tmpfiles: set mode and owner of d/D directories through an fd

makedir() swallows EEXIST, so the chmod branch for directories that
already existed never ran, while chown() ran every time.  On finix
/var/empty is immutable, which gave a warning on every boot even
though the owner was already correct.

mksubsys() is the original of this code and has the same shape, the
dbus plugin uses it for /tmp/dbus.  Both now go through dirperm(),
which opens the directory and uses fstat/fchmod/fchown on the fd,
changing only what differs.  A failed chown in mksubsys() is a warning
now rather than err(1), PID 1 should not exit over a directory it
cannot adjust.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
(cherry picked from commit 3a72d1263c)

src/tmpfiles.c

@@ -557,11 +557,11 @@ static void tmpfiles(char *line)
 				if (gid < 0)
 					gid = 0;
 
-				rc = makedir(path, mode ?: 0755);
-				if (rc && errno == EEXIST)
-					rc = chmod(path, mode ?: 0755);
-				if (chown(path, uid, gid))
-					warn("Failed chown(%s, %d, %d)", path, uid, gid);
+				if (!mode)
+					mode = 0755;
+				rc = makedir(path, mode);
+				if (!rc && dirperm(path, mode, uid, gid))
+					warn("Failed setting mode/owner on %s", path);
 			}
 			umask(omask);
 			break;

src/util.c

@@ -25,6 +25,7 @@
 
 #include <ctype.h>		/* isprint() */
 #include <errno.h>
+#include <fcntl.h>
 #include <grp.h>
 #include <pwd.h>
 #ifdef HAVE_MNTENT_H
@@ -374,6 +375,32 @@ int rmrf(const char *path)
 	return 0;
 }
 
+/*
+ * Set mode and owner on a directory that may already exist.  Works on
+ * an fd opened with O_NOFOLLOW | O_DIRECTORY, so the change lands on
+ * the directory itself and not on whatever a link at @path points to.
+ * Only what differs is touched, the directory may be immutable.  uid
+ * -1 skips the chown.
+ */
+int dirperm(const char *path, mode_t mode, uid_t uid, gid_t gid)
+{
+	struct stat st;
+	int fd, rc;
+
+	fd = open(path, O_RDONLY | O_DIRECTORY | O_NOFOLLOW | O_CLOEXEC);
+	if (fd < 0)
+		return -1;
+
+	rc = fstat(fd, &st);
+	if (!rc && (st.st_mode & 07777) != mode)
+		rc = fchmod(fd, mode);
+	if (!rc && uid != (uid_t)-1 && (st.st_uid != uid || st.st_gid != gid))
+		rc = fchown(fd, uid, gid);
+	close(fd);
+
+	return rc;
+}
+
 /*
  * Like mksubsys() but with the ids already resolved, uid -1 skips the
  * chown.  Parents are created 0755, only the leaf gets @mode.
@@ -386,11 +413,8 @@ int mksubsysd(const char *dir, mode_t mode, uid_t uid, gid_t gid)
 	omask = umask(0);
 
 	rc = mkpath(dir, 0755);
-	if (!rc) {
-		rc = chmod(dir, mode);
-		if (!rc && uid != (uid_t)-1 && chown(dir, uid, gid))
-			err(1, "Failed chown(%s, %d, %d)", dir, (int)uid, (int)gid);
-	}
+	if (!rc && dirperm(dir, mode, uid, gid))
+		warn("Failed setting mode/owner on %s", dir);
 
 	umask(omask);
 

src/util.h

@@ -71,6 +71,7 @@ int   getgroup     (const char *group);
 int   getcuser     (char *buf, size_t len);
 int   getcgroup    (char *buf, size_t len);
 
+int   dirperm      (const char *path, mode_t mode, uid_t uid, gid_t gid);
 int   mksubsys     (const char *dir, mode_t mode, char *user, char *group);
 int   mksubsysd    (const char *dir, mode_t mode, uid_t uid, gid_t gid);
 int   chownr       (const char *path, uid_t uid, gid_t gid);