sd-bus: use the new information in the client's sockaddr in the creds structure

Now that clients might convey comm/description strings via the sockaddr,
let's actually use them on the other side, read the data via
getpeername() parse it, and include it in the "owner" creds (which is
how we call the peer's creds).

src/libsystemd/sd-bus/bus-control.c

@@ -722,9 +722,51 @@ _public_ int sd_bus_get_name_creds(
         return 0;
 }
 
+static int parse_sockaddr_string(const char *t, char **ret_comm, char **ret_description) {
+        _cleanup_free_ char *comm = NULL, *description = NULL;
+        const char *e, *sl;
+
+        assert(t);
+        assert(ret_comm);
+        assert(ret_description);
+
+        e = strstrafter(t, "/bus/");
+        if (!e) {
+                log_debug("Didn't find /bus/ substring in peer socket address, ignoring.");
+                goto not_found;
+        }
+
+        sl = strchr(e, '/');
+        if (!sl) {
+                log_debug("Didn't find / substring after /bus/ in peer socket address, ignoring.");
+                goto not_found;
+        }
+
+        if (sl - e > 0) {
+                comm = strndup(e, sl - e);
+                if (!comm)
+                        return -ENOMEM;
+        }
+
+        sl++;
+        if (!isempty(sl)) {
+                description = strdup(sl);
+                if (!description)
+                        return -ENOMEM;
+        }
+
+        *ret_comm = TAKE_PTR(comm);
+        *ret_description = TAKE_PTR(description);
+        return 0;
+
+not_found:
+        *ret_comm = *ret_description = NULL;
+        return 0;
+}
+
 _public_ int sd_bus_get_owner_creds(sd_bus *bus, uint64_t mask, sd_bus_creds **ret) {
         _cleanup_(sd_bus_creds_unrefp) sd_bus_creds *c = NULL;
-        bool do_label, do_groups;
+        bool do_label, do_groups, do_sockaddr_peer;
         pid_t pid = 0;
         int r;
 
@@ -742,9 +784,12 @@ _public_ int sd_bus_get_owner_creds(sd_bus *bus, uint64_t mask, sd_bus_creds **r
 
         do_label = bus->label && (mask & SD_BUS_CREDS_SELINUX_CONTEXT);
         do_groups = bus->n_groups != SIZE_MAX && (mask & SD_BUS_CREDS_SUPPLEMENTARY_GIDS);
+        do_sockaddr_peer = bus->sockaddr_size_peer >= offsetof(struct sockaddr_un, sun_path) + 1 &&
+                bus->sockaddr_peer.sa.sa_family == AF_UNIX &&
+                bus->sockaddr_peer.un.sun_path[0] == 0;
 
         /* Avoid allocating anything if we have no chance of returning useful data */
-        if (!bus->ucred_valid && !do_label && !do_groups)
+        if (!bus->ucred_valid && !do_label && !do_groups && !do_sockaddr_peer)
                 return -ENODATA;
 
         c = bus_creds_new();
@@ -786,6 +831,35 @@ _public_ int sd_bus_get_owner_creds(sd_bus *bus, uint64_t mask, sd_bus_creds **r
                 c->mask |= SD_BUS_CREDS_SUPPLEMENTARY_GIDS;
         }
 
+        if (do_sockaddr_peer) {
+                _cleanup_free_ char *t = NULL;
+
+                assert(bus->sockaddr_size_peer >= offsetof(struct sockaddr_un, sun_path) + 1);
+                assert(bus->sockaddr_peer.sa.sa_family == AF_UNIX);
+                assert(bus->sockaddr_peer.un.sun_path[0] == 0);
+
+                /* So this is an abstract namespace socket, good. Now let's find the data we are interested in */
+                r = make_cstring(bus->sockaddr_peer.un.sun_path + 1,
+                                 bus->sockaddr_size_peer - offsetof(struct sockaddr_un, sun_path) - 1,
+                                 MAKE_CSTRING_ALLOW_TRAILING_NUL,
+                                 &t);
+                if (r == -ENOMEM)
+                        return r;
+                if (r < 0)
+                        log_debug_errno(r, "Can't extract string from peer socket address, ignoring: %m");
+                else {
+                        r = parse_sockaddr_string(t, &c->comm, &c->description);
+                        if (r < 0)
+                                return r;
+
+                        if (c->comm)
+                                c->mask |= SD_BUS_CREDS_COMM & mask;
+
+                        if (c->description)
+                                c->mask |= SD_BUS_CREDS_DESCRIPTION & mask;
+                }
+        }
+
         r = bus_creds_add_more(c, mask, pid, 0);
         if (r < 0 && r != -ESRCH) /* If the process vanished, then don't complain, just return what we got */
                 return r;

src/libsystemd/sd-bus/bus-internal.h

@@ -267,6 +267,8 @@ struct sd_bus {
         char *label;
         gid_t *groups;
         size_t n_groups;
+        union sockaddr_union sockaddr_peer;
+        socklen_t sockaddr_size_peer;
 
         uint64_t creds_mask;
 

src/libsystemd/sd-bus/bus-socket.c

@@ -652,6 +652,17 @@ static void bus_get_peercred(sd_bus *b) {
                 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");
+
+        /* Let's query the peers socket address, it might carry information such as the peer's comm or
+         * description string */
+        zero(b->sockaddr_peer);
+        b->sockaddr_size_peer = 0;
+
+        socklen_t l = sizeof(b->sockaddr_peer) - 1; /* Leave space for a NUL */
+        if (getpeername(b->input_fd, &b->sockaddr_peer.sa, &l) < 0)
+                log_debug_errno(errno, "Failed to get peer's socket address, ignoring: %m");
+        else
+                b->sockaddr_size_peer = l;
 }
 
 static int bus_socket_start_auth_client(sd_bus *b) {