pam_cracklib: Add monotonic character sequence checking.

modules/pam_cracklib/pam_cracklib.c (_pam_parse): Parse the maxsequence option.
(sequence): New function to check for too long monotonic sequence of characters.
(password_check): Call the sequence().
modules/pam_cracklib/pam_cracklib.8.xml: Document the maxsequence check.

2 files changed, 64 insertions, 0 deletions

diff --git a/modules/pam_cracklib/pam_cracklib.8.xml b/modules/pam_cracklib/pam_cracklib.8.xml
index 7c0ae700..9c929bfa 100644
--- a/modules/pam_cracklib/pam_cracklib.8.xml
+++ b/modules/pam_cracklib/pam_cracklib.8.xml
@@ -114,6 +114,14 @@
         </listitem>
       </varlistentry>
       <varlistentry>
+        <term>Too long monotonic character sequence</term>
+        <listitem>
+          <para>
+            Optional check for too long monotonic character sequence.
+          </para>
+        </listitem>
+      </varlistentry>
+      <varlistentry>
         <term>Contains user name</term>
         <listitem>
           <para>
@@ -349,6 +357,21 @@
 
         <varlistentry>
           <term>
+            <option>maxsequence=<replaceable>N</replaceable></option>
+          </term>
+          <listitem>
+            <para>
+              Reject passwords which contain monotonic character sequences
+              longer than N. The default is 0 which means that this check
+              is disabled. Examples of such sequence are '12345' or 'fedcb'.
+              Note that most such passwords will not pass the simplicity
+              check unless the sequence is only a minor part of the password.
+            </para>
+          </listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term>
             <option>maxclassrepeat=<replaceable>N</replaceable></option>
           </term>
           <listitem>
diff --git a/modules/pam_cracklib/pam_cracklib.c b/modules/pam_cracklib/pam_cracklib.c
index 4c3030f5..56913477 100644
--- a/modules/pam_cracklib/pam_cracklib.c
+++ b/modules/pam_cracklib/pam_cracklib.c
@@ -101,6 +101,7 @@ struct cracklib_options {
 	int oth_credit;
         int min_class;
 	int max_repeat;
+	int max_sequence;
         int max_class_repeat;
 	int reject_user;
         int gecos_check;
@@ -174,6 +175,10 @@ _pam_parse (pam_handle_t *pamh, struct cracklib_options *opt,
              opt->max_repeat = strtol(*argv+10,&ep,10);
              if (!ep)
                  opt->max_repeat = 0;
+         } else if (!strncmp(*argv,"maxsequence=",12)) {
+             opt->max_sequence = strtol(*argv+12,&ep,10);
+             if (!ep)
+                 opt->max_sequence = 0;
          } else if (!strncmp(*argv,"maxclassrepeat=",15)) {
              opt->max_class_repeat = strtol(*argv+15,&ep,10);
              if (!ep)
@@ -478,6 +483,39 @@ static int consecutive(struct cracklib_options *opt, const char *new)
     return 0;
 }
 
+static int sequence(struct cracklib_options *opt, const char *new)
+{
+    char c;
+    int i;
+    int sequp = 1;
+    int seqdown = 1;
+
+    if (opt->max_sequence == 0)
+	return 0;
+
+    if (new[0] == '\0')
+        return 0;
+
+    for (i = 1; new[i]; i++) {
+        c = new[i-1];
+	if (new[i] == c+1) {
+	    ++sequp;
+	    if (sequp > opt->max_sequence)
+		return 1;
+	    seqdown = 1;
+	} else if (new[i] == c-1) {
+	    ++seqdown;
+	    if (seqdown > opt->max_sequence)
+		return 1;
+	    sequp = 1;
+	} else {
+	    sequp = 1;
+            seqdown = 1;
+        }
+    }
+    return 0;
+}
+
 static int wordcheck(const char *new, char *word)
 {
     char *f, *b;
@@ -622,6 +660,9 @@ static const char *password_check(pam_handle_t *pamh, struct cracklib_options *o
 	if (!msg && consecutive(opt, new))
 	        msg = _("contains too many same characters consecutively");
 
+	if (!msg && sequence(opt, new))
+	        msg = _("contains too long of a monotonic character sequence");
+
 	if (!msg && (usercheck(opt, newmono, usermono) || gecoscheck(pamh, opt, newmono, user)))
 	        msg = _("contains the user name in some form");