terminal: safely allocate pts devices from inside the container

This was a year long journey which seems to finally have come to an end.

Closes: #1620.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Christian Brauner 2020-08-05 12:03:41 +02:00
parent f3bbb01f8a
commit f797f05e6e
No known key found for this signature in database
GPG Key ID: 8EB056D53EECB12D
12 changed files with 158 additions and 8 deletions

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@ -131,3 +131,8 @@ This adds time namespace support to LXC.
## seccomp\_allow\_deny\_syntax
This adds the ability to use "denylist" and "allowlist" in seccomp v2 policies.
## devpts\_fd
This adds the ability to allocate a file descriptor for the devpts instance of
the container.

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@ -43,6 +43,7 @@ static char *api_extensions[] = {
"network_bridge_vlan",
"time_namespace",
"seccomp_allow_deny_syntax",
"devpts_fd",
};
static size_t nr_api_extensions = sizeof(api_extensions) / sizeof(*api_extensions);

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@ -889,14 +889,14 @@ on_error:
_exit(EXIT_FAILURE);
}
static int lxc_attach_terminal(struct lxc_conf *conf,
static int lxc_attach_terminal(const char *name, const char *lxcpath, struct lxc_conf *conf,
struct lxc_terminal *terminal)
{
int ret;
lxc_terminal_init(terminal);
ret = lxc_terminal_create(terminal);
ret = lxc_terminal_create(name, lxcpath, terminal);
if (ret < 0)
return log_error(-1, "Failed to create terminal");
@ -1091,7 +1091,7 @@ int lxc_attach(struct lxc_container *container, lxc_attach_exec_t exec_function,
}
if (options->attach_flags & LXC_ATTACH_TERMINAL) {
ret = lxc_attach_terminal(conf, &terminal);
ret = lxc_attach_terminal(name, lxcpath, conf, &terminal);
if (ret < 0) {
ERROR("Failed to setup new terminal");
free(cwd);

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@ -86,6 +86,7 @@ static const char *lxc_cmd_str(lxc_cmd_t cmd)
[LXC_CMD_GET_INIT_PIDFD] = "get_init_pidfd",
[LXC_CMD_GET_LIMITING_CGROUP] = "get_limiting_cgroup",
[LXC_CMD_GET_LIMITING_CGROUP2_FD] = "get_limiting_cgroup2_fd",
[LXC_CMD_GET_DEVPTS_FD] = "get_devpts_fd",
};
if (cmd >= LXC_CMD_MAX)
@ -156,6 +157,11 @@ static int lxc_cmd_rsp_recv(int sock, struct lxc_cmd_rr *cmd)
rsp->data = INT_TO_PTR(init_pidfd);
}
if (cmd->req.cmd == LXC_CMD_GET_DEVPTS_FD) {
int devpts_fd = move_fd(fd_rsp);
rsp->data = INT_TO_PTR(devpts_fd);
}
if (rsp->datalen == 0)
return log_debug(ret,
"Response data length for command \"%s\" is 0",
@ -447,6 +453,43 @@ static int lxc_cmd_get_init_pidfd_callback(int fd, struct lxc_cmd_req *req,
return 0;
}
int lxc_cmd_get_devpts_fd(const char *name, const char *lxcpath)
{
int ret, stopped;
struct lxc_cmd_rr cmd = {
.req = {
.cmd = LXC_CMD_GET_DEVPTS_FD,
},
};
ret = lxc_cmd(name, &cmd, &stopped, lxcpath, NULL);
if (ret < 0)
return log_debug_errno(-1, errno, "Failed to process devpts fd command");
if (cmd.rsp.ret < 0)
return log_debug_errno(-EBADF, errno, "Failed to receive devpts fd");
return PTR_TO_INT(cmd.rsp.data);
}
static int lxc_cmd_get_devpts_fd_callback(int fd, struct lxc_cmd_req *req,
struct lxc_handler *handler,
struct lxc_epoll_descr *descr)
{
struct lxc_cmd_rsp rsp = {
.ret = 0,
};
int ret;
if (!handler->conf || handler->conf->devpts_fd < 0)
rsp.ret = -EBADF;
ret = lxc_abstract_unix_send_fds(fd, &handler->conf->devpts_fd, 1, &rsp, sizeof(rsp));
if (ret < 0)
return log_error(LXC_CMD_REAP_CLIENT_FD, "Failed to send devpts fd");
return 0;
}
/*
* lxc_cmd_get_clone_flags: Get clone flags container was spawned with
*
@ -1505,6 +1548,7 @@ static int lxc_cmd_process(int fd, struct lxc_cmd_req *req,
[LXC_CMD_GET_INIT_PIDFD] = lxc_cmd_get_init_pidfd_callback,
[LXC_CMD_GET_LIMITING_CGROUP] = lxc_cmd_get_limiting_cgroup_callback,
[LXC_CMD_GET_LIMITING_CGROUP2_FD] = lxc_cmd_get_limiting_cgroup2_fd_callback,
[LXC_CMD_GET_DEVPTS_FD] = lxc_cmd_get_devpts_fd_callback,
};
if (req->cmd >= LXC_CMD_MAX)

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@ -41,6 +41,7 @@ typedef enum {
LXC_CMD_GET_INIT_PIDFD,
LXC_CMD_GET_LIMITING_CGROUP,
LXC_CMD_GET_LIMITING_CGROUP2_FD,
LXC_CMD_GET_DEVPTS_FD,
LXC_CMD_MAX,
} lxc_cmd_t;
@ -132,5 +133,6 @@ __hidden extern int lxc_cmd_get_cgroup2_fd(const char *name, const char *lxcpath
__hidden extern char *lxc_cmd_get_limiting_cgroup_path(const char *name, const char *lxcpath,
const char *subsystem);
__hidden extern int lxc_cmd_get_limiting_cgroup2_fd(const char *name, const char *lxcpath);
__hidden extern int lxc_cmd_get_devpts_fd(const char *name, const char *lxcpath);
#endif /* __commands_h */

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@ -1472,13 +1472,16 @@ static const struct id_map *find_mapped_nsid_entry(const struct lxc_conf *conf,
return retmap;
}
static int lxc_setup_devpts(struct lxc_conf *conf)
static int lxc_setup_devpts(struct lxc_handler *handler)
{
__do_close int devpts_fd = -EBADF;
int ret;
char **opts;
char devpts_mntopts[256];
char *mntopt_sets[5];
char default_devpts_mntopts[256] = "gid=5,newinstance,ptmxmode=0666,mode=0620";
struct lxc_conf *conf = handler->conf;
int sock = handler->data_sock[0];
if (conf->pty_max <= 0)
return log_debug(0, "No new devpts instance will be mounted since no pts devices are requested");
@ -1521,6 +1524,16 @@ static int lxc_setup_devpts(struct lxc_conf *conf)
return log_error_errno(-1, errno, "Failed to mount new devpts instance");
DEBUG("Mount new devpts instance with options \"%s\"", *opts);
devpts_fd = open_tree(-EBADF, "/dev/pts", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC | AT_EMPTY_PATH);
if (devpts_fd < 0) {
TRACE("Failed to create detached devpts mount");
ret = lxc_abstract_unix_send_fds(sock, NULL, 0, NULL, 0);
} else {
ret = lxc_abstract_unix_send_fds(sock, &devpts_fd, 1, NULL, 0);
}
if (ret < 0)
return log_error_errno(-1, errno, "Failed to send devpts fd to parent");
/* Remove any pre-existing /dev/ptmx file. */
ret = remove("/dev/ptmx");
if (ret < 0) {
@ -3327,7 +3340,7 @@ int lxc_setup(struct lxc_handler *handler)
if (lxc_conf->autodev > 0)
(void)lxc_setup_boot_id();
ret = lxc_setup_devpts(lxc_conf);
ret = lxc_setup_devpts(handler);
if (ret < 0)
return log_error(-1, "Failed to setup new devpts instance");

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@ -292,6 +292,8 @@ struct lxc_conf {
struct lxc_terminal console;
/* maximum pty devices allowed by devpts mount */
size_t pty_max;
/* file descriptor for the container's /dev/pts mount */
int devpts_fd;
/* set to true when rootfs has been setup */
bool rootfs_setup;

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@ -608,6 +608,16 @@ static int do_lxcapi_init_pidfd(struct lxc_container *c)
WRAP_API(int, lxcapi_init_pidfd)
static int do_lxcapi_devpts_fd(struct lxc_container *c)
{
if (!c)
return ret_errno(EBADF);
return lxc_cmd_get_devpts_fd(c->name, c->config_path);
}
WRAP_API(int, lxcapi_devpts_fd)
static bool load_config_locked(struct lxc_container *c, const char *fname)
{
if (!c->lxc_conf)
@ -5319,6 +5329,7 @@ struct lxc_container *lxc_container_new(const char *name, const char *configpath
c->unfreeze = lxcapi_unfreeze;
c->console = lxcapi_console;
c->console_getfd = lxcapi_console_getfd;
c->devpts_fd = lxcapi_devpts_fd;
c->init_pid = lxcapi_init_pid;
c->init_pidfd = lxcapi_init_pidfd;
c->load_config = lxcapi_load_config;

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@ -865,6 +865,15 @@ struct lxc_container {
* \return pidfd of init process of the container.
*/
int (*init_pidfd)(struct lxc_container *c);
/*!
* \brief Retrieve a mount fd for the container's devpts instance.
*
* \param c Container.
*
* \return Mount fd of the container's devpts instance.
*/
int (*devpts_fd)(struct lxc_container *c);
};
/*!

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@ -980,6 +980,7 @@ void lxc_end(struct lxc_handler *handler)
lxc_terminal_delete(&handler->conf->console);
lxc_delete_tty(&handler->conf->ttys);
close_prot_errno_disarm(handler->conf->devpts_fd);
/* The command socket is now closed, no more state clients can register
* themselves from now on. So free the list of state clients.
@ -1959,6 +1960,14 @@ static int lxc_spawn(struct lxc_handler *handler)
}
}
ret = lxc_abstract_unix_recv_fds(data_sock1, &handler->conf->devpts_fd, 1, NULL, 0);
if (ret < 0) {
SYSERROR("Failed to receive devpts fd from child");
goto out_delete_net;
}
if (ret == 0)
handler->conf->devpts_fd = -EBADF;
/* Now all networks are created, network devices are moved into place,
* and the correct names and ifindices in the respective namespaces have
* been recorded. The corresponding structs have now all been filled. So

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@ -828,7 +828,7 @@ int lxc_terminal_create_log_file(struct lxc_terminal *terminal)
return 0;
}
int lxc_terminal_create(struct lxc_terminal *terminal)
static int lxc_terminal_create_foreign(struct lxc_terminal *terminal)
{
int ret;
@ -869,6 +869,59 @@ err:
return -ENODEV;
}
static int lxc_terminal_create_native(const char *name, const char *lxcpath,
struct lxc_terminal *terminal)
{
__do_close int devpts_fd = -EBADF, ptx_fd = -EBADF, pty_fd = -EBADF;
int ret;
devpts_fd = lxc_cmd_get_devpts_fd(name, lxcpath);
if (devpts_fd < 0)
return log_error_errno(-1, errno, "Failed to receive devpts fd");
ptx_fd = openat(devpts_fd, "ptmx", O_RDWR | O_NOCTTY | O_CLOEXEC);
if (ptx_fd < 0)
return log_error_errno(-1, errno, "Failed to open terminal multiplexer device");
ret = grantpt(ptx_fd);
if (ret < 0)
return log_error_errno(-1, errno, "Failed to grant access to multiplexer device");
ret = unlockpt(ptx_fd);
if (ret < 0)
return log_error_errno(-1, errno, "Failed to unlock multiplexer device device");
pty_fd = ioctl(ptx_fd, TIOCGPTPEER, O_RDWR | O_NOCTTY | O_CLOEXEC);
if (pty_fd < 0)
return log_error_errno(-1, errno, "Failed to allocate new pty device");
ret = ttyname_r(terminal->pty, terminal->name, sizeof(terminal->name));
if (ret < 0)
return log_error_errno(-1, errno, "Failed to retrieve name of terminal pty");
terminal->ptx = move_fd(ptx_fd);
terminal->pty = move_fd(pty_fd);
ret = lxc_terminal_peer_default(terminal);
if (ret < 0) {
ERROR("Failed to allocate proxy terminal");
goto err;
}
return 0;
err:
lxc_terminal_delete(terminal);
return -ENODEV;
}
int lxc_terminal_create(const char *name, const char *lxcpath, struct lxc_terminal *terminal)
{
if (!lxc_terminal_create_native(name, lxcpath, terminal))
return 0;
return lxc_terminal_create_foreign(terminal);
}
int lxc_terminal_setup(struct lxc_conf *conf)
{
int ret;
@ -879,7 +932,7 @@ int lxc_terminal_setup(struct lxc_conf *conf)
return 0;
}
ret = lxc_terminal_create(terminal);
ret = lxc_terminal_create_foreign(terminal);
if (ret < 0)
return -1;

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@ -110,7 +110,8 @@ __hidden extern int lxc_terminal_allocate(struct lxc_conf *conf, int sockfd, in
* - sets up SIGWINCH handler, winsz, and new terminal settings
* (Handlers for SIGWINCH and I/O are not registered in a mainloop.)
*/
__hidden extern int lxc_terminal_create(struct lxc_terminal *console);
__hidden extern int lxc_terminal_create(const char *name, const char *lxcpath,
struct lxc_terminal *console);
/**
* lxc_terminal_setup: Create a new terminal.