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;
3241cccb80ff9056ed0c087a3bef4b0327'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/avahi.scm'>
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<div class='path'>path: <a href='/guix/log/?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327'>root</a>/<a href='/guix/log/gnu?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327'>gnu</a>/<a href='/guix/log/gnu/services?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327'>services</a>/<a href='/guix/log/gnu/services/avahi.scm?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327'>avahi.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/services/avahi.scm?id=b7210a3241cccb80ff9056ed0c087a3bef4b0327&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-01-19 06:09:01 +0100'>2020-01-19</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=f460f8da68f915dee5aa3ce97e05ba38c92f3106'>gnu: Use HTTPS for avahi.org everywhere.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/avahi.scm (avahi)[home-page]: Use HTTPS.
* gnu/services/avahi.scm (avahi-service): Likewise in docstring.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-01-16 14:07:37 +0100'>2019-01-16</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=2e04ab7147948b51d4e437ca9ba910530ac2a788'>services: avahi: Deprecate the 'avahi-service' procedure.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/avahi.scm (&lt;avahi-configuration&gt;): Export getters.  Add
default values.
(avahi-service-type)[default-value]: New field.
(avahi-service): Mark as deprecated.
* gnu/services/desktop.scm (%desktop-services): Use the 'service' form
instead of calling 'avahi-service'.
* gnu/tests/base.scm (%avahi-os): Likewise.
* doc/guix.texi (Base Services): Adjust example accordingly.
(Networking Services): Update accordingly.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-02-19 00:33:34 +0100'>2018-02-19</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=37084ba5613d3ef9d38c7e8d0ea6ac3d4155cea9'>services: avahi: Publish '_workstation._tcp' by default.</a><span class='msg-avail'>...<span class='msg-tooltip'>This reverts to the behavior of avahi-daemon prior to Avahi 0.7 (commit
550f4509acf2c0f67882260414b0bb2843e07465).

* gnu/services/avahi.scm (&lt;avahi-configuration&gt;)[publish-workstation?]:
New field.
(configuration-file): Honor it.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-02-19 00:33:34 +0100'>2018-02-19</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=ad7a807d84827f504d492cc1e2ac84f287fd29f6'>services: avahi: Read PID file from /run.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/avahi.scm (%avahi-activation, avahi-shepherd-service):
Use /run/avahi-daemon/ instead of /var/run/avahi-daemon/.  This was the
case since the switch to Avahi 0.7 (commit
550f4509acf2c0f67882260414b0bb2843e07465).
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-02-15 10:16:00 +0100'>2018-02-15</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=9859b5c190b43a2d53f03f1ac71bad20c74b632b'>gnu: nss-mdns: Update to 0.12.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/avahi.scm (nss-mdns): Update to 0.12 + patch.
(nss-mdns-0.10.0): Remove.
* gnu/services/avahi.scm (avahi-service-type): Use NSS-MDNS again.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-02-09 15:17:41 +0100'>2018-02-09</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=a68fdfea96370c8a4b95af1fcd6e2fd7eb72da29'>services: avahi: Default to nss-mdns 0.10.</a><span class='msg-avail'>...<span class='msg-tooltip'>This works around &lt;https://bugs.gnu.org/30396&gt;.
Reported by George myglc2 Clemmer &lt;myglc2@gmail.com&gt;.

* gnu/packages/avahi.scm (nss-mdns-0.10): New variable.
* gnu/services/avahi.scm (avahi-service-type): Use it.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2017-11-05 15:29:52 +0100'>2017-11-05</span></td><td><a href='/guix/commit/gnu/services/avahi.scm?id=21b71b01e9c2264c31ef30451c152bb38cc9e635'>services: Add 'description' fields.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/admin.scm (rottlog-service-type)
(tailon-service-type): Add 'description' field.
* gnu/services/audio.scm (mpd-service-type): Likewise.
* gnu/services/avahi.scm (avahi-service-type): Likewise.
* gnu/services/ssh.scm (lsh-service-type)
(openssh-service-type, dropbear-service-type): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>