int lxc_attach(const char* name, const char* lxcpath, lxc_attach_exec_t exec_function, void* exec_payload, lxc_attach_options_t* options, pid_t* attached_process)
{
int ret, status;
pid_t init_pid, pid, attached_pid, expected;
struct lxc_proc_context_info *init_ctx;
char* cwd;
char* new_cwd;
int ipc_sockets[2];
signed long personality;
if (!options)
options = &attach_static_default_options;
init_pid = lxc_cmd_get_init_pid(name, lxcpath);
if (init_pid < 0) {
ERROR("Failed to get init pid.");
return -1;
}
init_ctx = lxc_proc_get_context_info(init_pid);
if (!init_ctx) {
ERROR("Failed to get context of init process: %ld.",
(long)init_pid);
return -1;
}
personality = get_personality(name, lxcpath);
if (init_ctx->personality < 0) {
ERROR("Failed to get personality of the container.");
lxc_proc_put_context_info(init_ctx);
return -1;
}
init_ctx->personality = personality;
init_ctx->container = lxc_container_new(name, lxcpath);
if (!init_ctx->container)
return -1;
if (!fetch_seccomp(init_ctx->container, options))
WARN("Failed to get seccomp policy.");
if (!no_new_privs(init_ctx->container, options))
WARN("Could not determine whether PR_SET_NO_NEW_PRIVS is set.");
cwd = getcwd(NULL, 0);
/* Determine which namespaces the container was created with
* by asking lxc-start, if necessary.
*/
if (options->namespaces == -1) {
options->namespaces = lxc_cmd_get_clone_flags(name, lxcpath);
/* call failed */
if (options->namespaces == -1) {
ERROR("Failed to automatically determine the "
"namespaces which the container uses.");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
}
/* Create a socket pair for IPC communication; set SOCK_CLOEXEC in order
* to make sure we don't irritate other threads that want to fork+exec
* away
*
* IMPORTANT: if the initial process is multithreaded and another call
* just fork()s away without exec'ing directly after, the socket fd will
* exist in the forked process from the other thread and any close() in
* our own child process will not really cause the socket to close
* properly, potentiall causing the parent to hang.
*
* For this reason, while IPC is still active, we have to use shutdown()
* if the child exits prematurely in order to signal that the socket is
* closed and cannot assume that the child exiting will automatically do
* that.
*
* IPC mechanism: (X is receiver)
* initial process intermediate attached
* X <--- send pid of
* attached proc,
* then exit
* send 0 ------------------------------------> X
* [do initialization]
* X <------------------------------------ send 1
* [add to cgroup, ...]
* send 2 ------------------------------------> X
* [set LXC_ATTACH_NO_NEW_PRIVS]
* X <------------------------------------ send 3
* [open LSM label fd]
* send 4 ------------------------------------> X
* [set LSM label]
* close socket close socket
* run program
*/
ret = socketpair(PF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, ipc_sockets);
if (ret < 0) {
SYSERROR("Could not set up required IPC mechanism for attaching.");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
/* Create intermediate subprocess, three reasons:
* 1. Runs all pthread_atfork handlers and the child will no
* longer be threaded (we can't properly setns() in a threaded
* process).
* 2. We can't setns() in the child itself, since we want to make
* sure we are properly attached to the pidns.
* 3. Also, the initial thread has to put the attached process
* into the cgroup, which we can only do if we didn't already
* setns() (otherwise, user namespaces will hate us).
*/
pid = fork();
if (pid < 0) {
SYSERROR("Failed to create first subprocess.");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
if (pid) {
int procfd = -1;
pid_t to_cleanup_pid = pid;
/* Initial thread, we close the socket that is for the
* subprocesses.
*/
close(ipc_sockets[1]);
free(cwd);
/* Attach to cgroup, if requested. */
if (options->attach_flags & LXC_ATTACH_MOVE_TO_CGROUP) {
if (!cgroup_attach(name, lxcpath, pid))
goto on_error;
}
/* Setup resource limits */
if (!lxc_list_empty(&init_ctx->container->lxc_conf->limits) && setup_resource_limits(&init_ctx->container->lxc_conf->limits, pid)) {
goto on_error;
}
/* Open /proc before setns() to the containers namespace so we
* don't rely on any information from inside the container.
*/
procfd = open("/proc", O_DIRECTORY | O_RDONLY | O_CLOEXEC);
if (procfd < 0) {
SYSERROR("Unable to open /proc.");
goto on_error;
}
/* Let the child process know to go ahead. */
status = 0;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("Intended to send sequence number 0: %s.",
strerror(errno));
goto on_error;
}
/* Get pid of attached process from intermediate process. */
ret = lxc_read_nointr_expect(ipc_sockets[0], &attached_pid, sizeof(attached_pid), NULL);
if (ret <= 0) {
if (ret != 0)
ERROR("Expected to receive pid: %s.", strerror(errno));
goto on_error;
}
/* Ignore SIGKILL (CTRL-C) and SIGQUIT (CTRL-\) - issue #313. */
if (options->stdin_fd == 0) {
signal(SIGINT, SIG_IGN);
signal(SIGQUIT, SIG_IGN);
}
/* Reap intermediate process. */
ret = wait_for_pid(pid);
if (ret < 0)
goto on_error;
/* We will always have to reap the attached process now. */
to_cleanup_pid = attached_pid;
/* Tell attached process it may start initializing. */
status = 0;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("Intended to send sequence number 0: %s.", strerror(errno));
goto on_error;
}
/* Wait for the attached process to finish initializing. */
expected = 1;
ret = lxc_read_nointr_expect(ipc_sockets[0], &status, sizeof(status), &expected);
if (ret <= 0) {
if (ret != 0)
ERROR("Expected to receive sequence number 1: %s.", strerror(errno));
goto on_error;
}
/* Tell attached process we're done. */
status = 2;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("Intended to send sequence number 2: %s.", strerror(errno));
goto on_error;
}
/* Wait for the (grand)child to tell us that it's ready to set
* up its LSM labels.
*/
expected = 3;
ret = lxc_read_nointr_expect(ipc_sockets[0], &status, sizeof(status), &expected);
if (ret <= 0) {
ERROR("Expected to receive sequence number 3: %s.",
strerror(errno));
goto on_error;
}
/* Open LSM fd and send it to child. */
if ((options->namespaces & CLONE_NEWNS) && (options->attach_flags & LXC_ATTACH_LSM) && init_ctx->lsm_label) {
int on_exec, saved_errno;
int labelfd = -1;
on_exec = options->attach_flags & LXC_ATTACH_LSM_EXEC ? 1 : 0;
/* Open fd for the LSM security module. */
labelfd = lsm_openat(procfd, attached_pid, on_exec);
if (labelfd < 0)
goto on_error;
/* Send child fd of the LSM security module to write to. */
ret = lxc_abstract_unix_send_fds(ipc_sockets[0], &labelfd, 1, NULL, 0);
saved_errno = errno;
close(labelfd);
if (ret <= 0) {
ERROR("Intended to send file descriptor %d: %s.", labelfd, strerror(saved_errno));
goto on_error;
}
}
if (procfd >= 0)
close(procfd);
/* Now shut down communication with child, we're done. */
shutdown(ipc_sockets[0], SHUT_RDWR);
close(ipc_sockets[0]);
lxc_proc_put_context_info(init_ctx);
/* We're done, the child process should now execute whatever it
* is that the user requested. The parent can now track it with
* waitpid() or similar.
*/
*attached_process = attached_pid;
return 0;
on_error:
/* First shut down the socket, then wait for the pid, otherwise
* the pid we're waiting for may never exit.
*/
if (procfd >= 0)
close(procfd);
shutdown(ipc_sockets[0], SHUT_RDWR);
close(ipc_sockets[0]);
if (to_cleanup_pid)
(void) wait_for_pid(to_cleanup_pid);
lxc_proc_put_context_info(init_ctx);
return -1;
}
/* First subprocess begins here, we close the socket that is for the
* initial thread.
*/
close(ipc_sockets[0]);
/* Wait for the parent to have setup cgroups. */
expected = 0;
status = -1;
ret = lxc_read_nointr_expect(ipc_sockets[1], &status, sizeof(status), &expected);
if (ret <= 0) {
ERROR("Expected to receive sequence number 0: %s.", strerror(errno));
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
if ((options->attach_flags & LXC_ATTACH_MOVE_TO_CGROUP) && cgns_supported())
options->namespaces |= CLONE_NEWCGROUP;
/* Attach now, create another subprocess later, since pid namespaces
* only really affect the children of the current process.
*/
ret = lxc_attach_to_ns(init_pid, options->namespaces);
if (ret < 0) {
ERROR("Failed to enter namespaces.");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* Attach succeeded, try to cwd. */
if (options->initial_cwd)
new_cwd = options->initial_cwd;
else
new_cwd = cwd;
ret = chdir(new_cwd);
if (ret < 0)
WARN("Could not change directory to \"%s\".", new_cwd);
free(cwd);
/* Now create the real child process. */
{
struct attach_clone_payload payload = {
.ipc_socket = ipc_sockets[1],
.options = options,
.init_ctx = init_ctx,
.exec_function = exec_function,
.exec_payload = exec_payload,
};
/* We use clone_parent here to make this subprocess a direct
* child of the initial process. Then this intermediate process
* can exit and the parent can directly track the attached
* process.
*/
pid = lxc_clone(attach_child_main, &payload, CLONE_PARENT);
}
/* Shouldn't happen, clone() should always return positive pid. */
if (pid <= 0) {
SYSERROR("Failed to create subprocess.");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* Tell grandparent the pid of the pid of the newly created child. */
ret = lxc_write_nointr(ipc_sockets[1], &pid, sizeof(pid));
if (ret != sizeof(pid)) {
/* If this really happens here, this is very unfortunate, since
* the parent will not know the pid of the attached process and
* will not be able to wait for it (and we won't either due to
* CLONE_PARENT) so the parent won't be able to reap it and the
* attached process will remain a zombie.
*/
ERROR("Intended to send pid %d: %s.", pid, strerror(errno));
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* The rest is in the hands of the initial and the attached process. */
rexit(0);
}
int lxc_attach(const char* name, const char* lxcpath, lxc_attach_exec_t exec_function, void* exec_payload, lxc_attach_options_t* options, pid_t* attached_process)
{
int ret, status;
pid_t init_pid, pid, attached_pid, expected;
struct lxc_proc_context_info *init_ctx;
char* cwd;
char* new_cwd;
int ipc_sockets[2];
int procfd;
signed long personality;
if (!options)
options = &attach_static_default_options;
init_pid = lxc_cmd_get_init_pid(name, lxcpath);
if (init_pid < 0) {
ERROR("failed to get the init pid");
return -1;
}
init_ctx = lxc_proc_get_context_info(init_pid);
if (!init_ctx) {
ERROR("failed to get context of the init process, pid = %ld", (long)init_pid);
return -1;
}
personality = get_personality(name, lxcpath);
if (init_ctx->personality < 0) {
ERROR("Failed to get personality of the container");
lxc_proc_put_context_info(init_ctx);
return -1;
}
init_ctx->personality = personality;
if (!fetch_seccomp(name, lxcpath, init_ctx, options))
WARN("Failed to get seccomp policy");
cwd = getcwd(NULL, 0);
/* determine which namespaces the container was created with
* by asking lxc-start, if necessary
*/
if (options->namespaces == -1) {
options->namespaces = lxc_cmd_get_clone_flags(name, lxcpath);
/* call failed */
if (options->namespaces == -1) {
ERROR("failed to automatically determine the "
"namespaces which the container unshared");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
}
/* create a socket pair for IPC communication; set SOCK_CLOEXEC in order
* to make sure we don't irritate other threads that want to fork+exec away
*
* IMPORTANT: if the initial process is multithreaded and another call
* just fork()s away without exec'ing directly after, the socket fd will
* exist in the forked process from the other thread and any close() in
* our own child process will not really cause the socket to close properly,
* potentiall causing the parent to hang.
*
* For this reason, while IPC is still active, we have to use shutdown()
* if the child exits prematurely in order to signal that the socket
* is closed and cannot assume that the child exiting will automatically
* do that.
*
* IPC mechanism: (X is receiver)
* initial process intermediate attached
* X <--- send pid of
* attached proc,
* then exit
* send 0 ------------------------------------> X
* [do initialization]
* X <------------------------------------ send 1
* [add to cgroup, ...]
* send 2 ------------------------------------> X
* close socket close socket
* run program
*/
ret = socketpair(PF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0, ipc_sockets);
if (ret < 0) {
SYSERROR("could not set up required IPC mechanism for attaching");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
/* create intermediate subprocess, three reasons:
* 1. runs all pthread_atfork handlers and the
* child will no longer be threaded
* (we can't properly setns() in a threaded process)
* 2. we can't setns() in the child itself, since
* we want to make sure we are properly attached to
* the pidns
* 3. also, the initial thread has to put the attached
* process into the cgroup, which we can only do if
* we didn't already setns() (otherwise, user
* namespaces will hate us)
*/
pid = fork();
if (pid < 0) {
SYSERROR("failed to create first subprocess");
free(cwd);
lxc_proc_put_context_info(init_ctx);
return -1;
}
if (pid) {
pid_t to_cleanup_pid = pid;
/* initial thread, we close the socket that is for the
* subprocesses
*/
close(ipc_sockets[1]);
free(cwd);
/* attach to cgroup, if requested */
if (options->attach_flags & LXC_ATTACH_MOVE_TO_CGROUP) {
if (!cgroup_attach(name, lxcpath, pid))
goto cleanup_error;
}
/* Let the child process know to go ahead */
status = 0;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("error using IPC to notify attached process for initialization (0)");
goto cleanup_error;
}
/* get pid from intermediate process */
ret = lxc_read_nointr_expect(ipc_sockets[0], &attached_pid, sizeof(attached_pid), NULL);
if (ret <= 0) {
if (ret != 0)
ERROR("error using IPC to receive pid of attached process");
goto cleanup_error;
}
/* ignore SIGKILL (CTRL-C) and SIGQUIT (CTRL-\) - issue #313 */
if (options->stdin_fd == 0) {
signal(SIGINT, SIG_IGN);
signal(SIGQUIT, SIG_IGN);
}
/* reap intermediate process */
ret = wait_for_pid(pid);
if (ret < 0)
goto cleanup_error;
/* we will always have to reap the grandchild now */
to_cleanup_pid = attached_pid;
/* tell attached process it may start initializing */
status = 0;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("error using IPC to notify attached process for initialization (0)");
goto cleanup_error;
}
/* wait for the attached process to finish initializing */
expected = 1;
ret = lxc_read_nointr_expect(ipc_sockets[0], &status, sizeof(status), &expected);
if (ret <= 0) {
if (ret != 0)
ERROR("error using IPC to receive notification from attached process (1)");
goto cleanup_error;
}
/* tell attached process we're done */
status = 2;
ret = lxc_write_nointr(ipc_sockets[0], &status, sizeof(status));
if (ret <= 0) {
ERROR("error using IPC to notify attached process for initialization (2)");
goto cleanup_error;
}
/* now shut down communication with child, we're done */
shutdown(ipc_sockets[0], SHUT_RDWR);
close(ipc_sockets[0]);
lxc_proc_put_context_info(init_ctx);
/* we're done, the child process should now execute whatever
* it is that the user requested. The parent can now track it
* with waitpid() or similar.
*/
*attached_process = attached_pid;
return 0;
cleanup_error:
/* first shut down the socket, then wait for the pid,
* otherwise the pid we're waiting for may never exit
*/
shutdown(ipc_sockets[0], SHUT_RDWR);
close(ipc_sockets[0]);
if (to_cleanup_pid)
(void) wait_for_pid(to_cleanup_pid);
lxc_proc_put_context_info(init_ctx);
return -1;
}
/* first subprocess begins here, we close the socket that is for the
* initial thread
*/
close(ipc_sockets[0]);
/* Wait for the parent to have setup cgroups */
expected = 0;
status = -1;
ret = lxc_read_nointr_expect(ipc_sockets[1], &status, sizeof(status), &expected);
if (ret <= 0) {
ERROR("error communicating with child process");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
if ((options->attach_flags & LXC_ATTACH_MOVE_TO_CGROUP) && cgns_supported())
options->namespaces |= CLONE_NEWCGROUP;
procfd = open("/proc", O_DIRECTORY | O_RDONLY);
if (procfd < 0) {
SYSERROR("Unable to open /proc");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* attach now, create another subprocess later, since pid namespaces
* only really affect the children of the current process
*/
ret = lxc_attach_to_ns(init_pid, options->namespaces);
if (ret < 0) {
ERROR("failed to enter the namespace");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* attach succeeded, try to cwd */
if (options->initial_cwd)
new_cwd = options->initial_cwd;
else
new_cwd = cwd;
ret = chdir(new_cwd);
if (ret < 0)
WARN("could not change directory to '%s'", new_cwd);
free(cwd);
/* now create the real child process */
{
struct attach_clone_payload payload = {
.ipc_socket = ipc_sockets[1],
.options = options,
.init_ctx = init_ctx,
.exec_function = exec_function,
.exec_payload = exec_payload,
.procfd = procfd
};
/* We use clone_parent here to make this subprocess a direct child of
* the initial process. Then this intermediate process can exit and
* the parent can directly track the attached process.
*/
pid = lxc_clone(attach_child_main, &payload, CLONE_PARENT);
}
/* shouldn't happen, clone() should always return positive pid */
if (pid <= 0) {
SYSERROR("failed to create subprocess");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* tell grandparent the pid of the pid of the newly created child */
ret = lxc_write_nointr(ipc_sockets[1], &pid, sizeof(pid));
if (ret != sizeof(pid)) {
/* if this really happens here, this is very unfortunate, since the
* parent will not know the pid of the attached process and will
* not be able to wait for it (and we won't either due to CLONE_PARENT)
* so the parent won't be able to reap it and the attached process
* will remain a zombie
*/
ERROR("error using IPC to notify main process of pid of the attached process");
shutdown(ipc_sockets[1], SHUT_RDWR);
rexit(-1);
}
/* the rest is in the hands of the initial and the attached process */
rexit(0);
}