Fix CVE-2020-10595:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10595

Patch copied from upstream advisory:

https://seclists.org/oss-sec/2020/q1/128

diff --git a/prompting.c b/prompting.c
index e985d95..d81054f 100644
--- a/prompting.c
+++ b/prompting.c
@@ -314,26 +314,27 @@ pamk5_prompter_krb5(krb5_context context UNUSED, void *data, const char *name,
     /*
      * Reuse pam_prompts as a starting index and copy the data into the reply
      * area of the krb5_prompt structs.
      */
     pam_prompts = 0;
     if (name != NULL && !args->silent)
         pam_prompts++;
     if (banner != NULL && !args->silent)
         pam_prompts++;
     for (i = 0; i < num_prompts; i++, pam_prompts++) {
-        size_t len;
+        size_t len, allowed;

         if (resp[pam_prompts].resp == NULL)
             goto cleanup;
         len = strlen(resp[pam_prompts].resp);
-        if (len > prompts[i].reply->length)
+        allowed = prompts[i].reply->length;
+        if (allowed == 0 || len > allowed - 1)
             goto cleanup;

         /*
          * The trailing nul is not included in length, but other applications
          * expect it to be there.  Therefore, we copy one more byte than the
          * actual length of the password, but set length to just the length of
          * the password.
          */
         memcpy(prompts[i].reply->data, resp[pam_prompts].resp, len + 1);
         prompts[i].reply->length = (unsigned int) len;
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<div class='path'>path: <a href='/guix/log/?id=dd94c3d34008a29a1e05bdc43bb81ef9378f2613'>root</a>/<a href='/guix/log/gnu?id=dd94c3d34008a29a1e05bdc43bb81ef9378f2613'>gnu</a>/<a href='/guix/log/gnu/tests?id=dd94c3d34008a29a1e05bdc43bb81ef9378f2613'>tests</a>/<a href='/guix/log/gnu/tests/ldap.scm?id=dd94c3d34008a29a1e05bdc43bb81ef9378f2613'>ldap.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/tests/ldap.scm?id=dd94c3d34008a29a1e05bdc43bb81ef9378f2613&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-03-20 20:31:15 +0100'>2019-03-20</span></td><td><a href='/guix/commit/gnu/tests/ldap.scm?id=c16423f143919916a5273761d7ed29bd49f14519'>services: Add nslcd-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/authentication.scm (nslcd-service-type, nslcd-configuration,
%nslcd-accounts): New variables.
(uglify-field-name, value-&gt;string, serialize-field, serialize-list,
ssl-option?, tls-reqcert-option?, deref-option?,
comma-separated-list-of-strings?, serialize-ignore-users-option, log-option?,
serialize-log-option, valid-map?, scope-option?, serialize-scope-option,
map-entry?, list-of-map-entries?, filter-entry?, list-of-filter-entries?,
serialize-filter-entry, serialize-list-of-filter-entries, serialize-map-entry,
serialize-list-of-map-entries, nslcd-config-file, nslcd-etc-service,
nslcd-shepherd-service, pam-ldap-pam-services, pam-ldap-pam-service,
generate-nslcd-documentation): New procedures.
* gnu/tests/ldap.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.
* doc/guix.texi (LDAP Services): Document it.
</span></span></td><td>Ricardo Wurmus</td></tr>