Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 929 insertions, 0 deletions

diff --git a/src/libsystemd/sd-device/device-monitor.c b/src/libsystemd/sd-device/device-monitor.c
new file mode 100644
index 0000000..bb4f9bd
--- /dev/null
+++ b/src/libsystemd/sd-device/device-monitor.c
@@ -0,0 +1,929 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <linux/filter.h>
+#include <linux/netlink.h>
+#include <linux/sockios.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "sd-device.h"
+#include "sd-event.h"
+
+#include "MurmurHash2.h"
+#include "alloc-util.h"
+#include "device-filter.h"
+#include "device-monitor-private.h"
+#include "device-private.h"
+#include "device-util.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "format-util.h"
+#include "hashmap.h"
+#include "iovec-util.h"
+#include "missing_socket.h"
+#include "mountpoint-util.h"
+#include "set.h"
+#include "socket-util.h"
+#include "stat-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "uid-range.h"
+
+#define log_monitor(m, format, ...)                                     \
+        log_debug("sd-device-monitor(%s): " format, strna(m ? m->description : NULL), ##__VA_ARGS__)
+#define log_monitor_errno(m, r, format, ...)                            \
+        log_debug_errno(r, "sd-device-monitor(%s): " format, strna(m ? m->description : NULL), ##__VA_ARGS__)
+#define log_device_monitor(d, m, format, ...)                           \
+        log_device_debug(d, "sd-device-monitor(%s): " format, strna(m ? m->description : NULL), ##__VA_ARGS__)
+#define log_device_monitor_errno(d, m, r, format, ...)                  \
+        log_device_debug_errno(d, r, "sd-device-monitor(%s): " format, strna(m ? m->description : NULL), ##__VA_ARGS__)
+
+struct sd_device_monitor {
+        unsigned n_ref;
+
+        int sock;
+        union sockaddr_union snl;
+        union sockaddr_union snl_trusted_sender;
+        bool bound;
+
+        UidRange *mapped_userns_uid_range;
+
+        Hashmap *subsystem_filter;
+        Set *tag_filter;
+        Hashmap *match_sysattr_filter;
+        Hashmap *nomatch_sysattr_filter;
+        Set *match_parent_filter;
+        Set *nomatch_parent_filter;
+        bool filter_uptodate;
+
+        sd_event *event;
+        sd_event_source *event_source;
+        char *description;
+        sd_device_monitor_handler_t callback;
+        void *userdata;
+};
+
+#define UDEV_MONITOR_MAGIC                0xfeedcafe
+
+typedef struct monitor_netlink_header {
+        /* "libudev" prefix to distinguish libudev and kernel messages */
+        char prefix[8];
+        /* Magic to protect against daemon <-> Library message format mismatch
+         * Used in the kernel from socket filter rules; needs to be stored in network order */
+        unsigned magic;
+        /* Total length of header structure known to the sender */
+        unsigned header_size;
+        /* Properties string buffer */
+        unsigned properties_off;
+        unsigned properties_len;
+        /* Hashes of primary device properties strings, to let libudev subscribers
+         * use in-kernel socket filters; values need to be stored in network order */
+        unsigned filter_subsystem_hash;
+        unsigned filter_devtype_hash;
+        unsigned filter_tag_bloom_hi;
+        unsigned filter_tag_bloom_lo;
+} monitor_netlink_header;
+
+static int monitor_set_nl_address(sd_device_monitor *m) {
+        union sockaddr_union snl;
+        socklen_t addrlen;
+
+        assert(m);
+
+        /* Get the address the kernel has assigned us.
+         * It is usually, but not necessarily the pid. */
+        addrlen = sizeof(struct sockaddr_nl);
+        if (getsockname(m->sock, &snl.sa, &addrlen) < 0)
+                return -errno;
+
+        m->snl.nl.nl_pid = snl.nl.nl_pid;
+        return 0;
+}
+
+int device_monitor_allow_unicast_sender(sd_device_monitor *m, sd_device_monitor *sender) {
+        assert(m);
+        assert(sender);
+
+        m->snl_trusted_sender.nl.nl_pid = sender->snl.nl.nl_pid;
+        return 0;
+}
+
+_public_ int sd_device_monitor_set_receive_buffer_size(sd_device_monitor *m, size_t size) {
+        assert_return(m, -EINVAL);
+
+        return fd_set_rcvbuf(m->sock, size, false);
+}
+
+int device_monitor_disconnect(sd_device_monitor *m) {
+        assert(m);
+
+        m->sock = safe_close(m->sock);
+        return 0;
+}
+
+int device_monitor_get_fd(sd_device_monitor *m) {
+        assert(m);
+
+        return m->sock;
+}
+
+int device_monitor_new_full(sd_device_monitor **ret, MonitorNetlinkGroup group, int fd) {
+        _cleanup_(sd_device_monitor_unrefp) sd_device_monitor *m = NULL;
+        _cleanup_close_ int sock = -EBADF;
+        int r;
+
+        assert(group >= 0 && group < _MONITOR_NETLINK_GROUP_MAX);
+        assert_return(ret, -EINVAL);
+
+        if (group == MONITOR_GROUP_UDEV &&
+            access("/run/udev/control", F_OK) < 0 &&
+            dev_is_devtmpfs() <= 0) {
+
+                /*
+                 * We do not support subscribing to uevents if no instance of
+                 * udev is running. Uevents would otherwise broadcast the
+                 * processing data of the host into containers, which is not
+                 * desired.
+                 *
+                 * Containers will currently not get any udev uevents, until
+                 * a supporting infrastructure is available.
+                 *
+                 * We do not set a netlink multicast group here, so the socket
+                 * will not receive any messages.
+                 */
+
+                log_monitor(m, "The udev service seems not to be active, disabling the monitor.");
+                group = MONITOR_GROUP_NONE;
+        }
+
+        if (fd < 0) {
+                sock = socket(AF_NETLINK, SOCK_RAW|SOCK_CLOEXEC|SOCK_NONBLOCK, NETLINK_KOBJECT_UEVENT);
+                if (sock < 0)
+                        return log_monitor_errno(m, errno, "Failed to create socket: %m");
+        }
+
+        m = new(sd_device_monitor, 1);
+        if (!m)
+                return -ENOMEM;
+
+        *m = (sd_device_monitor) {
+                .n_ref = 1,
+                .sock = fd >= 0 ? fd : TAKE_FD(sock),
+                .bound = fd >= 0,
+                .snl.nl.nl_family = AF_NETLINK,
+                .snl.nl.nl_groups = group,
+        };
+
+        if (fd >= 0) {
+                r = monitor_set_nl_address(m);
+                if (r < 0) {
+                        log_monitor_errno(m, r, "Failed to set netlink address: %m");
+                        goto fail;
+                }
+        }
+
+        if (DEBUG_LOGGING) {
+                _cleanup_close_ int netns = -EBADF;
+
+                /* So here's the thing: only AF_NETLINK sockets from the main network namespace will get
+                 * hardware events. Let's check if ours is from there, and if not generate a debug message,
+                 * since we cannot possibly work correctly otherwise. This is just a safety check to make
+                 * things easier to debug. */
+
+                netns = ioctl(m->sock, SIOCGSKNS);
+                if (netns < 0)
+                        log_monitor_errno(m, errno, "Unable to get network namespace of udev netlink socket, unable to determine if we are in host netns, ignoring: %m");
+                else {
+                        struct stat a, b;
+
+                        if (fstat(netns, &a) < 0) {
+                                r = log_monitor_errno(m, errno, "Failed to stat netns of udev netlink socket: %m");
+                                goto fail;
+                        }
+
+                        if (stat("/proc/1/ns/net", &b) < 0) {
+                                if (ERRNO_IS_PRIVILEGE(errno))
+                                        /* If we can't access PID1's netns info due to permissions, it's fine, this is a
+                                         * safety check only after all. */
+                                        log_monitor_errno(m, errno, "No permission to stat PID1's netns, unable to determine if we are in host netns, ignoring: %m");
+                                else
+                                        log_monitor_errno(m, errno, "Failed to stat PID1's netns, ignoring: %m");
+
+                        } else if (!stat_inode_same(&a, &b))
+                                log_monitor(m, "Netlink socket we listen on is not from host netns, we won't see device events.");
+                }
+        }
+
+        /* Let's bump the receive buffer size, but only if we are not called via socket activation, as in
+         * that case the service manager sets the receive buffer size for us, and the value in the .socket
+         * unit should take full effect. */
+        if (fd < 0) {
+                r = sd_device_monitor_set_receive_buffer_size(m, 128*1024*1024);
+                if (r < 0)
+                        log_monitor_errno(m, r, "Failed to increase receive buffer size, ignoring: %m");
+        }
+
+        *ret = TAKE_PTR(m);
+        return 0;
+
+fail:
+        /* Let's unset the socket fd in the monitor object before we destroy it so that the fd passed in is
+         * not closed on failure. */
+        if (fd >= 0)
+                m->sock = -1;
+
+        return r;
+}
+
+_public_ int sd_device_monitor_new(sd_device_monitor **ret) {
+        return device_monitor_new_full(ret, MONITOR_GROUP_UDEV, -1);
+}
+
+_public_ int sd_device_monitor_stop(sd_device_monitor *m) {
+        assert_return(m, -EINVAL);
+
+        m->event_source = sd_event_source_unref(m->event_source);
+        (void) device_monitor_disconnect(m);
+
+        return 0;
+}
+
+static int device_monitor_event_handler(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
+        _cleanup_(sd_device_unrefp) sd_device *device = NULL;
+        _unused_ _cleanup_(log_context_unrefp) LogContext *c = NULL;
+        sd_device_monitor *m = ASSERT_PTR(userdata);
+
+        if (device_monitor_receive_device(m, &device) <= 0)
+                return 0;
+
+        if (log_context_enabled())
+                c = log_context_new_strv_consume(device_make_log_fields(device));
+
+        if (m->callback)
+                return m->callback(m, device, m->userdata);
+
+        return 0;
+}
+
+_public_ int sd_device_monitor_start(sd_device_monitor *m, sd_device_monitor_handler_t callback, void *userdata) {
+        int r;
+
+        assert_return(m, -EINVAL);
+
+        if (!m->event) {
+                r = sd_device_monitor_attach_event(m, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        r = device_monitor_enable_receiving(m);
+        if (r < 0)
+                return r;
+
+        m->callback = callback;
+        m->userdata = userdata;
+
+        r = sd_event_add_io(m->event, &m->event_source, m->sock, EPOLLIN, device_monitor_event_handler, m);
+        if (r < 0)
+                return r;
+
+        (void) sd_event_source_set_description(m->event_source, m->description ?: "sd-device-monitor");
+
+        return 0;
+}
+
+_public_ int sd_device_monitor_detach_event(sd_device_monitor *m) {
+        assert_return(m, -EINVAL);
+
+        (void) sd_device_monitor_stop(m);
+        m->event = sd_event_unref(m->event);
+
+        return 0;
+}
+
+_public_ int sd_device_monitor_attach_event(sd_device_monitor *m, sd_event *event) {
+        int r;
+
+        assert_return(m, -EINVAL);
+        assert_return(!m->event, -EBUSY);
+
+        if (event)
+                m->event = sd_event_ref(event);
+        else {
+                r = sd_event_default(&m->event);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+_public_ sd_event *sd_device_monitor_get_event(sd_device_monitor *m) {
+        assert_return(m, NULL);
+
+        return m->event;
+}
+
+_public_ sd_event_source *sd_device_monitor_get_event_source(sd_device_monitor *m) {
+        assert_return(m, NULL);
+
+        return m->event_source;
+}
+
+_public_ int sd_device_monitor_set_description(sd_device_monitor *m, const char *description) {
+        int r;
+
+        assert_return(m, -EINVAL);
+
+        r = free_and_strdup(&m->description, description);
+        if (r <= 0)
+                return r;
+
+        if (m->event_source)
+                (void) sd_event_source_set_description(m->event_source, description);
+
+        return r;
+}
+
+_public_ int sd_device_monitor_get_description(sd_device_monitor *m, const char **ret) {
+        assert_return(m, -EINVAL);
+        assert_return(ret, -EINVAL);
+
+        *ret = m->description;
+        return 0;
+}
+
+int device_monitor_enable_receiving(sd_device_monitor *m) {
+        int r;
+
+        assert(m);
+
+        r = sd_device_monitor_filter_update(m);
+        if (r < 0)
+                return log_monitor_errno(m, r, "Failed to update filter: %m");
+
+        if (!m->bound) {
+                /* enable receiving of sender credentials */
+                r = setsockopt_int(m->sock, SOL_SOCKET, SO_PASSCRED, true);
+                if (r < 0)
+                        return log_monitor_errno(m, r, "Failed to set socket option SO_PASSCRED: %m");
+
+                if (bind(m->sock, &m->snl.sa, sizeof(struct sockaddr_nl)) < 0)
+                        return log_monitor_errno(m, errno, "Failed to bind monitoring socket: %m");
+
+                m->bound = true;
+
+                r = monitor_set_nl_address(m);
+                if (r < 0)
+                        return log_monitor_errno(m, r, "Failed to set address: %m");
+        }
+
+        return 0;
+}
+
+static sd_device_monitor *device_monitor_free(sd_device_monitor *m) {
+        assert(m);
+
+        (void) sd_device_monitor_detach_event(m);
+
+        uid_range_free(m->mapped_userns_uid_range);
+        free(m->description);
+        hashmap_free(m->subsystem_filter);
+        set_free(m->tag_filter);
+        hashmap_free(m->match_sysattr_filter);
+        hashmap_free(m->nomatch_sysattr_filter);
+        set_free(m->match_parent_filter);
+        set_free(m->nomatch_parent_filter);
+
+        return mfree(m);
+}
+
+DEFINE_PUBLIC_TRIVIAL_REF_UNREF_FUNC(sd_device_monitor, sd_device_monitor, device_monitor_free);
+
+static int check_subsystem_filter(sd_device_monitor *m, sd_device *device) {
+        const char *s, *subsystem, *d, *devtype = NULL;
+        int r;
+
+        assert(m);
+        assert(device);
+
+        if (hashmap_isempty(m->subsystem_filter))
+                return true;
+
+        r = sd_device_get_subsystem(device, &subsystem);
+        if (r < 0)
+                return r;
+
+        r = sd_device_get_devtype(device, &devtype);
+        if (r < 0 && r != -ENOENT)
+                return r;
+
+        HASHMAP_FOREACH_KEY(d, s, m->subsystem_filter) {
+                if (!streq(s, subsystem))
+                        continue;
+
+                if (!d || streq_ptr(d, devtype))
+                        return true;
+        }
+
+        return false;
+}
+
+static bool check_tag_filter(sd_device_monitor *m, sd_device *device) {
+        const char *tag;
+
+        assert(m);
+        assert(device);
+
+        if (set_isempty(m->tag_filter))
+                return true;
+
+        SET_FOREACH(tag, m->tag_filter)
+                if (sd_device_has_tag(device, tag) > 0)
+                        return true;
+
+        return false;
+}
+
+static int passes_filter(sd_device_monitor *m, sd_device *device) {
+        int r;
+
+        assert(m);
+        assert(device);
+
+        r = check_subsystem_filter(m, device);
+        if (r <= 0)
+                return r;
+
+        if (!check_tag_filter(m, device))
+                return false;
+
+        if (!device_match_sysattr(device, m->match_sysattr_filter, m->nomatch_sysattr_filter))
+                return false;
+
+        return device_match_parent(device, m->match_parent_filter, m->nomatch_parent_filter);
+}
+
+static bool check_sender_uid(sd_device_monitor *m, uid_t uid) {
+        int r;
+
+        assert(m);
+
+        /* Always trust messages from uid 0. */
+        if (uid == 0)
+                return true;
+
+        /* Trust messages sent by the same UID we are running. Currently, such situation happens only for
+         * unicast messages. */
+        if (uid == getuid() || uid == geteuid())
+                return true;
+
+        if (!m->mapped_userns_uid_range) {
+                r = uid_range_load_userns(&m->mapped_userns_uid_range, NULL);
+                if (r < 0)
+                        log_monitor_errno(m, r, "Failed to load UID ranges mapped to the current user namespace, ignoring: %m");
+        }
+
+        /* Trust messages come from outside of the current user namespace. */
+        if (!uid_range_contains(m->mapped_userns_uid_range, uid))
+                return true;
+
+        /* Otherwise, refuse messages. */
+        return false;
+}
+
+int device_monitor_receive_device(sd_device_monitor *m, sd_device **ret) {
+        _cleanup_(sd_device_unrefp) sd_device *device = NULL;
+        _cleanup_free_ uint8_t *buf_alloc = NULL;
+        union {
+                monitor_netlink_header *nlh;
+                char *nulstr;
+                uint8_t *buf;
+        } message;
+        struct iovec iov;
+        CMSG_BUFFER_TYPE(CMSG_SPACE(sizeof(struct ucred))) control;
+        union sockaddr_union snl;
+        struct msghdr smsg = {
+                .msg_iov = &iov,
+                .msg_iovlen = 1,
+                .msg_control = &control,
+                .msg_controllen = sizeof(control),
+                .msg_name = &snl,
+                .msg_namelen = sizeof(snl),
+        };
+        struct ucred *cred;
+        size_t offset;
+        ssize_t n;
+        bool is_initialized = false;
+        int r;
+
+        assert(m);
+        assert(ret);
+
+        n = next_datagram_size_fd(m->sock);
+        if (n < 0) {
+                if (!ERRNO_IS_TRANSIENT(n))
+                        log_monitor_errno(m, n, "Failed to get the received message size: %m");
+                return n;
+        }
+
+        if ((size_t) n < ALLOCA_MAX / sizeof(uint8_t) / 2)
+                message.buf = newa(uint8_t, n);
+        else {
+                buf_alloc = new(uint8_t, n);
+                if (!buf_alloc)
+                        return log_oom_debug();
+
+                message.buf = buf_alloc;
+        }
+
+        iov = IOVEC_MAKE(message.buf, n);
+
+        n = recvmsg(m->sock, &smsg, 0);
+        if (n < 0) {
+                if (!ERRNO_IS_TRANSIENT(errno))
+                        log_monitor_errno(m, errno, "Failed to receive message: %m");
+                return -errno;
+        }
+
+        if (smsg.msg_flags & MSG_TRUNC)
+                return log_monitor_errno(m, SYNTHETIC_ERRNO(EINVAL), "Received truncated message, ignoring message.");
+
+        if (n < 32)
+                return log_monitor_errno(m, SYNTHETIC_ERRNO(EINVAL), "Invalid message length (%zi), ignoring message.", n);
+
+        if (snl.nl.nl_groups == MONITOR_GROUP_NONE) {
+                /* unicast message, check if we trust the sender */
+                if (m->snl_trusted_sender.nl.nl_pid == 0 ||
+                    snl.nl.nl_pid != m->snl_trusted_sender.nl.nl_pid)
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                                 "Unicast netlink message ignored.");
+
+        } else if (snl.nl.nl_groups == MONITOR_GROUP_KERNEL) {
+                if (snl.nl.nl_pid > 0)
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                                 "Multicast kernel netlink message from PID %"PRIu32" ignored.",
+                                                 snl.nl.nl_pid);
+        }
+
+        cred = CMSG_FIND_DATA(&smsg, SOL_SOCKET, SCM_CREDENTIALS, struct ucred);
+        if (!cred)
+                return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                         "No sender credentials received, ignoring message.");
+
+        if (!check_sender_uid(m, cred->uid))
+                return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                         "Sender uid="UID_FMT", message ignored.", cred->uid);
+
+        if (!memchr(message.buf, 0, n))
+                return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN), "Received message without NUL, ignoring message.");
+
+        if (streq(message.nulstr, "libudev")) {
+                /* udev message needs proper version magic */
+                if (message.nlh->magic != htobe32(UDEV_MONITOR_MAGIC))
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                                 "Invalid message signature (%x != %x).",
+                                                 message.nlh->magic, htobe32(UDEV_MONITOR_MAGIC));
+
+                if (message.nlh->properties_off + 32 > (size_t) n)
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN),
+                                                 "Invalid offset for properties (%u > %zi).",
+                                                 message.nlh->properties_off + 32, n);
+
+                offset = message.nlh->properties_off;
+
+                /* devices received from udev are always initialized */
+                is_initialized = true;
+
+        } else {
+                /* check kernel message header */
+                if (!strstr(message.nulstr, "@/"))
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN), "Invalid message header.");
+
+                offset = strlen(message.nulstr) + 1;
+                if (offset >= (size_t) n)
+                        return log_monitor_errno(m, SYNTHETIC_ERRNO(EAGAIN), "Invalid message length.");
+        }
+
+        r = device_new_from_nulstr(&device, message.nulstr + offset, n - offset);
+        if (r < 0)
+                return log_monitor_errno(m, r, "Failed to create device from received message: %m");
+
+        if (is_initialized)
+                device_set_is_initialized(device);
+
+        /* Skip device, if it does not pass the current filter */
+        r = passes_filter(m, device);
+        if (r < 0)
+                return log_device_monitor_errno(device, m, r, "Failed to check received device passing filter: %m");
+        if (r == 0)
+                log_device_monitor(device, m, "Received device does not pass filter, ignoring.");
+        else
+                *ret = TAKE_PTR(device);
+
+        return r;
+}
+
+static uint32_t string_hash32(const char *str) {
+        return MurmurHash2(str, strlen(str), 0);
+}
+
+/* Get a bunch of bit numbers out of the hash, and set the bits in our bit field */
+static uint64_t string_bloom64(const char *str) {
+        uint64_t bits = 0;
+        uint32_t hash = string_hash32(str);
+
+        bits |= UINT64_C(1) << (hash & 63);
+        bits |= UINT64_C(1) << ((hash >> 6) & 63);
+        bits |= UINT64_C(1) << ((hash >> 12) & 63);
+        bits |= UINT64_C(1) << ((hash >> 18) & 63);
+        return bits;
+}
+
+int device_monitor_send_device(
+                sd_device_monitor *m,
+                sd_device_monitor *destination,
+                sd_device *device) {
+
+        monitor_netlink_header nlh = {
+                .prefix = "libudev",
+                .magic = htobe32(UDEV_MONITOR_MAGIC),
+                .header_size = sizeof nlh,
+        };
+        struct iovec iov[2] = {
+                { .iov_base = &nlh, .iov_len = sizeof nlh },
+        };
+        struct msghdr smsg = {
+                .msg_iov = iov,
+                .msg_iovlen = 2,
+        };
+        /* default destination for sending */
+        union sockaddr_union default_destination = {
+                .nl.nl_family = AF_NETLINK,
+                .nl.nl_groups = MONITOR_GROUP_UDEV,
+        };
+        uint64_t tag_bloom_bits;
+        const char *buf, *val;
+        ssize_t count;
+        size_t blen;
+        int r;
+
+        assert(m);
+        assert(device);
+
+        r = device_get_properties_nulstr(device, &buf, &blen);
+        if (r < 0)
+                return log_device_monitor_errno(device, m, r, "Failed to get device properties: %m");
+        if (blen < 32)
+                return log_device_monitor_errno(device, m, SYNTHETIC_ERRNO(EINVAL),
+                                                "Length of device property nulstr is too small to contain valid device information.");
+
+        /* fill in versioned header */
+        r = sd_device_get_subsystem(device, &val);
+        if (r < 0)
+                return log_device_monitor_errno(device, m, r, "Failed to get device subsystem: %m");
+        nlh.filter_subsystem_hash = htobe32(string_hash32(val));
+
+        if (sd_device_get_devtype(device, &val) >= 0)
+                nlh.filter_devtype_hash = htobe32(string_hash32(val));
+
+        /* add tag bloom filter */
+        tag_bloom_bits = 0;
+        FOREACH_DEVICE_TAG(device, tag)
+                tag_bloom_bits |= string_bloom64(tag);
+
+        if (tag_bloom_bits > 0) {
+                nlh.filter_tag_bloom_hi = htobe32(tag_bloom_bits >> 32);
+                nlh.filter_tag_bloom_lo = htobe32(tag_bloom_bits & 0xffffffff);
+        }
+
+        /* add properties list */
+        nlh.properties_off = iov[0].iov_len;
+        nlh.properties_len = blen;
+        iov[1] = IOVEC_MAKE((char*) buf, blen);
+
+        /*
+         * Use custom address for target, or the default one.
+         *
+         * If we send to a multicast group, we will get
+         * ECONNREFUSED, which is expected.
+         */
+        smsg.msg_name = destination ? &destination->snl : &default_destination;
+        smsg.msg_namelen = sizeof(struct sockaddr_nl);
+        count = sendmsg(m->sock, &smsg, 0);
+        if (count < 0) {
+                if (!destination && errno == ECONNREFUSED) {
+                        log_device_monitor(device, m, "Passed to netlink monitor.");
+                        return 0;
+                } else
+                        return log_device_monitor_errno(device, m, errno, "Failed to send device to netlink monitor: %m");
+        }
+
+        log_device_monitor(device, m, "Passed %zi byte to netlink monitor.", count);
+        return count;
+}
+
+static void bpf_stmt(struct sock_filter *ins, unsigned *i,
+                     unsigned short code, unsigned data) {
+        ins[(*i)++] = (struct sock_filter) {
+                .code = code,
+                .k = data,
+        };
+}
+
+static void bpf_jmp(struct sock_filter *ins, unsigned *i,
+                    unsigned short code, unsigned data,
+                    unsigned short jt, unsigned short jf) {
+        ins[(*i)++] = (struct sock_filter) {
+                .code = code,
+                .jt = jt,
+                .jf = jf,
+                .k = data,
+        };
+}
+
+_public_ int sd_device_monitor_filter_update(sd_device_monitor *m) {
+        struct sock_filter ins[512] = {};
+        struct sock_fprog filter;
+        const char *subsystem, *devtype, *tag;
+        unsigned i = 0;
+
+        assert_return(m, -EINVAL);
+
+        if (m->filter_uptodate)
+                return 0;
+
+        if (m->snl.nl.nl_groups == MONITOR_GROUP_KERNEL ||
+            (hashmap_isempty(m->subsystem_filter) &&
+             set_isempty(m->tag_filter))) {
+                m->filter_uptodate = true;
+                return 0;
+        }
+
+        /* load magic in A */
+        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(monitor_netlink_header, magic));
+        /* jump if magic matches */
+        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, UDEV_MONITOR_MAGIC, 1, 0);
+        /* wrong magic, pass packet */
+        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+        if (!set_isempty(m->tag_filter)) {
+                int tag_matches = set_size(m->tag_filter);
+
+                /* add all tags matches */
+                SET_FOREACH(tag, m->tag_filter) {
+                        uint64_t tag_bloom_bits = string_bloom64(tag);
+                        uint32_t tag_bloom_hi = tag_bloom_bits >> 32;
+                        uint32_t tag_bloom_lo = tag_bloom_bits & 0xffffffff;
+
+                        /* load device bloom bits in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(monitor_netlink_header, filter_tag_bloom_hi));
+                        /* clear bits (tag bits & bloom bits) */
+                        bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_hi);
+                        /* jump to next tag if it does not match */
+                        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_hi, 0, 3);
+
+                        /* load device bloom bits in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(monitor_netlink_header, filter_tag_bloom_lo));
+                        /* clear bits (tag bits & bloom bits) */
+                        bpf_stmt(ins, &i, BPF_ALU|BPF_AND|BPF_K, tag_bloom_lo);
+                        /* jump behind end of tag match block if tag matches */
+                        tag_matches--;
+                        bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, tag_bloom_lo, 1 + (tag_matches * 6), 0);
+                }
+
+                /* nothing matched, drop packet */
+                bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
+        }
+
+        /* add all subsystem matches */
+        if (!hashmap_isempty(m->subsystem_filter)) {
+                HASHMAP_FOREACH_KEY(devtype, subsystem, m->subsystem_filter) {
+                        uint32_t hash = string_hash32(subsystem);
+
+                        /* load device subsystem value in A */
+                        bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(monitor_netlink_header, filter_subsystem_hash));
+                        if (!devtype) {
+                                /* jump if subsystem does not match */
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
+                        } else {
+                                /* jump if subsystem does not match */
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 3);
+                                /* load device devtype value in A */
+                                bpf_stmt(ins, &i, BPF_LD|BPF_W|BPF_ABS, offsetof(monitor_netlink_header, filter_devtype_hash));
+                                /* jump if value does not match */
+                                hash = string_hash32(devtype);
+                                bpf_jmp(ins, &i, BPF_JMP|BPF_JEQ|BPF_K, hash, 0, 1);
+                        }
+
+                        /* matched, pass packet */
+                        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+                        if (i+1 >= ELEMENTSOF(ins))
+                                return -E2BIG;
+                }
+
+                /* nothing matched, drop packet */
+                bpf_stmt(ins, &i, BPF_RET|BPF_K, 0);
+        }
+
+        /* matched, pass packet */
+        bpf_stmt(ins, &i, BPF_RET|BPF_K, 0xffffffff);
+
+        /* install filter */
+        filter = (struct sock_fprog) {
+                .len = i,
+                .filter = ins,
+        };
+        if (setsockopt(m->sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) < 0)
+                return -errno;
+
+        m->filter_uptodate = true;
+        return 0;
+}
+
+_public_ int sd_device_monitor_filter_add_match_subsystem_devtype(sd_device_monitor *m, const char *subsystem, const char *devtype) {
+        int r;
+
+        assert_return(m, -EINVAL);
+        assert_return(subsystem, -EINVAL);
+
+        /* Do not use string_has_ops_free_free or hashmap_put_strdup() here, as this may be called
+         * multiple times with the same subsystem but different devtypes. */
+        r = hashmap_put_strdup_full(&m->subsystem_filter, &trivial_hash_ops_free_free, subsystem, devtype);
+        if (r <= 0)
+                return r;
+
+        m->filter_uptodate = false;
+        return r;
+}
+
+_public_ int sd_device_monitor_filter_add_match_tag(sd_device_monitor *m, const char *tag) {
+        int r;
+
+        assert_return(m, -EINVAL);
+        assert_return(tag, -EINVAL);
+
+        r = set_put_strdup(&m->tag_filter, tag);
+        if (r <= 0)
+                return r;
+
+        m->filter_uptodate = false;
+        return r;
+}
+
+_public_ int sd_device_monitor_filter_add_match_sysattr(sd_device_monitor *m, const char *sysattr, const char *value, int match) {
+        Hashmap **hashmap;
+
+        assert_return(m, -EINVAL);
+        assert_return(sysattr, -EINVAL);
+
+        if (match)
+                hashmap = &m->match_sysattr_filter;
+        else
+                hashmap = &m->nomatch_sysattr_filter;
+
+        /* TODO: unset m->filter_uptodate on success when we support this filter on BPF. */
+        return update_match_strv(hashmap, sysattr, value, /* clear_on_null = */ true);
+}
+
+_public_ int sd_device_monitor_filter_add_match_parent(sd_device_monitor *m, sd_device *device, int match) {
+        const char *syspath;
+        Set **set;
+        int r;
+
+        assert_return(m, -EINVAL);
+        assert_return(device, -EINVAL);
+
+        r = sd_device_get_syspath(device, &syspath);
+        if (r < 0)
+                return r;
+
+        if (match)
+                set = &m->match_parent_filter;
+        else
+                set = &m->nomatch_parent_filter;
+
+        /* TODO: unset m->filter_uptodate on success when we support this filter on BPF. */
+        return set_put_strdup(set, syspath);
+}
+
+_public_ int sd_device_monitor_filter_remove(sd_device_monitor *m) {
+        static const struct sock_fprog filter = { 0, NULL };
+
+        assert_return(m, -EINVAL);
+
+        m->subsystem_filter = hashmap_free(m->subsystem_filter);
+        m->tag_filter = set_free(m->tag_filter);
+        m->match_sysattr_filter = hashmap_free(m->match_sysattr_filter);
+        m->nomatch_sysattr_filter = hashmap_free(m->nomatch_sysattr_filter);
+        m->match_parent_filter = set_free(m->match_parent_filter);
+        m->nomatch_parent_filter = set_free(m->nomatch_parent_filter);
+
+        if (setsockopt(m->sock, SOL_SOCKET, SO_DETACH_FILTER, &filter, sizeof(filter)) < 0)
+                return -errno;
+
+        m->filter_uptodate = true;
+        return 0;
+}