pam_motd: Support multiple motd paths specified, with filename overrides (#69)

Adds specifying multiple paths to motd files and motd.d
directories to be displayed. A colon-separated list of
paths is specified as arguments motd and motd_dir to the
pam_motd module.

This gives packages several options to install motd files to.
By default, the paths are, with highest priority first:
/etc/motd
/run/motd
/usr/lib/motd
/etc/motd.d/
/run/motd.d/
/usr/lib/motd.d/

Which is equivalent to the following arguments:
motd=/etc/motd:/run/motd:/usr/lib/motd
motd_dir=/etc/motd.d:/run/motd.d:/usr/lib/motd.d

Files with the same filename in a lower-priority directory,
as specified by the order in the colon-separated list, are
overridden, meaning PAM will not display them.

This allows a package to contain motd files under
/usr/lib instead of the host configuration in /etc.
A service may also write a dynamically generated motd in
/run/motd.d/ and have PAM display it without needing a
symlink from /etc/motd.d/ installed.

Closes #68

* modules/pam_motd/pam_motd.8.xml: update documentation
* modules/pam_motd/pam_motd.c: add specifying multiple motd paths
* xtests/.gitignore: add generated test script
* xtests/Makefile.am: add test source, scripts and config files
* xtests/tst-pam_motd.c: create
* xtests/tst-pam_motd.sh: create
* xtests/tst-pam_motd1.pamd: create
* xtests/tst-pam_motd1.sh: create
* xtests/tst-pam_motd2.pamd: create
* xtests/tst-pam_motd2.sh: create
* xtests/tst-pam_motd3.pamd: create
* xtests/tst-pam_motd3.sh: create

1 files changed, 69 insertions, 0 deletions

diff --git a/xtests/tst-pam_motd.c b/xtests/tst-pam_motd.c
new file mode 100644
index 00000000..bba2f9d5
--- /dev/null
+++ b/xtests/tst-pam_motd.c
@@ -0,0 +1,69 @@
+/*
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, and the entire permission notice in its entirety,
+ *    including the disclaimer of warranties.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior
+ *    written permission.
+ *
+ * ALTERNATIVELY, this product may be distributed under the terms of
+ * the GNU Public License, in which case the provisions of the GPL are
+ * required INSTEAD OF the above restrictions.  (This clause is
+ * necessary due to a potential bad interaction between the GPL and
+ * the restrictions contained in a BSD-style copyright.)
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+ * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <security/pam_appl.h>
+#include <security/pam_misc.h>
+
+static struct pam_conv conv = {
+    misc_conv,
+    NULL
+};
+
+int main(int argc, char *argv[])
+{
+    pam_handle_t *pamh=NULL;
+    char *tst_arg = NULL;
+    int retval;
+
+    if (argc > 1)
+	tst_arg = argv[1];
+
+    retval = pam_start(tst_arg, NULL, &conv, &pamh);
+
+    retval = pam_open_session(pamh, 0);
+
+    retval = pam_close_session(pamh, 0);
+
+    if (pam_end(pamh,retval) != PAM_SUCCESS) {     /* close Linux-PAM */
+	pamh = NULL;
+	exit(1);
+    }
+
+    return ( retval == PAM_SUCCESS ? 0:1 );       /* indicate success */
+}