20321298054

Committed 17 Dec 2025 11:19PM UTC coverage: 72.709% (-0.03%) from 72.736%

Build # 20321298054

Build Type

push

github

Committed by

YHNdnzj

Commit Message

core: set Result=start-limit-hit when a unit is rate limited

There is currently no way to figure out a rate limit was hit on a unit,
as the last result is stripped in order to keep reporting the first
result, which is useful in case of a watchdog failure, which is the
reason why it was changed as such.

But rate limiting is also an important information to provide to
users, so allow the Result property to reflect it when it
happens.

Run Details

6 of 7 new or added lines in 7 files covered. (85.71%)

1358 existing lines in 49 files now uncovered.

309654 of 425883 relevant lines covered (72.71%)

1138050.05 hits per line

Source File
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79.75

/src/basic/namespace-util.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>
#include <linux/magic.h>
#include <linux/nsfs.h>
#include <sched.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <unistd.h>

#include "dlfcn-util.h"
#include "errno-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "log.h"
#include "mountpoint-util.h"
#include "namespace-util.h"
#include "parse-util.h"
#include "pidfd-util.h"
#include "pidref.h"
#include "process-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "uid-range.h"
#include "user-util.h"

const struct namespace_info namespace_info[_NAMESPACE_TYPE_MAX + 1] = {
        [NAMESPACE_CGROUP] =  { "cgroup", "ns/cgroup", CLONE_NEWCGROUP, PIDFD_GET_CGROUP_NAMESPACE, PROC_CGROUP_INIT_INO },
        [NAMESPACE_IPC]    =  { "ipc",    "ns/ipc",    CLONE_NEWIPC,    PIDFD_GET_IPC_NAMESPACE,    PROC_IPC_INIT_INO    },
        [NAMESPACE_NET]    =  { "net",    "ns/net",    CLONE_NEWNET,    PIDFD_GET_NET_NAMESPACE,    0                    },
        /* 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,     PIDFD_GET_MNT_NAMESPACE,    0                    },
        [NAMESPACE_PID]    =  { "pid",    "ns/pid",    CLONE_NEWPID,    PIDFD_GET_PID_NAMESPACE,    PROC_PID_INIT_INO    },
        [NAMESPACE_USER]   =  { "user",   "ns/user",   CLONE_NEWUSER,   PIDFD_GET_USER_NAMESPACE,   PROC_USER_INIT_INO   },
        [NAMESPACE_UTS]    =  { "uts",    "ns/uts",    CLONE_NEWUTS,    PIDFD_GET_UTS_NAMESPACE,    PROC_UTS_INIT_INO    },
        [NAMESPACE_TIME]   =  { "time",   "ns/time",   CLONE_NEWTIME,   PIDFD_GET_TIME_NAMESPACE,   PROC_TIME_INIT_INO   },
        {}, /* 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)

NamespaceType clone_flag_to_namespace_type(unsigned long clone_flag) {
        for (NamespaceType t = 0; t < _NAMESPACE_TYPE_MAX; t++)
                if (((namespace_info[t].clone_flag ^ clone_flag) & (CLONE_NEWCGROUP|CLONE_NEWIPC|CLONE_NEWNET|CLONE_NEWNS|CLONE_NEWPID|CLONE_NEWUSER|CLONE_NEWUTS|CLONE_NEWTIME)) == 0)
                        return t;

        return _NAMESPACE_TYPE_INVALID;
}

bool namespace_type_supported(NamespaceType type) {
        assert(type >= 0 && type < _NAMESPACE_TYPE_MAX);

        const char *p = pid_namespace_path(0, type);
        return access(p, F_OK) >= 0;
}

static int pidref_namespace_open_by_type_internal(const PidRef *pidref, NamespaceType type, bool *need_verify) {
        int r;

        assert(pidref_is_set(pidref));
        assert(type >= 0 && type < _NAMESPACE_TYPE_MAX);

        if (pidref_is_remote(pidref))
                return -EREMOTE;

        if (pidref->fd >= 0) {
                r = pidfd_get_namespace(pidref->fd, namespace_info[type].pidfd_get_ns_ioctl_cmd);
                if (!ERRNO_IS_NEG_NOT_SUPPORTED(r))
                        return r;
        }

        if (need_verify) /* The caller shall call pidref_verify() later */
                *need_verify = true;

        _cleanup_close_ int nsfd = -EBADF;
        const char *p;

        p = pid_namespace_path(pidref->pid, type);
        nsfd = RET_NERRNO(open(p, O_RDONLY|O_NOCTTY|O_CLOEXEC));
        if (nsfd == -ENOENT) {
                r = proc_mounted();
                if (r == 0)
                        return -ENOSYS;  /* /proc/ is not available or not set up properly, we're most likely
                                            in some chroot environment. */
                if (r > 0)
                        return -ENOPKG;  /* If /proc/ is definitely around then this means the namespace type is not supported */

                /* can't determine? then propagate original error */
        }
        if (nsfd < 0)
                return nsfd;

        if (!need_verify) { /* Otherwise we verify on our own */
                r = pidref_verify(pidref);
                if (r < 0)
                        return r;
        }

        return TAKE_FD(nsfd);
}

int pidref_namespace_open_by_type(const PidRef *pidref, NamespaceType type) {
        return pidref_namespace_open_by_type_internal(pidref, type, NULL);
}

int namespace_open_by_type(NamespaceType type) {
        _cleanup_(pidref_done) PidRef self = PIDREF_NULL;
        int r;

        assert(type >= 0 && type < _NAMESPACE_TYPE_MAX);

        r = pidref_set_self(&self);
        if (r < 0)
                return r;

        return pidref_namespace_open_by_type(&self, type);
}

int pidref_namespace_open(
                const PidRef *pidref,
                int *ret_pidns_fd,
                int *ret_mntns_fd,
                int *ret_netns_fd,
                int *ret_userns_fd,
                int *ret_root_fd) {

        _cleanup_close_ int pidns_fd = -EBADF, mntns_fd = -EBADF, netns_fd = -EBADF,
                userns_fd = -EBADF, root_fd = -EBADF;
        bool need_verify = false;
        int r;

        assert(pidref_is_set(pidref));

        if (pidref_is_remote(pidref))
                return -EREMOTE;

        if (ret_pidns_fd) {
                pidns_fd = pidref_namespace_open_by_type_internal(pidref, NAMESPACE_PID, &need_verify);
                if (pidns_fd < 0)
                        return pidns_fd;
        }

        if (ret_mntns_fd) {
                mntns_fd = pidref_namespace_open_by_type_internal(pidref, NAMESPACE_MOUNT, &need_verify);
                if (mntns_fd < 0)
                        return mntns_fd;
        }

        if (ret_netns_fd) {
                netns_fd = pidref_namespace_open_by_type_internal(pidref, NAMESPACE_NET, &need_verify);
                if (netns_fd < 0)
                        return netns_fd;
        }

        if (ret_userns_fd) {
                userns_fd = pidref_namespace_open_by_type_internal(pidref, NAMESPACE_USER, &need_verify);
                if (userns_fd < 0 && userns_fd != -ENOPKG)
                        return userns_fd;
        }

        if (ret_root_fd) {
                const char *root;

                root = procfs_file_alloca(pidref->pid, "root");
                root_fd = RET_NERRNO(open(root, O_CLOEXEC|O_DIRECTORY));
                if (root_fd == -ENOENT && proc_mounted() == 0)
                        return -ENOSYS;
                if (root_fd < 0)
                        return root_fd;

                need_verify = true;
        }

        if (need_verify) {
                r = pidref_verify(pidref);
                if (r < 0)
                        return r;
        }

        if (ret_pidns_fd)
                *ret_pidns_fd = TAKE_FD(pidns_fd);

        if (ret_mntns_fd)
                *ret_mntns_fd = TAKE_FD(mntns_fd);

        if (ret_netns_fd)
                *ret_netns_fd = TAKE_FD(netns_fd);

        if (ret_userns_fd)
                *ret_userns_fd = TAKE_FD(userns_fd);

        if (ret_root_fd)
                *ret_root_fd = TAKE_FD(root_fd);

        return 0;
}

int namespace_open(
                pid_t pid,
                int *ret_pidns_fd,
                int *ret_mntns_fd,
                int *ret_netns_fd,
                int *ret_userns_fd,
                int *ret_root_fd) {

        _cleanup_(pidref_done) PidRef pidref = PIDREF_NULL;
        int r;

        r = pidref_set_pid(&pidref, pid);
        if (r < 0)
                return r;

        return pidref_namespace_open(&pidref, ret_pidns_fd, ret_mntns_fd, ret_netns_fd, ret_userns_fd, ret_root_fd);
}

int namespace_enter(int pidns_fd, int mntns_fd, int netns_fd, int userns_fd, int root_fd) {
        int r;

        /* Block dlopen() now, to avoid us inadvertently loading shared library from another namespace */
        block_dlopen();

        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 = is_our_namespace(userns_fd, NAMESPACE_USER);
                if (r < 0)
                        return r;
                if (r > 0)
                        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;
        }

        if (userns_fd >= 0)
                return reset_uid_gid();

        return 0;
}

int fd_is_namespace(int fd, NamespaceType type) {
        int r;

        /* Checks whether the specified file descriptor refers to a namespace (of type if type != _NAMESPACE_INVALID). */

        assert(fd >= 0);
        assert(type < _NAMESPACE_TYPE_MAX);

        r = fd_is_fs_type(fd, NSFS_MAGIC);
        if (r <= 0)
                return r;

        if (type < 0)
                return true;

        int clone_flag = ioctl(fd, NS_GET_NSTYPE);
        if (clone_flag < 0)
                return -errno;

        NamespaceType found_type = clone_flag_to_namespace_type(clone_flag);
        if (found_type < 0)
                return -EBADF; /* Uh? Unknown namespace type? */

        return found_type == type;
}

int is_our_namespace(int fd, NamespaceType type) {
        int r;

        assert(fd >= 0);
        assert(type < _NAMESPACE_TYPE_MAX);

        r = fd_is_namespace(fd, type);
        if (r < 0)
                return r;
        if (r == 0) /* Not a namespace or not of the right type? */
                return -EUCLEAN;

        _cleanup_close_ int our_ns = namespace_open_by_type(type);
        if (our_ns < 0)
                return our_ns;

        return fd_inode_same(fd, our_ns);
}

int namespace_is_init(NamespaceType type) {
        int r;

        assert(type >= 0);
        assert(type < _NAMESPACE_TYPE_MAX);

        if (namespace_info[type].root_inode == 0)
                return -EBADR; /* Cannot answer this question */

        const char *p = pid_namespace_path(0, type);

        struct stat st;
        r = RET_NERRNO(stat(p, &st));
        if (r == -ENOENT) {
                /* If the /proc/ns/<type> API is not around in /proc/ then ns is off in the kernel and we are in the init ns */
                r = proc_mounted();
                if (r < 0)
                        return -ENOENT; /* If we can't determine if /proc/ is mounted propagate original error */

                return r ? true : -ENOSYS;
        }
        if (r < 0)
                return r;

        return st.st_ino == namespace_info[type].root_inode;
}

int pidref_in_same_namespace(PidRef *pid1, PidRef *pid2, NamespaceType type) {
        _cleanup_close_ int ns1 = -EBADF, ns2 = -EBADF;

        /* Accepts NULL to indicate our own process */

        assert(!pid1 || pidref_is_set(pid1));
        assert(!pid2 || pidref_is_set(pid2));
        assert(type >= 0 && type < _NAMESPACE_TYPE_MAX);

        if (pidref_equal(pid1, pid2))
                return true;

        if (!pid1)
                ns1 = namespace_open_by_type(type);
        else
                ns1 = pidref_namespace_open_by_type(pid1, type);
        if (ns1 < 0)
                return ns1;

        if (!pid2)
                ns2 = namespace_open_by_type(type);
        else
                ns2 = pidref_namespace_open_by_type(pid2, type);
        if (ns2 < 0)
                return ns2;

        return fd_inode_same(ns1, ns2);
}

int in_same_namespace(pid_t pid1, pid_t pid2, NamespaceType type) {
        assert(pid1 >= 0);
        assert(pid2 >= 0);
        return pidref_in_same_namespace(pid1 == 0 ? NULL : &PIDREF_MAKE_FROM_PID(pid1),
                                        pid2 == 0 ? NULL : &PIDREF_MAKE_FROM_PID(pid2),
                                        type);
}

int namespace_get_leader(PidRef *pidref, NamespaceType type, PidRef *ret) {
        int r;

        /* Note: we don't bother with pidref_is_set()/pidref_is_remote() here, as the first call we do,
         * pidref_get_ppid_as_pidref() calls those anyway */

        assert(type >= 0 && type < _NAMESPACE_TYPE_MAX);
        assert(ret);

        _cleanup_(pidref_done) PidRef current = PIDREF_NULL;
        PidRef *c = pidref;

        for (;;) {
                _cleanup_(pidref_done) PidRef parent = PIDREF_NULL;

                r = pidref_get_ppid_as_pidref(c, &parent);
                if (r < 0)
                        return r;

                r = pidref_in_same_namespace(c, &parent, type);
                if (r < 0)
                        return r;
                if (r == 0) {
                        /* If the parent and the child are not in the same namespace, then the child is
                         * the leader we are looking for. */

                        if (pidref_is_set(&current))
                                *ret = TAKE_PIDREF(current);
                        else {
                                r = pidref_copy(c, ret);
                                if (r < 0)
                                        return r;
                        }

                        return 0;
                }

                pidref_done(&current);
                current = TAKE_PIDREF(parent);
                c = &current;
        }
}

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 detach_mount_namespace_harder(uid_t target_uid, gid_t target_gid) {
        uid_t from_uid;
        gid_t from_gid;
        int r;

        /* Tried detach_mount_namespace() first. If that doesn't work due to permissions, opens up an
         * unprivileged user namespace with a mapping of the originating UID/GID to the specified target
         * UID/GID. Then, tries detach_mount_namespace() again.
         *
         * Or in other words: tries much harder to get a mount namespace, making use of unprivileged user
         * namespaces if need be.
         *
         * Note that after this function completed:
         *
         *    → if we had privs, afterwards uids/gids on files and processes are as before
         *
         *    → if we had no privs, our own id and all our files will show up owned by target_uid/target_gid,
         *    and everything else owned by nobody.
         *
         * Yes, that's quite a difference. */

        if (!uid_is_valid(target_uid))
                return -EINVAL;
        if (!gid_is_valid(target_gid))
                return -EINVAL;

        r = detach_mount_namespace();
        if (r != -EPERM)
                return r;

        from_uid = getuid();
        from_gid = getgid();

        if (unshare(CLONE_NEWUSER) < 0)
                return log_debug_errno(errno, "Failed to acquire user namespace: %m");

        r = write_string_filef("/proc/self/uid_map", 0,
                               UID_FMT " " UID_FMT " 1\n", target_uid, from_uid);
        if (r < 0)
                return log_debug_errno(r, "Failed to write uid map: %m");

        r = write_string_file("/proc/self/setgroups", "deny", 0);
        if (r < 0)
                return log_debug_errno(r, "Failed to write setgroups file: %m");

        r = write_string_filef("/proc/self/gid_map", 0,
                               GID_FMT " " GID_FMT " 1\n", target_gid, from_gid);
        if (r < 0)
                return log_debug_errno(r, "Failed to write gid map: %m");

        return detach_mount_namespace();
}

int detach_mount_namespace_userns(int userns_fd) {
        int r;

        assert(userns_fd >= 0);

        if (setns(userns_fd, CLONE_NEWUSER) < 0)
                return log_debug_errno(errno, "Failed to join user namespace: %m");

        r = reset_uid_gid();
        if (r < 0)
                return log_debug_errno(r, "Failed to become root in user namespace: %m");

        return detach_mount_namespace();
}

int parse_userns_uid_range(const char *s, uid_t *ret_uid_shift, uid_t *ret_uid_range) {
        _cleanup_free_ char *buffer = NULL;
        const char *range, *shift;
        int r;
        uid_t uid_shift, uid_range = 65536;

        assert(s);

        range = strchr(s, ':');
        if (range) {
                buffer = strndup(s, range - s);
                if (!buffer)
                        return log_oom();
                shift = buffer;

                range++;
                r = safe_atou32(range, &uid_range);
                if (r < 0)
                        return log_error_errno(r, "Failed to parse UID range \"%s\": %m", range);
        } else
                shift = s;

        r = parse_uid(shift, &uid_shift);
        if (r < 0)
                return log_error_errno(r, "Failed to parse UID \"%s\": %m", s);

        if (!userns_shift_range_valid(uid_shift, uid_range))
                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "UID range cannot be empty or go beyond " UID_FMT ".", UID_INVALID);

        if (ret_uid_shift)
                *ret_uid_shift = uid_shift;

        if (ret_uid_range)
                *ret_uid_range = uid_range;

        return 0;
}

int userns_acquire_empty(void) {
        _cleanup_(pidref_done_sigkill_wait) PidRef pid = PIDREF_NULL;
        int r;

        r = pidref_safe_fork("(sd-mkuserns)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL|FORK_NEW_USERNS|FORK_FREEZE, &pid);
        if (r < 0)
                return r;
        assert(r > 0);

        return pidref_namespace_open_by_type(&pid, NAMESPACE_USER);
}

int userns_acquire(const char *uid_map, const char *gid_map, bool setgroups_deny) {
        char path[STRLEN("/proc//setgroups") + DECIMAL_STR_MAX(pid_t) + 1];
        _cleanup_(pidref_done_sigkill_wait) PidRef pid = PIDREF_NULL;
        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 = pidref_safe_fork("(sd-mkuserns)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL|FORK_NEW_USERNS|FORK_FREEZE, &pid);
        if (r < 0)
                return r;
        assert(r > 0);

        xsprintf(path, "/proc/" PID_FMT "/uid_map", pid.pid);
        r = write_string_file(path, uid_map, WRITE_STRING_FILE_DISABLE_BUFFER);
        if (r < 0)
                return log_debug_errno(r, "Failed to write UID map: %m");

        if (setgroups_deny) {
                xsprintf(path, "/proc/" PID_FMT "/setgroups", pid.pid);
                r = write_string_file(path, "deny", WRITE_STRING_FILE_DISABLE_BUFFER);
                if (r < 0)
                        return log_debug_errno(r, "Failed to write setgroups file: %m");
        }

        xsprintf(path, "/proc/" PID_FMT "/gid_map", pid.pid);
        r = write_string_file(path, gid_map, WRITE_STRING_FILE_DISABLE_BUFFER);
        if (r < 0)
                return log_debug_errno(r, "Failed to write GID map: %m");

        return pidref_namespace_open_by_type(&pid, NAMESPACE_USER);
}

int userns_acquire_self_root(void) {

        /* Returns a user namespace with only our own uid/gid mapped to root, and everything else unmapped.
         *
         * Note: this can be acquired unprivileged! */

        _cleanup_free_ char *uid_map = NULL, *gid_map = NULL;
        if (asprintf(&uid_map, "0 " UID_FMT " 1", getuid()) < 0)
                return -ENOMEM;
        if (asprintf(&gid_map, "0 " GID_FMT " 1", getgid()) < 0)
                return -ENOMEM;

        return userns_acquire(uid_map, gid_map, /* setgroups_deny= */ true);
}

int userns_enter_and_pin(int userns_fd, pid_t *ret_pid) {
        _cleanup_close_pair_ int pfd[2] = EBADF_PAIR;
        _cleanup_(sigkill_waitp) pid_t pid = 0;
        ssize_t n;
        char x;
        int r;

        assert(userns_fd >= 0);
        assert(ret_pid);

        if (pipe2(pfd, O_CLOEXEC) < 0)
                return -errno;

        r = safe_fork_full(
                        "(sd-pinuserns)",
                        /* stdio_fds= */ NULL,
                        (int[]) { pfd[1], userns_fd }, 2,
                        FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL,
                        &pid);
        if (r < 0)
                return r;
        if (r == 0) {
                /* Child. */

                if (setns(userns_fd, CLONE_NEWUSER) < 0) {
                        log_debug_errno(errno, "Failed to join userns: %m");
                        _exit(EXIT_FAILURE);
                }

                userns_fd = safe_close(userns_fd);

                n = write(pfd[1], &(const char) { 'x' }, 1);
                if (n < 0) {
                        log_debug_errno(errno, "Failed to write to pipe: %m");
                        _exit(EXIT_FAILURE);
                }
                assert(n == 1);

                freeze();
        }

        pfd[1] = safe_close(pfd[1]);

        n = read(pfd[0], &x, 1);
        if (n < 0)
                return -errno;
        if (n == 0)
                return -EPROTO;
        assert(n == 1);
        assert(x == 'x');

        *ret_pid = TAKE_PID(pid);
        return 0;
}

bool userns_supported(void) {
        return access("/proc/self/uid_map", F_OK) >= 0;
}

int userns_get_base_uid(int userns_fd, uid_t *ret_uid, gid_t *ret_gid) {
        _cleanup_(sigkill_waitp) pid_t pid = 0;
        int r;

        assert(userns_fd >= 0);

        r = userns_enter_and_pin(userns_fd, &pid);
        if (r < 0)
                return r;

        uid_t uid;
        r = uid_map_search_root(pid, UID_RANGE_USERNS_OUTSIDE, &uid);
        if (r < 0)
                return r;

        gid_t gid;
        r = uid_map_search_root(pid, GID_RANGE_USERNS_OUTSIDE, &gid);
        if (r < 0)
                return r;

        if (!ret_gid && uid != gid)
                return -EUCLEAN;

        if (ret_uid)
                *ret_uid = uid;
        if (ret_gid)
                *ret_gid = gid;

        return 0;
}

int process_is_owned_by_uid(const PidRef *pidref, uid_t uid) {
        int r;

        /* Checks if the specified process either is owned directly by the specified user, or if it is inside
         * a user namespace owned by it. */

        assert(uid_is_valid(uid));

        uid_t process_uid;
        r = pidref_get_uid(pidref, &process_uid);
        if (r < 0)
                return r;
        if (process_uid == uid)
                return true;

        _cleanup_close_ int userns_fd = -EBADF;
        userns_fd = pidref_namespace_open_by_type(pidref, NAMESPACE_USER);
        if (userns_fd == -ENOPKG) /* If userns is not supported, then they don't matter for ownership */
                return false;
        if (userns_fd < 0)
                return userns_fd;

        for (unsigned iteration = 0;; iteration++) {
                uid_t ns_uid;

                /* This process is in our own userns? Then we are done, in our own userns only the UIDs
                 * themselves matter. */
                r = is_our_namespace(userns_fd, NAMESPACE_USER);
                if (r < 0)
                        return r;
                if (r > 0)
                        return false;

                if (ioctl(userns_fd, NS_GET_OWNER_UID, &ns_uid) < 0)
                        return -errno;
                if (ns_uid == uid)
                        return true;

                /* Paranoia check */
                if (iteration > 16)
                        return log_debug_errno(SYNTHETIC_ERRNO(ELOOP), "Giving up while tracing parents of user namespaces after %u steps.", iteration);

                /* Go up the tree */
                _cleanup_close_ int parent_fd = ioctl(userns_fd, NS_GET_USERNS);
                if (parent_fd < 0) {
                        if (errno == EPERM) /* EPERM means we left our own userns */
                                return false;

                        return -errno;
                }

                close_and_replace(userns_fd, parent_fd);
        }
}

int is_idmapping_supported(const char *path) {
        _cleanup_close_ int mount_fd = -EBADF, userns_fd = -EBADF, dir_fd = -EBADF;
        int r;

        assert(path);

        if (!mount_new_api_supported())
                return false;

        userns_fd = r = userns_acquire_self_root();
        if (ERRNO_IS_NEG_NOT_SUPPORTED(r) || ERRNO_IS_NEG_PRIVILEGE(r) || r == -EINVAL)
                return false;
        if (r == -ENOSPC) {
                log_debug_errno(r, "Failed to acquire new user namespace, user.max_user_namespaces seems to be exhausted or maybe even zero, assuming ID-mapping is not supported: %m");
                return false;
        }
        if (r < 0)
                return log_debug_errno(r, "Failed to acquire new user namespace for checking if '%s' supports ID-mapping: %m", path);

        dir_fd = r = RET_NERRNO(open(path, O_RDONLY | O_CLOEXEC | O_NOFOLLOW));
        if (ERRNO_IS_NEG_NOT_SUPPORTED(r))
                return false;
        if (r < 0)
                return log_debug_errno(r, "Failed to open '%s', cannot determine if ID-mapping is supported: %m", path);

        mount_fd = r = RET_NERRNO(open_tree(dir_fd, "", AT_EMPTY_PATH | OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC));
        if (ERRNO_IS_NEG_NOT_SUPPORTED(r) || ERRNO_IS_NEG_PRIVILEGE(r) || r == -EINVAL)
                return false;
        if (r < 0)
                return log_debug_errno(r, "Failed to open mount tree '%s', cannot determine if ID-mapping is supported: %m", path);

        r = RET_NERRNO(mount_setattr(mount_fd, "", AT_EMPTY_PATH,
                       &(struct mount_attr) {
                                .attr_set = MOUNT_ATTR_IDMAP | MOUNT_ATTR_NOSUID | MOUNT_ATTR_NOEXEC | MOUNT_ATTR_RDONLY | MOUNT_ATTR_NODEV,
                                .userns_fd = userns_fd,
                        }, sizeof(struct mount_attr)));
        if (ERRNO_IS_NEG_NOT_SUPPORTED(r) || ERRNO_IS_NEG_PRIVILEGE(r) || r == -EINVAL)
                return false;
        if (r < 0)
                return log_debug_errno(r, "Failed to set mount attribute to '%s', cannot determine if ID-mapping is supported: %m", path);

        return true;
}

int netns_acquire(void) {
        _cleanup_(pidref_done_sigkill_wait) PidRef pid = PIDREF_NULL;
        int r;

        /* Forks off a process in a new network namespace, acquires a network namespace fd, and then kills
         * the process again. This way we have a netns fd that is not bound to any process. */

        r = pidref_safe_fork("(sd-mknetns)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL|FORK_NEW_NETNS|FORK_FREEZE, &pid);
        if (r < 0)
                return log_debug_errno(r, "Failed to fork process into new netns: %m");
        assert(r > 0);

        return pidref_namespace_open_by_type(&pid, NAMESPACE_NET);
}

systemd / systemd / 20321298054

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