Replace mkostemp+unlink with open(O_TMPFILE)

This will only work on Linux >= 3.11, and probably not on all
filesystems. Fallback code is provided.

src/core/manager.c

@@ -2005,28 +2005,17 @@ void manager_dispatch_bus_name_owner_changed(
 }
 
 int manager_open_serialization(Manager *m, FILE **_f) {
-        _cleanup_free_ char *path = NULL;
+        const char *path;
         int fd = -1;
         FILE *f;
 
         assert(_f);
 
-        if (m->running_as == SYSTEMD_SYSTEM)
-                asprintf(&path, "/run/systemd/dump-"PID_FMT"-XXXXXX", getpid());
-        else
-                asprintf(&path, "/tmp/systemd-dump-"PID_FMT"-XXXXXX", getpid());
-
-        if (!path)
-                return -ENOMEM;
-
-        RUN_WITH_UMASK(0077) {
-                fd = mkostemp(path, O_RDWR|O_CLOEXEC);
-        }
-
+        path = m->running_as == SYSTEMD_SYSTEM ? "/run/systemd" : "/tmp";
+        fd = open_tmpfile(path, O_RDWR|O_CLOEXEC);
         if (fd < 0)
                 return -errno;
 
-        unlink(path);
         log_debug("Serializing state to %s", path);
 
         f = fdopen(fd, "w+");

src/journal/journal-send.c

@@ -216,10 +216,6 @@ _public_ int sd_journal_sendv(const struct iovec *iov, int n) {
                 uint8_t buf[CMSG_SPACE(sizeof(int))];
         } control;
         struct cmsghdr *cmsg;
-        /* We use /dev/shm instead of /tmp here, since we want this to
-         * be a tmpfs, and one that is available from early boot on
-         * and where unprivileged users can create files. */
-        char path[] = "/dev/shm/journal.XXXXXX";
         bool have_syslog_identifier = false;
 
         assert_return(iov, -EINVAL);
@@ -309,16 +305,14 @@ _public_ int sd_journal_sendv(const struct iovec *iov, int n) {
 
         /* Message doesn't fit... Let's dump the data in a temporary
          * file and just pass a file descriptor of it to the other
-         * side */
-
-        buffer_fd = mkostemp(path, O_CLOEXEC|O_RDWR);
+         * side.
+         *
+         * We use /dev/shm instead of /tmp here, since we want this to
+         * be a tmpfs, and one that is available from early boot on
+         * and where unprivileged users can create files. */
+        buffer_fd = open_tmpfile("/dev/shm", O_RDWR | O_CLOEXEC);
         if (buffer_fd < 0)
-                return -errno;
-
-        if (unlink(path) < 0) {
-                close_nointr_nofail(buffer_fd);
-                return -errno;
-        }
+                return buffer_fd;
 
         n = writev(buffer_fd, w, j);
         if (n < 0) {

src/journal/journal-verify.c

@@ -785,9 +785,6 @@ int journal_file_verify(
         uint64_t n_weird = 0, n_objects = 0, n_entries = 0, n_data = 0, n_fields = 0, n_data_hash_tables = 0, n_field_hash_tables = 0, n_entry_arrays = 0, n_tags = 0;
         usec_t last_usec = 0;
         int data_fd = -1, entry_fd = -1, entry_array_fd = -1;
-        char data_path[] = "/var/tmp/journal-data-XXXXXX",
-                entry_path[] = "/var/tmp/journal-entry-XXXXXX",
-                entry_array_path[] = "/var/tmp/journal-entry-array-XXXXXX";
         unsigned i;
         bool found_last;
 #ifdef HAVE_GCRYPT
@@ -808,29 +805,26 @@ int journal_file_verify(
         } else if (f->seal)
                 return -ENOKEY;
 
-        data_fd = mkostemp(data_path, O_CLOEXEC);
+        data_fd = open_tmpfile("/var/tmp", O_RDWR | O_CLOEXEC);
         if (data_fd < 0) {
                 log_error("Failed to create data file: %m");
                 r = -errno;
                 goto fail;
         }
-        unlink(data_path);
 
-        entry_fd = mkostemp(entry_path, O_CLOEXEC);
+        entry_fd = open_tmpfile("/var/tmp", O_RDWR | O_CLOEXEC);
         if (entry_fd < 0) {
                 log_error("Failed to create entry file: %m");
                 r = -errno;
                 goto fail;
         }
-        unlink(entry_path);
 
-        entry_array_fd = mkostemp(entry_array_path, O_CLOEXEC);
+        entry_array_fd = open_tmpfile("/var/tmp", O_RDWR | O_CLOEXEC);
         if (entry_array_fd < 0) {
                 log_error("Failed to create entry array file: %m");
                 r = -errno;
                 goto fail;
         }
-        unlink(entry_array_path);
 
 #ifdef HAVE_GCRYPT
         if ((le32toh(f->header->compatible_flags) & ~HEADER_COMPATIBLE_SEALED) != 0)

src/shared/util.c

@@ -6108,3 +6108,25 @@ int getpeersec(int fd, char **ret) {
         *ret = s;
         return 0;
 }
+
+int open_tmpfile(const char *path, int flags) {
+        int fd;
+        char *p;
+
+#ifdef O_TMPFILE
+        fd = open(path, flags|O_TMPFILE, S_IRUSR|S_IWUSR);
+        if (fd >= 0)
+                return fd;
+#endif
+        p = strappenda(path, "/systemd-tmp-XXXXXX");
+
+        RUN_WITH_UMASK(0077) {
+                fd = mkostemp(p, O_RDWR|O_CLOEXEC);
+        }
+
+        if (fd < 0)
+                return -errno;
+
+        unlink(p);
+        return fd;
+}

src/shared/util.h

@@ -849,3 +849,5 @@ bool pid_valid(pid_t pid);
 
 int getpeercred(int fd, struct ucred *ucred);
 int getpeersec(int fd, char **ret);
+
+int open_tmpfile(const char *path, int flags);