Adding upstream version 247.3.upstream/247.3upstream

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

1 files changed, 1348 insertions, 0 deletions

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
new file mode 100644
index 0000000..4881fd0
--- /dev/null
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -0,0 +1,1348 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <endian.h>
+#include <poll.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "sd-bus.h"
+#include "sd-daemon.h"
+
+#include "alloc-util.h"
+#include "bus-internal.h"
+#include "bus-message.h"
+#include "bus-socket.h"
+#include "fd-util.h"
+#include "format-util.h"
+#include "fs-util.h"
+#include "hexdecoct.h"
+#include "io-util.h"
+#include "macro.h"
+#include "memory-util.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "rlimit-util.h"
+#include "selinux-util.h"
+#include "signal-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "user-util.h"
+#include "utf8.h"
+
+#define SNDBUF_SIZE (8*1024*1024)
+
+static void iovec_advance(struct iovec iov[], unsigned *idx, size_t size) {
+
+        while (size > 0) {
+                struct iovec *i = iov + *idx;
+
+                if (i->iov_len > size) {
+                        i->iov_base = (uint8_t*) i->iov_base + size;
+                        i->iov_len -= size;
+                        return;
+                }
+
+                size -= i->iov_len;
+
+                *i = IOVEC_MAKE(NULL, 0);
+
+                (*idx)++;
+        }
+}
+
+static int append_iovec(sd_bus_message *m, const void *p, size_t sz) {
+        assert(m);
+        assert(p);
+        assert(sz > 0);
+
+        m->iovec[m->n_iovec++] = IOVEC_MAKE((void*) p, sz);
+
+        return 0;
+}
+
+static int bus_message_setup_iovec(sd_bus_message *m) {
+        struct bus_body_part *part;
+        unsigned n, i;
+        int r;
+
+        assert(m);
+        assert(m->sealed);
+
+        if (m->n_iovec > 0)
+                return 0;
+
+        assert(!m->iovec);
+
+        n = 1 + m->n_body_parts;
+        if (n < ELEMENTSOF(m->iovec_fixed))
+                m->iovec = m->iovec_fixed;
+        else {
+                m->iovec = new(struct iovec, n);
+                if (!m->iovec) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+        }
+
+        r = append_iovec(m, m->header, BUS_MESSAGE_BODY_BEGIN(m));
+        if (r < 0)
+                goto fail;
+
+        MESSAGE_FOREACH_PART(part, i, m)  {
+                r = bus_body_part_map(part);
+                if (r < 0)
+                        goto fail;
+
+                r = append_iovec(m, part->data, part->size);
+                if (r < 0)
+                        goto fail;
+        }
+
+        assert(n == m->n_iovec);
+
+        return 0;
+
+fail:
+        m->poisoned = true;
+        return r;
+}
+
+bool bus_socket_auth_needs_write(sd_bus *b) {
+
+        unsigned i;
+
+        if (b->auth_index >= ELEMENTSOF(b->auth_iovec))
+                return false;
+
+        for (i = b->auth_index; i < ELEMENTSOF(b->auth_iovec); i++) {
+                struct iovec *j = b->auth_iovec + i;
+
+                if (j->iov_len > 0)
+                        return true;
+        }
+
+        return false;
+}
+
+static int bus_socket_write_auth(sd_bus *b) {
+        ssize_t k;
+
+        assert(b);
+        assert(b->state == BUS_AUTHENTICATING);
+
+        if (!bus_socket_auth_needs_write(b))
+                return 0;
+
+        if (b->prefer_writev)
+                k = writev(b->output_fd, b->auth_iovec + b->auth_index, ELEMENTSOF(b->auth_iovec) - b->auth_index);
+        else {
+                struct msghdr mh = {
+                        .msg_iov = b->auth_iovec + b->auth_index,
+                        .msg_iovlen = ELEMENTSOF(b->auth_iovec) - b->auth_index,
+                };
+
+                k = sendmsg(b->output_fd, &mh, MSG_DONTWAIT|MSG_NOSIGNAL);
+                if (k < 0 && errno == ENOTSOCK) {
+                        b->prefer_writev = true;
+                        k = writev(b->output_fd, b->auth_iovec + b->auth_index, ELEMENTSOF(b->auth_iovec) - b->auth_index);
+                }
+        }
+
+        if (k < 0)
+                return errno == EAGAIN ? 0 : -errno;
+
+        iovec_advance(b->auth_iovec, &b->auth_index, (size_t) k);
+        return 1;
+}
+
+static int bus_socket_auth_verify_client(sd_bus *b) {
+        char *d, *e, *f, *start;
+        sd_id128_t peer;
+        int r;
+
+        assert(b);
+
+        /*
+         * We expect three response lines:
+         *   "DATA\r\n"
+         *   "OK <server-id>\r\n"
+         *   "AGREE_UNIX_FD\r\n"        (optional)
+         */
+
+        d = memmem_safe(b->rbuffer, b->rbuffer_size, "\r\n", 2);
+        if (!d)
+                return 0;
+
+        e = memmem(d + 2, b->rbuffer_size - (d - (char*) b->rbuffer) - 2, "\r\n", 2);
+        if (!e)
+                return 0;
+
+        if (b->accept_fd) {
+                f = memmem(e + 2, b->rbuffer_size - (e - (char*) b->rbuffer) - 2, "\r\n", 2);
+                if (!f)
+                        return 0;
+
+                start = f + 2;
+        } else {
+                f = NULL;
+                start = e + 2;
+        }
+
+        /* Nice! We got all the lines we need. First check the DATA line. */
+
+        if (d - (char*) b->rbuffer == 4) {
+                if (memcmp(b->rbuffer, "DATA", 4))
+                        return -EPERM;
+        } else if (d - (char*) b->rbuffer == 3 + 32) {
+                /*
+                 * Old versions of the server-side implementation of `sd-bus` replied with "OK <id>" to
+                 * "AUTH" requests from a client, even if the "AUTH" line did not contain inlined
+                 * arguments. Therefore, we also accept "OK <id>" here, even though it is technically the
+                 * wrong reply. We ignore the "<id>" parameter, though, since it has no real value.
+                 */
+                if (memcmp(b->rbuffer, "OK ", 3))
+                        return -EPERM;
+        } else
+                return -EPERM;
+
+        /* Now check the OK line. */
+
+        if (e - d != 2 + 3 + 32)
+                return -EPERM;
+
+        if (memcmp(d + 2, "OK ", 3))
+                return -EPERM;
+
+        b->auth = b->anonymous_auth ? BUS_AUTH_ANONYMOUS : BUS_AUTH_EXTERNAL;
+
+        for (unsigned i = 0; i < 32; i += 2) {
+                int x, y;
+
+                x = unhexchar(d[2 + 3 + i]);
+                y = unhexchar(d[2 + 3 + i + 1]);
+
+                if (x < 0 || y < 0)
+                        return -EINVAL;
+
+                peer.bytes[i/2] = ((uint8_t) x << 4 | (uint8_t) y);
+        }
+
+        if (!sd_id128_is_null(b->server_id) &&
+            !sd_id128_equal(b->server_id, peer))
+                return -EPERM;
+
+        b->server_id = peer;
+
+        /* And possibly check the third line, too */
+
+        if (f)
+                b->can_fds =
+                        (f - e == STRLEN("\r\nAGREE_UNIX_FD")) &&
+                        memcmp(e + 2, "AGREE_UNIX_FD",
+                               STRLEN("AGREE_UNIX_FD")) == 0;
+
+        b->rbuffer_size -= (start - (char*) b->rbuffer);
+        memmove(b->rbuffer, start, b->rbuffer_size);
+
+        r = bus_start_running(b);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static bool line_equals(const char *s, size_t m, const char *line) {
+        size_t l;
+
+        l = strlen(line);
+        if (l != m)
+                return false;
+
+        return memcmp(s, line, l) == 0;
+}
+
+static bool line_begins(const char *s, size_t m, const char *word) {
+        const char *p;
+
+        p = memory_startswith(s, m, word);
+        return p && (p == (s + m) || *p == ' ');
+}
+
+static int verify_anonymous_token(sd_bus *b, const char *p, size_t l) {
+        _cleanup_free_ char *token = NULL;
+        size_t len;
+        int r;
+
+        if (!b->anonymous_auth)
+                return 0;
+
+        if (l <= 0)
+                return 1;
+
+        assert(p[0] == ' ');
+        p++; l--;
+
+        if (l % 2 != 0)
+                return 0;
+
+        r = unhexmem(p, l, (void **) &token, &len);
+        if (r < 0)
+                return 0;
+
+        if (memchr(token, 0, len))
+                return 0;
+
+        return !!utf8_is_valid(token);
+}
+
+static int verify_external_token(sd_bus *b, const char *p, size_t l) {
+        _cleanup_free_ char *token = NULL;
+        size_t len;
+        uid_t u;
+        int r;
+
+        /* We don't do any real authentication here. Instead, we if
+         * the owner of this bus wanted authentication he should have
+         * checked SO_PEERCRED before even creating the bus object. */
+
+        if (!b->anonymous_auth && !b->ucred_valid)
+                return 0;
+
+        if (l <= 0)
+                return 1;
+
+        assert(p[0] == ' ');
+        p++; l--;
+
+        if (l % 2 != 0)
+                return 0;
+
+        r = unhexmem(p, l, (void**) &token, &len);
+        if (r < 0)
+                return 0;
+
+        if (memchr(token, 0, len))
+                return 0;
+
+        r = parse_uid(token, &u);
+        if (r < 0)
+                return 0;
+
+        /* We ignore the passed value if anonymous authentication is
+         * on anyway. */
+        if (!b->anonymous_auth && u != b->ucred.uid)
+                return 0;
+
+        return 1;
+}
+
+static int bus_socket_auth_write(sd_bus *b, const char *t) {
+        char *p;
+        size_t l;
+
+        assert(b);
+        assert(t);
+
+        /* We only make use of the first iovec */
+        assert(IN_SET(b->auth_index, 0, 1));
+
+        l = strlen(t);
+        p = malloc(b->auth_iovec[0].iov_len + l);
+        if (!p)
+                return -ENOMEM;
+
+        memcpy_safe(p, b->auth_iovec[0].iov_base, b->auth_iovec[0].iov_len);
+        memcpy(p + b->auth_iovec[0].iov_len, t, l);
+
+        b->auth_iovec[0].iov_base = p;
+        b->auth_iovec[0].iov_len += l;
+
+        free(b->auth_buffer);
+        b->auth_buffer = p;
+        b->auth_index = 0;
+        return 0;
+}
+
+static int bus_socket_auth_write_ok(sd_bus *b) {
+        char t[3 + 32 + 2 + 1];
+
+        assert(b);
+
+        xsprintf(t, "OK " SD_ID128_FORMAT_STR "\r\n", SD_ID128_FORMAT_VAL(b->server_id));
+
+        return bus_socket_auth_write(b, t);
+}
+
+static int bus_socket_auth_verify_server(sd_bus *b) {
+        char *e;
+        const char *line;
+        size_t l;
+        bool processed = false;
+        int r;
+
+        assert(b);
+
+        if (b->rbuffer_size < 1)
+                return 0;
+
+        /* First char must be a NUL byte */
+        if (*(char*) b->rbuffer != 0)
+                return -EIO;
+
+        if (b->rbuffer_size < 3)
+                return 0;
+
+        /* Begin with the first line */
+        if (b->auth_rbegin <= 0)
+                b->auth_rbegin = 1;
+
+        for (;;) {
+                /* Check if line is complete */
+                line = (char*) b->rbuffer + b->auth_rbegin;
+                e = memmem(line, b->rbuffer_size - b->auth_rbegin, "\r\n", 2);
+                if (!e)
+                        return processed;
+
+                l = e - line;
+
+                if (line_begins(line, l, "AUTH ANONYMOUS")) {
+
+                        r = verify_anonymous_token(b,
+                                                   line + strlen("AUTH ANONYMOUS"),
+                                                   l - strlen("AUTH ANONYMOUS"));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                r = bus_socket_auth_write(b, "REJECTED\r\n");
+                        else {
+                                b->auth = BUS_AUTH_ANONYMOUS;
+                                if (l <= strlen("AUTH ANONYMOUS"))
+                                        r = bus_socket_auth_write(b, "DATA\r\n");
+                                else
+                                        r = bus_socket_auth_write_ok(b);
+                        }
+
+                } else if (line_begins(line, l, "AUTH EXTERNAL")) {
+
+                        r = verify_external_token(b,
+                                                  line + strlen("AUTH EXTERNAL"),
+                                                  l - strlen("AUTH EXTERNAL"));
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                r = bus_socket_auth_write(b, "REJECTED\r\n");
+                        else {
+                                b->auth = BUS_AUTH_EXTERNAL;
+                                if (l <= strlen("AUTH EXTERNAL"))
+                                        r = bus_socket_auth_write(b, "DATA\r\n");
+                                else
+                                        r = bus_socket_auth_write_ok(b);
+                        }
+
+                } else if (line_begins(line, l, "AUTH"))
+                        r = bus_socket_auth_write(b, "REJECTED EXTERNAL ANONYMOUS\r\n");
+                else if (line_equals(line, l, "CANCEL") ||
+                         line_begins(line, l, "ERROR")) {
+
+                        b->auth = _BUS_AUTH_INVALID;
+                        r = bus_socket_auth_write(b, "REJECTED\r\n");
+
+                } else if (line_equals(line, l, "BEGIN")) {
+
+                        if (b->auth == _BUS_AUTH_INVALID)
+                                r = bus_socket_auth_write(b, "ERROR\r\n");
+                        else {
+                                /* We can't leave from the auth phase
+                                 * before we haven't written
+                                 * everything queued, so let's check
+                                 * that */
+
+                                if (bus_socket_auth_needs_write(b))
+                                        return 1;
+
+                                b->rbuffer_size -= (e + 2 - (char*) b->rbuffer);
+                                memmove(b->rbuffer, e + 2, b->rbuffer_size);
+                                return bus_start_running(b);
+                        }
+
+                } else if (line_begins(line, l, "DATA")) {
+
+                        if (b->auth == _BUS_AUTH_INVALID)
+                                r = bus_socket_auth_write(b, "ERROR\r\n");
+                        else {
+                                if (b->auth == BUS_AUTH_ANONYMOUS)
+                                        r = verify_anonymous_token(b, line + 4, l - 4);
+                                else
+                                        r = verify_external_token(b, line + 4, l - 4);
+
+                                if (r < 0)
+                                        return r;
+                                if (r == 0) {
+                                        b->auth = _BUS_AUTH_INVALID;
+                                        r = bus_socket_auth_write(b, "REJECTED\r\n");
+                                } else
+                                        r = bus_socket_auth_write_ok(b);
+                        }
+                } else if (line_equals(line, l, "NEGOTIATE_UNIX_FD")) {
+                        if (b->auth == _BUS_AUTH_INVALID || !b->accept_fd)
+                                r = bus_socket_auth_write(b, "ERROR\r\n");
+                        else {
+                                b->can_fds = true;
+                                r = bus_socket_auth_write(b, "AGREE_UNIX_FD\r\n");
+                        }
+                } else
+                        r = bus_socket_auth_write(b, "ERROR\r\n");
+
+                if (r < 0)
+                        return r;
+
+                b->auth_rbegin = e + 2 - (char*) b->rbuffer;
+
+                processed = true;
+        }
+}
+
+static int bus_socket_auth_verify(sd_bus *b) {
+        assert(b);
+
+        if (b->is_server)
+                return bus_socket_auth_verify_server(b);
+        else
+                return bus_socket_auth_verify_client(b);
+}
+
+static int bus_socket_read_auth(sd_bus *b) {
+        struct msghdr mh;
+        struct iovec iov = {};
+        size_t n;
+        ssize_t k;
+        int r;
+        void *p;
+        CMSG_BUFFER_TYPE(CMSG_SPACE(sizeof(int) * BUS_FDS_MAX)) control;
+        bool handle_cmsg = false;
+
+        assert(b);
+        assert(b->state == BUS_AUTHENTICATING);
+
+        r = bus_socket_auth_verify(b);
+        if (r != 0)
+                return r;
+
+        n = MAX(256u, b->rbuffer_size * 2);
+
+        if (n > BUS_AUTH_SIZE_MAX)
+                n = BUS_AUTH_SIZE_MAX;
+
+        if (b->rbuffer_size >= n)
+                return -ENOBUFS;
+
+        p = realloc(b->rbuffer, n);
+        if (!p)
+                return -ENOMEM;
+
+        b->rbuffer = p;
+
+        iov = IOVEC_MAKE((uint8_t *)b->rbuffer + b->rbuffer_size, n - b->rbuffer_size);
+
+        if (b->prefer_readv) {
+                k = readv(b->input_fd, &iov, 1);
+                if (k < 0)
+                        k = -errno;
+        } else {
+                mh = (struct msghdr) {
+                        .msg_iov = &iov,
+                        .msg_iovlen = 1,
+                        .msg_control = &control,
+                        .msg_controllen = sizeof(control),
+                };
+
+                k = recvmsg_safe(b->input_fd, &mh, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
+                if (k == -ENOTSOCK) {
+                        b->prefer_readv = true;
+                        k = readv(b->input_fd, &iov, 1);
+                        if (k < 0)
+                                k = -errno;
+                } else
+                        handle_cmsg = true;
+        }
+        if (k == -EAGAIN)
+                return 0;
+        if (k < 0)
+                return (int) k;
+        if (k == 0) {
+                if (handle_cmsg)
+                        cmsg_close_all(&mh); /* paranoia, we shouldn't have gotten any fds on EOF */
+                return -ECONNRESET;
+        }
+
+        b->rbuffer_size += k;
+
+        if (handle_cmsg) {
+                struct cmsghdr *cmsg;
+
+                CMSG_FOREACH(cmsg, &mh)
+                        if (cmsg->cmsg_level == SOL_SOCKET &&
+                            cmsg->cmsg_type == SCM_RIGHTS) {
+                                int j;
+
+                                /* Whut? We received fds during the auth
+                                 * protocol? Somebody is playing games with
+                                 * us. Close them all, and fail */
+                                j = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+                                close_many((int*) CMSG_DATA(cmsg), j);
+                                return -EIO;
+                        } else
+                                log_debug("Got unexpected auxiliary data with level=%d and type=%d",
+                                          cmsg->cmsg_level, cmsg->cmsg_type);
+        }
+
+        r = bus_socket_auth_verify(b);
+        if (r != 0)
+                return r;
+
+        return 1;
+}
+
+void bus_socket_setup(sd_bus *b) {
+        assert(b);
+
+        /* Increase the buffers to 8 MB */
+        (void) fd_inc_rcvbuf(b->input_fd, SNDBUF_SIZE);
+        (void) fd_inc_sndbuf(b->output_fd, SNDBUF_SIZE);
+
+        b->message_version = 1;
+        b->message_endian = 0;
+}
+
+static void bus_get_peercred(sd_bus *b) {
+        int r;
+
+        assert(b);
+        assert(!b->ucred_valid);
+        assert(!b->label);
+        assert(b->n_groups == (size_t) -1);
+
+        /* Get the peer for socketpair() sockets */
+        b->ucred_valid = getpeercred(b->input_fd, &b->ucred) >= 0;
+
+        /* Get the SELinux context of the peer */
+        r = getpeersec(b->input_fd, &b->label);
+        if (r < 0 && !IN_SET(r, -EOPNOTSUPP, -ENOPROTOOPT))
+                log_debug_errno(r, "Failed to determine peer security context: %m");
+
+        /* Get the list of auxiliary groups of the peer */
+        r = getpeergroups(b->input_fd, &b->groups);
+        if (r >= 0)
+                b->n_groups = (size_t) r;
+        else if (!IN_SET(r, -EOPNOTSUPP, -ENOPROTOOPT))
+                log_debug_errno(r, "Failed to determine peer's group list: %m");
+}
+
+static int bus_socket_start_auth_client(sd_bus *b) {
+        static const char sasl_auth_anonymous[] = {
+                /*
+                 * We use an arbitrary trace-string for the ANONYMOUS authentication. It can be used by the
+                 * message broker to aid debugging of clients. We fully anonymize the connection and use a
+                 * static default.
+                 */
+                "\0AUTH ANONYMOUS\r\n"
+                /* HEX a n o n y m o u s */
+                "DATA 616e6f6e796d6f7573\r\n"
+        };
+        static const char sasl_auth_external[] = {
+                "\0AUTH EXTERNAL\r\n"
+                "DATA\r\n"
+        };
+        static const char sasl_negotiate_unix_fd[] = {
+                "NEGOTIATE_UNIX_FD\r\n"
+        };
+        static const char sasl_begin[] = {
+                "BEGIN\r\n"
+        };
+        size_t i = 0;
+
+        assert(b);
+
+        if (b->anonymous_auth)
+                b->auth_iovec[i++] = IOVEC_MAKE((char*) sasl_auth_anonymous, sizeof(sasl_auth_anonymous) - 1);
+        else
+                b->auth_iovec[i++] = IOVEC_MAKE((char*) sasl_auth_external, sizeof(sasl_auth_external) - 1);
+
+        if (b->accept_fd)
+                b->auth_iovec[i++] = IOVEC_MAKE_STRING(sasl_negotiate_unix_fd);
+
+        b->auth_iovec[i++] = IOVEC_MAKE_STRING(sasl_begin);
+
+        return bus_socket_write_auth(b);
+}
+
+int bus_socket_start_auth(sd_bus *b) {
+        assert(b);
+
+        bus_get_peercred(b);
+
+        bus_set_state(b, BUS_AUTHENTICATING);
+        b->auth_timeout = now(CLOCK_MONOTONIC) + BUS_AUTH_TIMEOUT;
+
+        if (sd_is_socket(b->input_fd, AF_UNIX, 0, 0) <= 0)
+                b->accept_fd = false;
+
+        if (b->output_fd != b->input_fd)
+                if (sd_is_socket(b->output_fd, AF_UNIX, 0, 0) <= 0)
+                        b->accept_fd = false;
+
+        if (b->is_server)
+                return bus_socket_read_auth(b);
+        else
+                return bus_socket_start_auth_client(b);
+}
+
+static int bus_socket_inotify_setup(sd_bus *b) {
+        _cleanup_free_ int *new_watches = NULL;
+        _cleanup_free_ char *absolute = NULL;
+        size_t n_allocated = 0, n = 0, done = 0, i;
+        unsigned max_follow = 32;
+        const char *p;
+        int wd, r;
+
+        assert(b);
+        assert(b->watch_bind);
+        assert(b->sockaddr.sa.sa_family == AF_UNIX);
+        assert(b->sockaddr.un.sun_path[0] != 0);
+
+        /* Sets up an inotify fd in case watch_bind is enabled: wait until the configured AF_UNIX file system socket
+         * appears before connecting to it. The implemented is pretty simplistic: we just subscribe to relevant changes
+         * to all prefix components of the path, and every time we get an event for that we try to reconnect again,
+         * without actually caring what precisely the event we got told us. If we still can't connect we re-subscribe
+         * to all relevant changes of anything in the path, so that our watches include any possibly newly created path
+         * components. */
+
+        if (b->inotify_fd < 0) {
+                b->inotify_fd = inotify_init1(IN_NONBLOCK|IN_CLOEXEC);
+                if (b->inotify_fd < 0)
+                        return -errno;
+
+                b->inotify_fd = fd_move_above_stdio(b->inotify_fd);
+        }
+
+        /* Make sure the path is NUL terminated */
+        p = strndupa(b->sockaddr.un.sun_path, sizeof(b->sockaddr.un.sun_path));
+
+        /* Make sure the path is absolute */
+        r = path_make_absolute_cwd(p, &absolute);
+        if (r < 0)
+                goto fail;
+
+        /* Watch all parent directories, and don't mind any prefix that doesn't exist yet. For the innermost directory
+         * that exists we want to know when files are created or moved into it. For all parents of it we just care if
+         * they are removed or renamed. */
+
+        if (!GREEDY_REALLOC(new_watches, n_allocated, n + 1)) {
+                r = -ENOMEM;
+                goto fail;
+        }
+
+        /* Start with the top-level directory, which is a bit simpler than the rest, since it can't be a symlink, and
+         * always exists */
+        wd = inotify_add_watch(b->inotify_fd, "/", IN_CREATE|IN_MOVED_TO);
+        if (wd < 0) {
+                r = log_debug_errno(errno, "Failed to add inotify watch on /: %m");
+                goto fail;
+        } else
+                new_watches[n++] = wd;
+
+        for (;;) {
+                _cleanup_free_ char *component = NULL, *prefix = NULL, *destination = NULL;
+                size_t n_slashes, n_component;
+                char *c = NULL;
+
+                n_slashes = strspn(absolute + done, "/");
+                n_component = n_slashes + strcspn(absolute + done + n_slashes, "/");
+
+                if (n_component == 0) /* The end */
+                        break;
+
+                component = strndup(absolute + done, n_component);
+                if (!component) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                /* A trailing slash? That's a directory, and not a socket then */
+                if (path_equal(component, "/")) {
+                        r = -EISDIR;
+                        goto fail;
+                }
+
+                /* A single dot? Let's eat this up */
+                if (path_equal(component, "/.")) {
+                        done += n_component;
+                        continue;
+                }
+
+                prefix = strndup(absolute, done + n_component);
+                if (!prefix) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                if (!GREEDY_REALLOC(new_watches, n_allocated, n + 1)) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                wd = inotify_add_watch(b->inotify_fd, prefix, IN_DELETE_SELF|IN_MOVE_SELF|IN_ATTRIB|IN_CREATE|IN_MOVED_TO|IN_DONT_FOLLOW);
+                log_debug("Added inotify watch for %s on bus %s: %i", prefix, strna(b->description), wd);
+
+                if (wd < 0) {
+                        if (IN_SET(errno, ENOENT, ELOOP))
+                                break; /* This component doesn't exist yet, or the path contains a cyclic symlink right now */
+
+                        r = log_debug_errno(errno, "Failed to add inotify watch on %s: %m", empty_to_root(prefix));
+                        goto fail;
+                } else
+                        new_watches[n++] = wd;
+
+                /* Check if this is possibly a symlink. If so, let's follow it and watch it too. */
+                r = readlink_malloc(prefix, &destination);
+                if (r == -EINVAL) { /* not a symlink */
+                        done += n_component;
+                        continue;
+                }
+                if (r < 0)
+                        goto fail;
+
+                if (isempty(destination)) { /* Empty symlink target? Yuck! */
+                        r = -EINVAL;
+                        goto fail;
+                }
+
+                if (max_follow <= 0) { /* Let's make sure we don't follow symlinks forever */
+                        r = -ELOOP;
+                        goto fail;
+                }
+
+                if (path_is_absolute(destination)) {
+                        /* For absolute symlinks we build the new path and start anew */
+                        c = strjoin(destination, absolute + done + n_component);
+                        done = 0;
+                } else {
+                        _cleanup_free_ char *t = NULL;
+
+                        /* For relative symlinks we replace the last component, and try again */
+                        t = strndup(absolute, done);
+                        if (!t)
+                                return -ENOMEM;
+
+                        c = strjoin(t, "/", destination, absolute + done + n_component);
+                }
+                if (!c) {
+                        r = -ENOMEM;
+                        goto fail;
+                }
+
+                free(absolute);
+                absolute = c;
+
+                max_follow--;
+        }
+
+        /* And now, let's remove all watches from the previous iteration we don't need anymore */
+        for (i = 0; i < b->n_inotify_watches; i++) {
+                bool found = false;
+                size_t j;
+
+                for (j = 0; j < n; j++)
+                        if (new_watches[j] == b->inotify_watches[i]) {
+                                found = true;
+                                break;
+                        }
+
+                if (found)
+                        continue;
+
+                (void) inotify_rm_watch(b->inotify_fd, b->inotify_watches[i]);
+        }
+
+        free_and_replace(b->inotify_watches, new_watches);
+        b->n_inotify_watches = n;
+
+        return 0;
+
+fail:
+        bus_close_inotify_fd(b);
+        return r;
+}
+
+int bus_socket_connect(sd_bus *b) {
+        bool inotify_done = false;
+        int r;
+
+        assert(b);
+
+        for (;;) {
+                assert(b->input_fd < 0);
+                assert(b->output_fd < 0);
+                assert(b->sockaddr.sa.sa_family != AF_UNSPEC);
+
+                if (DEBUG_LOGGING) {
+                        _cleanup_free_ char *pretty = NULL;
+                        (void) sockaddr_pretty(&b->sockaddr.sa, b->sockaddr_size, false, true, &pretty);
+                        log_debug("sd-bus: starting bus%s%s by connecting to %s...",
+                                  b->description ? " " : "", strempty(b->description), strnull(pretty));
+                }
+
+                b->input_fd = socket(b->sockaddr.sa.sa_family, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
+                if (b->input_fd < 0)
+                        return -errno;
+
+                b->input_fd = fd_move_above_stdio(b->input_fd);
+
+                b->output_fd = b->input_fd;
+                bus_socket_setup(b);
+
+                if (connect(b->input_fd, &b->sockaddr.sa, b->sockaddr_size) < 0) {
+                        if (errno == EINPROGRESS) {
+
+                                /* If we have any inotify watches open, close them now, we don't need them anymore, as
+                                 * we have successfully initiated a connection */
+                                bus_close_inotify_fd(b);
+
+                                /* Note that very likely we are already in BUS_OPENING state here, as we enter it when
+                                 * we start parsing the address string. The only reason we set the state explicitly
+                                 * here, is to undo BUS_WATCH_BIND, in case we did the inotify magic. */
+                                bus_set_state(b, BUS_OPENING);
+                                return 1;
+                        }
+
+                        if (IN_SET(errno, ENOENT, ECONNREFUSED) &&  /* ENOENT → unix socket doesn't exist at all; ECONNREFUSED → unix socket stale */
+                            b->watch_bind &&
+                            b->sockaddr.sa.sa_family == AF_UNIX &&
+                            b->sockaddr.un.sun_path[0] != 0) {
+
+                                /* This connection attempt failed, let's release the socket for now, and start with a
+                                 * fresh one when reconnecting. */
+                                bus_close_io_fds(b);
+
+                                if (inotify_done) {
+                                        /* inotify set up already, don't do it again, just return now, and remember
+                                         * that we are waiting for inotify events now. */
+                                        bus_set_state(b, BUS_WATCH_BIND);
+                                        return 1;
+                                }
+
+                                /* This is a file system socket, and the inotify logic is enabled. Let's create the necessary inotify fd. */
+                                r = bus_socket_inotify_setup(b);
+                                if (r < 0)
+                                        return r;
+
+                                /* Let's now try to connect a second time, because in theory there's otherwise a race
+                                 * here: the socket might have been created in the time between our first connect() and
+                                 * the time we set up the inotify logic. But let's remember that we set up inotify now,
+                                 * so that we don't do the connect() more than twice. */
+                                inotify_done = true;
+
+                        } else
+                                return -errno;
+                } else
+                        break;
+        }
+
+        /* Yay, established, we don't need no inotify anymore! */
+        bus_close_inotify_fd(b);
+
+        return bus_socket_start_auth(b);
+}
+
+int bus_socket_exec(sd_bus *b) {
+        int s[2], r;
+
+        assert(b);
+        assert(b->input_fd < 0);
+        assert(b->output_fd < 0);
+        assert(b->exec_path);
+        assert(b->busexec_pid == 0);
+
+        log_debug("sd-bus: starting bus%s%s with %s...",
+                  b->description ? " " : "", strempty(b->description), b->exec_path);
+
+        r = socketpair(AF_UNIX, SOCK_STREAM|SOCK_NONBLOCK|SOCK_CLOEXEC, 0, s);
+        if (r < 0)
+                return -errno;
+
+        r = safe_fork_full("(sd-busexec)", s+1, 1, FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS, &b->busexec_pid);
+        if (r < 0) {
+                safe_close_pair(s);
+                return r;
+        }
+        if (r == 0) {
+                /* Child */
+
+                if (rearrange_stdio(s[1], s[1], STDERR_FILENO) < 0)
+                        _exit(EXIT_FAILURE);
+
+                (void) rlimit_nofile_safe();
+
+                if (b->exec_argv)
+                        execvp(b->exec_path, b->exec_argv);
+                else {
+                        const char *argv[] = { b->exec_path, NULL };
+                        execvp(b->exec_path, (char**) argv);
+                }
+
+                _exit(EXIT_FAILURE);
+        }
+
+        safe_close(s[1]);
+        b->output_fd = b->input_fd = fd_move_above_stdio(s[0]);
+
+        bus_socket_setup(b);
+
+        return bus_socket_start_auth(b);
+}
+
+int bus_socket_take_fd(sd_bus *b) {
+        assert(b);
+
+        bus_socket_setup(b);
+
+        return bus_socket_start_auth(b);
+}
+
+int bus_socket_write_message(sd_bus *bus, sd_bus_message *m, size_t *idx) {
+        struct iovec *iov;
+        ssize_t k;
+        size_t n;
+        unsigned j;
+        int r;
+
+        assert(bus);
+        assert(m);
+        assert(idx);
+        assert(IN_SET(bus->state, BUS_RUNNING, BUS_HELLO));
+
+        if (*idx >= BUS_MESSAGE_SIZE(m))
+                return 0;
+
+        r = bus_message_setup_iovec(m);
+        if (r < 0)
+                return r;
+
+        n = m->n_iovec * sizeof(struct iovec);
+        iov = newa(struct iovec, n);
+        memcpy_safe(iov, m->iovec, n);
+
+        j = 0;
+        iovec_advance(iov, &j, *idx);
+
+        if (bus->prefer_writev)
+                k = writev(bus->output_fd, iov, m->n_iovec);
+        else {
+                struct msghdr mh = {
+                        .msg_iov = iov,
+                        .msg_iovlen = m->n_iovec,
+                };
+
+                if (m->n_fds > 0 && *idx == 0) {
+                        struct cmsghdr *control;
+
+                        mh.msg_controllen = CMSG_SPACE(sizeof(int) * m->n_fds);
+                        mh.msg_control = alloca0(mh.msg_controllen);
+                        control = CMSG_FIRSTHDR(&mh);
+                        control->cmsg_len = CMSG_LEN(sizeof(int) * m->n_fds);
+                        control->cmsg_level = SOL_SOCKET;
+                        control->cmsg_type = SCM_RIGHTS;
+                        memcpy(CMSG_DATA(control), m->fds, sizeof(int) * m->n_fds);
+                }
+
+                k = sendmsg(bus->output_fd, &mh, MSG_DONTWAIT|MSG_NOSIGNAL);
+                if (k < 0 && errno == ENOTSOCK) {
+                        bus->prefer_writev = true;
+                        k = writev(bus->output_fd, iov, m->n_iovec);
+                }
+        }
+
+        if (k < 0)
+                return errno == EAGAIN ? 0 : -errno;
+
+        *idx += (size_t) k;
+        return 1;
+}
+
+static int bus_socket_read_message_need(sd_bus *bus, size_t *need) {
+        uint32_t a, b;
+        uint8_t e;
+        uint64_t sum;
+
+        assert(bus);
+        assert(need);
+        assert(IN_SET(bus->state, BUS_RUNNING, BUS_HELLO));
+
+        if (bus->rbuffer_size < sizeof(struct bus_header)) {
+                *need = sizeof(struct bus_header) + 8;
+
+                /* Minimum message size:
+                 *
+                 * Header +
+                 *
+                 *  Method Call: +2 string headers
+                 *       Signal: +3 string headers
+                 * Method Error: +1 string headers
+                 *               +1 uint32 headers
+                 * Method Reply: +1 uint32 headers
+                 *
+                 * A string header is at least 9 bytes
+                 * A uint32 header is at least 8 bytes
+                 *
+                 * Hence the minimum message size of a valid message
+                 * is header + 8 bytes */
+
+                return 0;
+        }
+
+        a = ((const uint32_t*) bus->rbuffer)[1];
+        b = ((const uint32_t*) bus->rbuffer)[3];
+
+        e = ((const uint8_t*) bus->rbuffer)[0];
+        if (e == BUS_LITTLE_ENDIAN) {
+                a = le32toh(a);
+                b = le32toh(b);
+        } else if (e == BUS_BIG_ENDIAN) {
+                a = be32toh(a);
+                b = be32toh(b);
+        } else
+                return -EBADMSG;
+
+        sum = (uint64_t) sizeof(struct bus_header) + (uint64_t) ALIGN_TO(b, 8) + (uint64_t) a;
+        if (sum >= BUS_MESSAGE_SIZE_MAX)
+                return -ENOBUFS;
+
+        *need = (size_t) sum;
+        return 0;
+}
+
+static int bus_socket_make_message(sd_bus *bus, size_t size) {
+        sd_bus_message *t = NULL;
+        void *b;
+        int r;
+
+        assert(bus);
+        assert(bus->rbuffer_size >= size);
+        assert(IN_SET(bus->state, BUS_RUNNING, BUS_HELLO));
+
+        r = bus_rqueue_make_room(bus);
+        if (r < 0)
+                return r;
+
+        if (bus->rbuffer_size > size) {
+                b = memdup((const uint8_t*) bus->rbuffer + size,
+                           bus->rbuffer_size - size);
+                if (!b)
+                        return -ENOMEM;
+        } else
+                b = NULL;
+
+        r = bus_message_from_malloc(bus,
+                                    bus->rbuffer, size,
+                                    bus->fds, bus->n_fds,
+                                    NULL,
+                                    &t);
+        if (r == -EBADMSG) {
+                log_debug_errno(r, "Received invalid message from connection %s, dropping.", strna(bus->description));
+                free(bus->rbuffer); /* We want to drop current rbuffer and proceed with whatever remains in b */
+        } else if (r < 0) {
+                free(b);
+                return r;
+        }
+
+        /* rbuffer ownership was either transferred to t, or we got EBADMSG and dropped it. */
+        bus->rbuffer = b;
+        bus->rbuffer_size -= size;
+
+        bus->fds = NULL;
+        bus->n_fds = 0;
+
+        if (t) {
+                t->read_counter = ++bus->read_counter;
+                bus->rqueue[bus->rqueue_size++] = bus_message_ref_queued(t, bus);
+                sd_bus_message_unref(t);
+        }
+
+        return 1;
+}
+
+int bus_socket_read_message(sd_bus *bus) {
+        struct msghdr mh;
+        struct iovec iov = {};
+        ssize_t k;
+        size_t need;
+        int r;
+        void *b;
+        CMSG_BUFFER_TYPE(CMSG_SPACE(sizeof(int) * BUS_FDS_MAX)) control;
+        bool handle_cmsg = false;
+
+        assert(bus);
+        assert(IN_SET(bus->state, BUS_RUNNING, BUS_HELLO));
+
+        r = bus_socket_read_message_need(bus, &need);
+        if (r < 0)
+                return r;
+
+        if (bus->rbuffer_size >= need)
+                return bus_socket_make_message(bus, need);
+
+        b = realloc(bus->rbuffer, need);
+        if (!b)
+                return -ENOMEM;
+
+        bus->rbuffer = b;
+
+        iov = IOVEC_MAKE((uint8_t *)bus->rbuffer + bus->rbuffer_size, need - bus->rbuffer_size);
+
+        if (bus->prefer_readv) {
+                k = readv(bus->input_fd, &iov, 1);
+                if (k < 0)
+                        k = -errno;
+        } else {
+                mh = (struct msghdr) {
+                        .msg_iov = &iov,
+                        .msg_iovlen = 1,
+                        .msg_control = &control,
+                        .msg_controllen = sizeof(control),
+                };
+
+                k = recvmsg_safe(bus->input_fd, &mh, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
+                if (k == -ENOTSOCK) {
+                        bus->prefer_readv = true;
+                        k = readv(bus->input_fd, &iov, 1);
+                        if (k < 0)
+                                k = -errno;
+                } else
+                        handle_cmsg = true;
+        }
+        if (k == -EAGAIN)
+                return 0;
+        if (k < 0)
+                return (int) k;
+        if (k == 0) {
+                if (handle_cmsg)
+                        cmsg_close_all(&mh); /* On EOF we shouldn't have gotten an fd, but let's make sure */
+                return -ECONNRESET;
+        }
+
+        bus->rbuffer_size += k;
+
+        if (handle_cmsg) {
+                struct cmsghdr *cmsg;
+
+                CMSG_FOREACH(cmsg, &mh)
+                        if (cmsg->cmsg_level == SOL_SOCKET &&
+                            cmsg->cmsg_type == SCM_RIGHTS) {
+                                int n, *f, i;
+
+                                n = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+
+                                if (!bus->can_fds) {
+                                        /* Whut? We received fds but this
+                                         * isn't actually enabled? Close them,
+                                         * and fail */
+
+                                        close_many((int*) CMSG_DATA(cmsg), n);
+                                        return -EIO;
+                                }
+
+                                f = reallocarray(bus->fds, bus->n_fds + n, sizeof(int));
+                                if (!f) {
+                                        close_many((int*) CMSG_DATA(cmsg), n);
+                                        return -ENOMEM;
+                                }
+
+                                for (i = 0; i < n; i++)
+                                        f[bus->n_fds++] = fd_move_above_stdio(((int*) CMSG_DATA(cmsg))[i]);
+                                bus->fds = f;
+                        } else
+                                log_debug("Got unexpected auxiliary data with level=%d and type=%d",
+                                          cmsg->cmsg_level, cmsg->cmsg_type);
+        }
+
+        r = bus_socket_read_message_need(bus, &need);
+        if (r < 0)
+                return r;
+
+        if (bus->rbuffer_size >= need)
+                return bus_socket_make_message(bus, need);
+
+        return 1;
+}
+
+int bus_socket_process_opening(sd_bus *b) {
+        int error = 0, events, r;
+        socklen_t slen = sizeof(error);
+
+        assert(b->state == BUS_OPENING);
+
+        events = fd_wait_for_event(b->output_fd, POLLOUT, 0);
+        if (events < 0)
+                return events;
+        if (!(events & (POLLOUT|POLLERR|POLLHUP)))
+                return 0;
+
+        r = getsockopt(b->output_fd, SOL_SOCKET, SO_ERROR, &error, &slen);
+        if (r < 0)
+                b->last_connect_error = errno;
+        else if (error != 0)
+                b->last_connect_error = error;
+        else if (events & (POLLERR|POLLHUP))
+                b->last_connect_error = ECONNREFUSED;
+        else
+                return bus_socket_start_auth(b);
+
+        return bus_next_address(b);
+}
+
+int bus_socket_process_authenticating(sd_bus *b) {
+        int r;
+
+        assert(b);
+        assert(b->state == BUS_AUTHENTICATING);
+
+        if (now(CLOCK_MONOTONIC) >= b->auth_timeout)
+                return -ETIMEDOUT;
+
+        r = bus_socket_write_auth(b);
+        if (r != 0)
+                return r;
+
+        return bus_socket_read_auth(b);
+}
+
+int bus_socket_process_watch_bind(sd_bus *b) {
+        int r, q;
+
+        assert(b);
+        assert(b->state == BUS_WATCH_BIND);
+        assert(b->inotify_fd >= 0);
+
+        r = flush_fd(b->inotify_fd);
+        if (r <= 0)
+                return r;
+
+        log_debug("Got inotify event on bus %s.", strna(b->description));
+
+        /* We flushed events out of the inotify fd. In that case, maybe the socket is valid now? Let's try to connect
+         * to it again */
+
+        r = bus_socket_connect(b);
+        if (r < 0)
+                return r;
+
+        q = bus_attach_io_events(b);
+        if (q < 0)
+                return q;
+
+        q = bus_attach_inotify_event(b);
+        if (q < 0)
+                return q;
+
+        return r;
+}