tree-wide: introduce new SOCKADDR_UN_LEN() macro, and use it everywhere

The macro determines the right length of a AF_UNIX "struct sockaddr_un" to pass to
connect() or bind(). It automatically figures out if the socket refers to an
abstract namespace socket, or a socket in the file system, and properly handles
the full length of the path field.

This macro is not only safer, but also simpler to use, than the usual
offsetof() + strlen() logic.

5 files changed, 17 insertions, 8 deletions

diff --git a/src/basic/log.c b/src/basic/log.c
index ca12c8b41..08aa986a0 100644
--- a/src/basic/log.c
+++ b/src/basic/log.c
@@ -165,7 +165,7 @@ static int log_open_syslog(void) {
                 goto fail;
         }
 
-        if (connect(syslog_fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(sa.un.sun_path)) < 0) {
+        if (connect(syslog_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                 safe_close(syslog_fd);
 
                 /* Some legacy syslog systems still use stream
@@ -177,7 +177,7 @@ static int log_open_syslog(void) {
                         goto fail;
                 }
 
-                if (connect(syslog_fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(sa.un.sun_path)) < 0) {
+                if (connect(syslog_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                         r = -errno;
                         goto fail;
                 }
@@ -216,7 +216,7 @@ static int log_open_journal(void) {
                 goto fail;
         }
 
-        if (connect(journal_fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(sa.un.sun_path)) < 0) {
+        if (connect(journal_fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0) {
                 r = -errno;
                 goto fail;
         }
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 449273d9a..8850d9f16 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -143,3 +143,14 @@ int receive_one_fd(int transport_fd, int flags);
 
 #define CMSG_FOREACH(cmsg, mh)                                          \
         for ((cmsg) = CMSG_FIRSTHDR(mh); (cmsg); (cmsg) = CMSG_NXTHDR((mh), (cmsg)))
+
+/* Covers only file system and abstract AF_UNIX socket addresses, but not unnamed socket addresses. */
+#define SOCKADDR_UN_LEN(sa)                                             \
+        ({                                                              \
+                const struct sockaddr_un *_sa = &(sa);                  \
+                assert(_sa->sun_family == AF_UNIX);                     \
+                offsetof(struct sockaddr_un, sun_path) +                \
+                        (_sa->sun_path[0] == 0 ?                        \
+                         1 + strnlen(_sa->sun_path+1, sizeof(_sa->sun_path)-1) : \
+                         strnlen(_sa->sun_path, sizeof(_sa->sun_path))); \
+        })
diff --git a/src/libelogind/sd-bus/sd-bus.c b/src/libelogind/sd-bus/sd-bus.c
index 6d304719e..8a5cd38f7 100644
--- a/src/libelogind/sd-bus/sd-bus.c
+++ b/src/libelogind/sd-bus/sd-bus.c
@@ -842,7 +842,7 @@ static int parse_container_unix_address(sd_bus *b, const char **p, char **guid)
 
         b->sockaddr.un.sun_family = AF_UNIX;
         strncpy(b->sockaddr.un.sun_path, "/var/run/dbus/system_bus_socket", sizeof(b->sockaddr.un.sun_path));
-        b->sockaddr_size = offsetof(struct sockaddr_un, sun_path) + strlen("/var/run/dbus/system_bus_socket");
+        b->sockaddr_size = SOCKADDR_UN_LEN(b->sockaddr.un);
 
         return 0;
 }
diff --git a/src/libelogind/sd-daemon/sd-daemon.c b/src/libelogind/sd-daemon/sd-daemon.c
index 773112249..44816401e 100644
--- a/src/libelogind/sd-daemon/sd-daemon.c
+++ b/src/libelogind/sd-daemon/sd-daemon.c
@@ -462,9 +462,7 @@ _public_ int sd_pid_notify_with_fds(pid_t pid, int unset_environment, const char
         if (sockaddr.un.sun_path[0] == '@')
                 sockaddr.un.sun_path[0] = 0;
 
-        msghdr.msg_namelen = offsetof(struct sockaddr_un, sun_path) + strlen(e);
-        if (msghdr.msg_namelen > sizeof(struct sockaddr_un))
-                msghdr.msg_namelen = sizeof(struct sockaddr_un);
+        msghdr.msg_namelen = SOCKADDR_UN_LEN(sockaddr.un);
 
         have_pid = pid != 0 && pid != getpid();
 
diff --git a/src/login/pam_elogind.c b/src/login/pam_elogind.c
index 40e246bb0..98dc20134 100644
--- a/src/login/pam_elogind.c
+++ b/src/login/pam_elogind.c
@@ -150,7 +150,7 @@ static int get_seat_from_display(const char *display, const char **seat, uint32_
         if (fd < 0)
                 return -errno;
 
-        if (connect(fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(sa.un.sun_path)) < 0)
+        if (connect(fd, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0)
                 return -errno;
 
         r = getpeercred(fd, &ucred);