/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include #include #include #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 = -EBADF, mntnsfd = -EBADF, netnsfd = -EBADF, usernsfd = -EBADF; int rfd = -EBADF; 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 = inode_same_at(userns_fd, "", AT_FDCWD, "/proc/self/ns/user", AT_EMPTY_PATH); if (r < 0) return r; if (r) userns_fd = -EBADF; } 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. Sets * propagation first to MS_SLAVE for all mounts (disabling propagation), and then back to MS_SHARED * (so that we create a new peer group). */ if (unshare(CLONE_NEWNS) < 0) return log_debug_errno(errno, "Failed to acquire mount namespace: %m"); if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0) return log_debug_errno(errno, "Failed to set mount propagation to MS_SLAVE for all mounts: %m"); if (mount(NULL, "/", NULL, MS_SHARED | MS_REC, NULL) < 0) return log_debug_errno(errno, "Failed to set mount propagation back to MS_SHARED for all mounts: %m"); return 0; } 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 = -EBADF; 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_SIGKILL|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); }