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>

src/tmpfiles.c

@@ -586,11 +586,11 @@ 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
@@ -280,6 +281,31 @@ int getcgroup(char *buf, size_t len)
 	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.
+ */
+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 && (st.st_uid != uid || st.st_gid != gid))
+		rc = fchown(fd, uid, gid);
+	close(fd);
+
+	return rc;
+}
+
 int mksubsys(const char *dir, mode_t mode, char *user, char *group)
 {
 	mode_t omask;
@@ -295,10 +321,8 @@ int mksubsys(const char *dir, mode_t mode, char *user, char *group)
 			gid = 0;
 
 		rc = makedir(dir, mode);
-		if (rc && errno == EEXIST)
-			rc = chmod(dir, mode);
-		if (chown(dir, uid, gid))
-			err(1, "Failed chown(%s, %d, %d)", dir, uid, gid);
+		if (!rc && dirperm(dir, mode, uid, gid))
+			warn("Failed setting mode/owner on %s", dir);
 	}
 
 	umask(omask);

src/util.h

@@ -68,6 +68,7 @@ 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   fnread       (char *buf, size_t len, char *fmt, ...) __attribute__ ((format (printf, 3, 4)));