[NetworkManager-vpnc] service: disallow newlinies in configuration values (CVE-2018-10900)

[Lubomir Rintel <lkundrak src gnome org>]

commit 07ac18a32b4e361a27ef48ac757d36cbb46e8e12
Author: Lubomir Rintel <lkundrak v3 sk>
Date:   Fri Jul 13 18:51:04 2018 +0200

    service: disallow newlinies in configuration values (CVE-2018-10900)
    
    The vpnc configuration format doesn't allow those. vpnc(8):
    
      The values start exactly one space after the keywords, and run to the end
      of line. This lets you put any kind of weird character (except CR, LF and
      NUL) in your strings
    
    We have no choice but to reject them. If we didn't it would allow the
    user to inject arbitrary configuration directives with potential
    security implications.
    
    https://pulsesecurity.co.nz/advisories/NM-VPNC-Privesc
    
    Reported by: Denis Andzakovic

 src/nm-vpnc-service.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/src/nm-vpnc-service.c b/src/nm-vpnc-service.c
index 364ff7c..802f5ac 100644
--- a/src/nm-vpnc-service.c
+++ b/src/nm-vpnc-service.c
@@ -209,7 +209,14 @@ validate_one_property (const char *key, const char *value, gpointer user_data)
                break; /* technically valid, but unused */
        case ITEM_TYPE_STRING:
        case ITEM_TYPE_SECRET:
-               break; /* valid */
+               if (strchr (value, '\n') || strchr (value, '\r')) {
+                       g_set_error (info->error,
+                                    NM_VPN_PLUGIN_ERROR,
+                                    NM_VPN_PLUGIN_ERROR_BAD_ARGUMENTS,
+                                    _("property “%s” contains a newline character"),
+                                    key);
+               }
+               break;
        case ITEM_TYPE_PATH:
                if (   !value
                    || !strlen (value)