
static void usage(const char *pname) {
fprintf(stderr, "Usage: %s -n <nixpath> -- <command>\n", pname);
@ -33,6 +37,7 @@ static void usage(const char *pname) {
fprintf(stderr, "\t-m <src>:<src>\tmap src on the host to dest in the sandbox\n");
fprintf(stderr, "\t-d\tdelete all default dir mappings, may break things\n");
fprintf(stderr, "\t-p <var>\tpreserve the value of a variable across the -c clear\n");
fprintf(stderr, "\t-e\tadd an /escape-hatch to the sandbox, and run (outside the sandbox) any strings written to it\n");
exit(EXIT_FAILURE);
}
@ -91,8 +96,15 @@ struct DirMapping parseMapping(string input) {
return (struct DirMapping){ src, dest };
}
static void handle_child_death(int signo, siginfo_t *info, void *context) {
if ( (child_pid == 0) || (info->si_pid == child_pid) ) {
child_died = 1;
}
}
int main(int argc, char *argv[]) {
uint8_t clear_env = 0;
uint8_t enable_escape_hatch = 0;
char *nixdir = NULL;
list<struct DirMapping> dirMappings;
list<struct SetEnv> envMappings;
@ -111,11 +123,14 @@ int main(int argc, char *argv[]) {
#undef x
int opt;
while ((opt = getopt(argc, argv, "cn:m:dp:")) != -1) {
while ((opt = getopt(argc, argv, "cen:m:dp:")) != -1) {
switch (opt) {
case 'c':
clear_env = 1;
break;
case 'e':
enable_escape_hatch = 1;
break;
case 'n':
// determine absolute directory for nix dir
nixdir = realpath(optarg, NULL);
@ -163,6 +178,62 @@ int main(int argc, char *argv[]) {
err_exit("mkdtemp(%s)", template_);
}
int unrace[2];
if (pipe(unrace)) {
err_exit("pipe()");
}
struct sigaction handle_child;
handle_child.sa_sigaction = handle_child_death;
handle_child.sa_flags = SA_SIGINFO;
struct sigaction old_handler;
if (sigaction(SIGCHLD, &handle_child, &old_handler)) {
err_exit("sigaction()");
}
int child;
child = child_pid = fork();
if (child < 0) {
err_exit("fork()");
} else if (child == 0) {
sigaction(SIGCHLD, &old_handler, NULL);
close(unrace[1]);
char buf[10];
read(unrace[0], buf, 10);
close(unrace[0]);
return child_proc(rootdir, nixdir, clear_env, dirMappings, envMappings, argv[optind], argv + optind);
} else {
close(unrace[0]);
char fifopath[PATH_MAX];
if (enable_escape_hatch) {
snprintf(fifopath, PATH_MAX, "%s/escape-hatch", rootdir);
mkfifo(fifopath, 0600);
}
close(unrace[1]);
if (enable_escape_hatch) {
char buffer[1024];
while (!child_died) {
int fd = open(fifopath, O_RDONLY);
if (fd < 0) {
if (errno == EINTR) continue;
fprintf(stderr, "error opening escape-hatch: %s\n", strerror(errno));
continue;
}
int size = read(fd, buffer, 1024);
buffer[size] = 0;
system(buffer);
close(fd);
}
}
int status;
int ret = waitpid(child, &status, 0);
return WEXITSTATUS(status);
}
}
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[]) {
// get uid, gid before going to new namespace
uid_t uid = getuid();
gid_t gid = getgid();
@ -170,7 +241,7 @@ int main(int argc, char *argv[]) {
// "unshare" into new namespace
if (unshare(CLONE_NEWNS | CLONE_NEWUSER) < 0) {
if (errno == EPERM) {
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);
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);
exit(EXIT_FAILURE);
} else {
err_exit("unshare()");
@ -230,6 +301,6 @@ int main(int argc, char *argv[]) {
}
// execute the command
execvp(argv[optind], argv + optind);
err_exit("execvp(%s)", argv[optind]);
execvp(executable, new_argv);
err_exit("execvp(%s)", executable);
}