Implement SocketUser= and SocketGroup= for [Socket]

Since we already allow defining the mode of AF_UNIX sockets and FIFO, it
makes sense to also allow specific user/group ownership of the socket
file for restricting access.

6 files changed, 97 insertions, 3 deletions

diff --git a/man/systemd.socket.xml b/man/systemd.socket.xml
index 4b1fcc8b0c..dc0d78f0a2 100644
--- a/man/systemd.socket.xml
+++ b/man/systemd.socket.xml
@@ -358,6 +358,30 @@
                         </varlistentry>
 
                         <varlistentry>
+                                <term><varname>SocketUser=</varname></term>
+                                <listitem><para>If listening on a file system
+                                socket or FIFO, this option specifies the
+                                user owner of the created socket. When
+                                defining this, keep in mind that name
+                                switch services for user name lookups may
+                                not be available. It is advisable to use a
+                                numeric UID for this
+                                setting.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>SocketGroup=</varname></term>
+                                <listitem><para>If listening on a file system
+                                socket or FIFO, this option specifies the
+                                group owner of the created socket. When
+                                defining this, keep in mind that name
+                                switch services for group name lookups may
+                                not be available. It is advisable to use a
+                                numeric GID for this
+                                setting.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
                                 <term><varname>Accept=</varname></term>
                                 <listitem><para>Takes a boolean
                                 argument. If true, a service instance
diff --git a/src/core/dbus-socket.c b/src/core/dbus-socket.c
index 095a031612..887c80eb89 100644
--- a/src/core/dbus-socket.c
+++ b/src/core/dbus-socket.c
@@ -43,6 +43,8 @@
         "  <property name=\"BindToDevice\" type=\"s\" access=\"read\"/>\n" \
         "  <property name=\"DirectoryMode\" type=\"u\" access=\"read\"/>\n" \
         "  <property name=\"SocketMode\" type=\"u\" access=\"read\"/>\n" \
+        "  <property name=\"SocketUser\" type=\"s\" access=\"read\"/>\n" \
+        "  <property name=\"SocketGroup\" type=\"s\" access=\"read\"/>\n" \
         "  <property name=\"Accept\" type=\"b\" access=\"read\"/>\n"    \
         "  <property name=\"KeepAlive\" type=\"b\" access=\"read\"/>\n" \
         "  <property name=\"Priority\" type=\"i\" access=\"read\"/>\n"  \
@@ -109,6 +111,8 @@ static const BusProperty bus_socket_properties[] = {
         { "BindToDevice",   bus_property_append_string,        "s", offsetof(Socket, bind_to_device), true },
         { "DirectoryMode",  bus_property_append_mode,          "u", offsetof(Socket, directory_mode)  },
         { "SocketMode",     bus_property_append_mode,          "u", offsetof(Socket, socket_mode)     },
+        { "SocketUser",     bus_property_append_string,        "s", offsetof(Socket, socket_user),    true },
+        { "SocketGroup",    bus_property_append_string,        "s", offsetof(Socket, socket_group),   true },
         { "Accept",         bus_property_append_bool,          "b", offsetof(Socket, accept)          },
         { "KeepAlive",      bus_property_append_bool,          "b", offsetof(Socket, keep_alive)      },
         { "Priority",       bus_property_append_int,           "i", offsetof(Socket, priority)        },
diff --git a/src/core/load-fragment-gperf.gperf.m4 b/src/core/load-fragment-gperf.gperf.m4
index 0c5ccebd73..b48e9e9f56 100644
--- a/src/core/load-fragment-gperf.gperf.m4
+++ b/src/core/load-fragment-gperf.gperf.m4
@@ -189,6 +189,8 @@ Socket.ExecStopPost,             config_parse_exec,                  SOCKET_EXEC
 Socket.TimeoutSec,               config_parse_usec,                  0,                             offsetof(Socket, timeout_usec)
 Socket.DirectoryMode,            config_parse_mode,                  0,                             offsetof(Socket, directory_mode)
 Socket.SocketMode,               config_parse_mode,                  0,                             offsetof(Socket, socket_mode)
+Socket.SocketUser,               config_parse_string,                0,                             offsetof(Socket, socket_user)
+Socket.SocketGroup,              config_parse_string,                0,                             offsetof(Socket, socket_group)
 Socket.Accept,                   config_parse_bool,                  0,                             offsetof(Socket, accept)
 Socket.MaxConnections,           config_parse_unsigned,              0,                             offsetof(Socket, max_connections)
 Socket.KeepAlive,                config_parse_bool,                  0,                             offsetof(Socket, keep_alive)
diff --git a/src/core/socket.c b/src/core/socket.c
index c0959815c1..f3f09cac43 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -136,6 +136,12 @@ static void socket_done(Unit *u) {
         free(s->smack_ip_in);
         free(s->smack_ip_out);
 
+        free(s->socket_user);
+        s->socket_user = NULL;
+
+        free(s->socket_group);
+        s->socket_group = NULL;
+
         unit_unwatch_timer(u, &s->timer_watch);
 }
 
@@ -449,6 +455,16 @@ static void socket_dump(Unit *u, FILE *f, const char *prefix) {
                 prefix, yes_no(s->pass_sec),
                 prefix, strna(s->tcp_congestion));
 
+        if (s->socket_user)
+                fprintf(f,
+                        "SocketUser: %s\n",
+                        s->socket_user);
+
+        if (s->socket_group)
+                fprintf(f,
+                        "SocketGroup: %s\n",
+                        s->socket_group);
+
         if (s->control_pid > 0)
                 fprintf(f,
                         "%sControl PID: %lu\n",
@@ -692,6 +708,9 @@ static void socket_close_fds(Socket *s) {
 }
 
 static void socket_apply_socket_options(Socket *s, int fd) {
+        uid_t uid = 0;
+        gid_t gid = 0;
+
         assert(s);
         assert(fd >= 0);
 
@@ -775,6 +794,21 @@ static void socket_apply_socket_options(Socket *s, int fd) {
         if (s->smack_ip_out)
                 if (fsetxattr(fd, "security.SMACK64IPOUT", s->smack_ip_out, strlen(s->smack_ip_out), 0) < 0)
                         log_error("fsetxattr(\"security.SMACK64IPOUT\"): %m");
+
+        if (s->socket_user &&
+            get_user_creds((const char **)&s->socket_user, &uid,
+                                NULL, NULL, NULL) < 0) {
+                log_warning("failed to lookup user: %s", s->socket_user);
+        }
+
+        if (s->socket_group &&
+            get_group_creds((const char **)&s->socket_group, &gid) < 0) {
+                log_warning("failed to lookup group: %s", s->socket_group);
+        }
+
+        if ((uid != 0 || gid != 0) && fchown(fd, uid, gid) < 0) {
+                log_warning("failed to change ownership of socket");
+        }
 }
 
 static void socket_apply_fifo_options(Socket *s, int fd) {
@@ -794,11 +828,15 @@ static int fifo_address_create(
                 const char *path,
                 mode_t directory_mode,
                 mode_t socket_mode,
+                const char *socket_user,
+                const char *socket_group,
                 int *_fd) {
 
         int fd = -1, r = 0;
         struct stat st;
         mode_t old_mask;
+        uid_t uid = 0;
+        gid_t gid = 0;
 
         assert(path);
         assert(_fd);
@@ -823,7 +861,8 @@ static int fifo_address_create(
                 goto fail;
         }
 
-        if ((fd = open(path, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW)) < 0) {
+        fd = open(path, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK|O_NOFOLLOW);
+        if (fd < 0) {
                 r = -errno;
                 goto fail;
         }
@@ -835,15 +874,35 @@ static int fifo_address_create(
                 goto fail;
         }
 
+        if (socket_user &&
+            get_user_creds(&socket_user, &uid, NULL, NULL, NULL) < 0) {
+                r = -errno;
+                log_error("failed to lookup user: %s", socket_user);
+                goto fail;
+        }
+
+        if (socket_group &&
+            get_group_creds(&socket_group, &gid) < 0) {
+                r = -errno;
+                log_error("failed to lookup group: %s", socket_group);
+                goto fail;
+        }
+
         if (!S_ISFIFO(st.st_mode) ||
             (st.st_mode & 0777) != (socket_mode & ~old_mask) ||
-            st.st_uid != getuid() ||
-            st.st_gid != getgid()) {
+            st.st_uid != uid ||
+            st.st_gid != gid) {
 
                 r = -EEXIST;
                 goto fail;
         }
 
+        if ((uid != 0 || gid != 0) && fchown(fd, uid, gid) < 0) {
+                r = -errno;
+                log_error("failed to changed ownership of FIFO: %s", path);
+                goto fail;
+        }
+
         *_fd = fd;
         return 0;
 
@@ -1013,6 +1072,8 @@ static int socket_open_fds(Socket *s) {
                                              p->path,
                                              s->directory_mode,
                                              s->socket_mode,
+                                             s->socket_user,
+                                             s->socket_group,
                                              &p->fd)) < 0)
                                 goto rollback;
 
diff --git a/src/core/socket.h b/src/core/socket.h
index f099520dce..a273ac2740 100644
--- a/src/core/socket.h
+++ b/src/core/socket.h
@@ -118,6 +118,8 @@ struct Socket {
 
         mode_t directory_mode;
         mode_t socket_mode;
+        char *socket_user;
+        char *socket_group;
 
         SocketResult result;
 
diff --git a/src/shared/socket-label.c b/src/shared/socket-label.c
index ff212de825..d105a66fe8 100644
--- a/src/shared/socket-label.c
+++ b/src/shared/socket-label.c
@@ -52,6 +52,7 @@ int socket_address_listen(
                 int *ret) {
 
         int r, fd, one;
+
         assert(a);
         assert(ret);