diff options
Diffstat (limited to 'src/basic/namespace-util.c')
| -rw-r--r-- | src/basic/namespace-util.c | 262 |
1 files changed, 262 insertions, 0 deletions
diff --git a/src/basic/namespace-util.c b/src/basic/namespace-util.c new file mode 100644 index 0000000..a87a875 --- /dev/null +++ b/src/basic/namespace-util.c @@ -0,0 +1,262 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <fcntl.h> +#include <sys/ioctl.h> +#include <sys/mount.h> + +#include "errno-util.h" +#include "fd-util.h" +#include "fileio.h" +#include "missing_fs.h" +#include "missing_magic.h" +#include "missing_sched.h" +#include "namespace-util.h" +#include "process-util.h" +#include "stat-util.h" +#include "stdio-util.h" +#include "user-util.h" + +const struct namespace_info namespace_info[] = { + [NAMESPACE_CGROUP] = { "cgroup", "ns/cgroup", CLONE_NEWCGROUP, }, + [NAMESPACE_IPC] = { "ipc", "ns/ipc", CLONE_NEWIPC, }, + [NAMESPACE_NET] = { "net", "ns/net", CLONE_NEWNET, }, + /* So, the mount namespace flag is called CLONE_NEWNS for historical + * reasons. Let's expose it here under a more explanatory name: "mnt". + * This is in-line with how the kernel exposes namespaces in /proc/$PID/ns. */ + [NAMESPACE_MOUNT] = { "mnt", "ns/mnt", CLONE_NEWNS, }, + [NAMESPACE_PID] = { "pid", "ns/pid", CLONE_NEWPID, }, + [NAMESPACE_USER] = { "user", "ns/user", CLONE_NEWUSER, }, + [NAMESPACE_UTS] = { "uts", "ns/uts", CLONE_NEWUTS, }, + [NAMESPACE_TIME] = { "time", "ns/time", CLONE_NEWTIME, }, + { /* Allow callers to iterate over the array without using _NAMESPACE_TYPE_MAX. */ }, +}; + +#define pid_namespace_path(pid, type) procfs_file_alloca(pid, namespace_info[type].proc_path) + +int namespace_open(pid_t pid, int *pidns_fd, int *mntns_fd, int *netns_fd, int *userns_fd, int *root_fd) { + _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, netnsfd = -1, usernsfd = -1; + int rfd = -1; + + assert(pid >= 0); + + if (mntns_fd) { + const char *mntns; + + mntns = pid_namespace_path(pid, NAMESPACE_MOUNT); + mntnsfd = open(mntns, O_RDONLY|O_NOCTTY|O_CLOEXEC); + if (mntnsfd < 0) + return -errno; + } + + if (pidns_fd) { + const char *pidns; + + pidns = pid_namespace_path(pid, NAMESPACE_PID); + pidnsfd = open(pidns, O_RDONLY|O_NOCTTY|O_CLOEXEC); + if (pidnsfd < 0) + return -errno; + } + + if (netns_fd) { + const char *netns; + + netns = pid_namespace_path(pid, NAMESPACE_NET); + netnsfd = open(netns, O_RDONLY|O_NOCTTY|O_CLOEXEC); + if (netnsfd < 0) + return -errno; + } + + if (userns_fd) { + const char *userns; + + userns = pid_namespace_path(pid, NAMESPACE_USER); + usernsfd = open(userns, O_RDONLY|O_NOCTTY|O_CLOEXEC); + if (usernsfd < 0 && errno != ENOENT) + return -errno; + } + + if (root_fd) { + const char *root; + + root = procfs_file_alloca(pid, "root"); + rfd = open(root, O_RDONLY|O_NOCTTY|O_CLOEXEC|O_DIRECTORY); + if (rfd < 0) + return -errno; + } + + if (pidns_fd) + *pidns_fd = TAKE_FD(pidnsfd); + + if (mntns_fd) + *mntns_fd = TAKE_FD(mntnsfd); + + if (netns_fd) + *netns_fd = TAKE_FD(netnsfd); + + if (userns_fd) + *userns_fd = TAKE_FD(usernsfd); + + if (root_fd) + *root_fd = TAKE_FD(rfd); + + return 0; +} + +int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int userns_fd, int root_fd) { + int r; + + if (userns_fd >= 0) { + /* Can't setns to your own userns, since then you could escalate from non-root to root in + * your own namespace, so check if namespaces are equal before attempting to enter. */ + + r = files_same(FORMAT_PROC_FD_PATH(userns_fd), "/proc/self/ns/user", 0); + if (r < 0) + return r; + if (r) + userns_fd = -1; + } + + if (pidns_fd >= 0) + if (setns(pidns_fd, CLONE_NEWPID) < 0) + return -errno; + + if (mntns_fd >= 0) + if (setns(mntns_fd, CLONE_NEWNS) < 0) + return -errno; + + if (netns_fd >= 0) + if (setns(netns_fd, CLONE_NEWNET) < 0) + return -errno; + + if (userns_fd >= 0) + if (setns(userns_fd, CLONE_NEWUSER) < 0) + return -errno; + + if (root_fd >= 0) { + if (fchdir(root_fd) < 0) + return -errno; + + if (chroot(".") < 0) + return -errno; + } + + return reset_uid_gid(); +} + +int fd_is_ns(int fd, unsigned long nsflag) { + struct statfs s; + int r; + + /* Checks whether the specified file descriptor refers to a namespace created by specifying nsflag in clone(). + * On old kernels there's no nice way to detect that, hence on those we'll return a recognizable error (EUCLEAN), + * so that callers can handle this somewhat nicely. + * + * This function returns > 0 if the fd definitely refers to a network namespace, 0 if it definitely does not + * refer to a network namespace, -EUCLEAN if we can't determine, and other negative error codes on error. */ + + if (fstatfs(fd, &s) < 0) + return -errno; + + if (!is_fs_type(&s, NSFS_MAGIC)) { + /* On really old kernels, there was no "nsfs", and network namespace sockets belonged to procfs + * instead. Handle that in a somewhat smart way. */ + + if (is_fs_type(&s, PROC_SUPER_MAGIC)) { + struct statfs t; + + /* OK, so it is procfs. Let's see if our own network namespace is procfs, too. If so, then the + * passed fd might refer to a network namespace, but we can't know for sure. In that case, + * return a recognizable error. */ + + if (statfs("/proc/self/ns/net", &t) < 0) + return -errno; + + if (s.f_type == t.f_type) + return -EUCLEAN; /* It's possible, we simply don't know */ + } + + return 0; /* No! */ + } + + r = ioctl(fd, NS_GET_NSTYPE); + if (r < 0) { + if (errno == ENOTTY) /* Old kernels didn't know this ioctl, let's also return a recognizable error in that case */ + return -EUCLEAN; + + return -errno; + } + + return (unsigned long) r == nsflag; +} + +int detach_mount_namespace(void) { + + /* Detaches the mount namespace, disabling propagation from our namespace to the host */ + + if (unshare(CLONE_NEWNS) < 0) + return -errno; + + return RET_NERRNO(mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL)); +} + +int userns_acquire(const char *uid_map, const char *gid_map) { + char path[STRLEN("/proc//uid_map") + DECIMAL_STR_MAX(pid_t) + 1]; + _cleanup_(sigkill_waitp) pid_t pid = 0; + _cleanup_close_ int userns_fd = -1; + int r; + + assert(uid_map); + assert(gid_map); + + /* Forks off a process in a new userns, configures the specified uidmap/gidmap, acquires an fd to it, + * and then kills the process again. This way we have a userns fd that is not bound to any + * process. We can use that for file system mounts and similar. */ + + r = safe_fork("(sd-mkuserns)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG|FORK_NEW_USERNS, &pid); + if (r < 0) + return r; + if (r == 0) + /* Child. We do nothing here, just freeze until somebody kills us. */ + freeze(); + + xsprintf(path, "/proc/" PID_FMT "/uid_map", pid); + r = write_string_file(path, uid_map, WRITE_STRING_FILE_DISABLE_BUFFER); + if (r < 0) + return log_error_errno(r, "Failed to write UID map: %m"); + + xsprintf(path, "/proc/" PID_FMT "/gid_map", pid); + r = write_string_file(path, gid_map, WRITE_STRING_FILE_DISABLE_BUFFER); + if (r < 0) + return log_error_errno(r, "Failed to write GID map: %m"); + + r = namespace_open(pid, NULL, NULL, NULL, &userns_fd, NULL); + if (r < 0) + return log_error_errno(r, "Failed to open userns fd: %m"); + + return TAKE_FD(userns_fd); + +} + +int in_same_namespace(pid_t pid1, pid_t pid2, NamespaceType type) { + const char *ns_path; + struct stat ns_st1, ns_st2; + + if (pid1 == 0) + pid1 = getpid_cached(); + + if (pid2 == 0) + pid2 = getpid_cached(); + + if (pid1 == pid2) + return 1; + + ns_path = pid_namespace_path(pid1, type); + if (stat(ns_path, &ns_st1) < 0) + return -errno; + + ns_path = pid_namespace_path(pid2, type); + if (stat(ns_path, &ns_st2) < 0) + return -errno; + + return stat_inode_same(&ns_st1, &ns_st2); +} |