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;
f'>commit</a><a href='/guix/diff/tests/guix-shell-export-manifest.sh?id=b6d5a7f5836739dab884b49a64ca354794dd845f'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/guix-shell-export-manifest.sh'>
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<div class='path'>path: <a href='/guix/log/?id=b6d5a7f5836739dab884b49a64ca354794dd845f'>root</a>/<a href='/guix/log/tests?id=b6d5a7f5836739dab884b49a64ca354794dd845f'>tests</a>/<a href='/guix/log/tests/guix-shell-export-manifest.sh?id=b6d5a7f5836739dab884b49a64ca354794dd845f'>guix-shell-export-manifest.sh</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/tests/guix-shell-export-manifest.sh?id=b6d5a7f5836739dab884b49a64ca354794dd845f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-06-16 23:57:40 +0200'>2022-06-16</span></td><td><a href='/guix/commit/tests/guix-shell-export-manifest.sh?id=925a57c5d04553ff6c514867348e7d3c5c22ca66'>shell: Fix '--export-manifest' for cached profiles and when '-p' is used.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://issues.guix.gnu.org/55521&gt;.

* guix/scripts/shell.scm (export-manifest): When computing 'manifest',
honor the 'profile key.
* tests/guix-shell-export-manifest.sh: Add test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-06-01 22:22:19 +0200'>2022-06-01</span></td><td><a href='/guix/commit/tests/guix-shell-export-manifest.sh?id=2acc83daa5a3dd1b4ed3f8c32ecadf1313e6fd18'>shell: '--export-manifest -D x -D y' generates a valid manifest.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/shell.scm (manifest-&gt;code*): Add missing 'list' in
generated 'concatenate-manifests' call.
* tests/guix-shell-export-manifest.sh: Add test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-04-08 18:14:35 +0200'>2022-04-08</span></td><td><a href='/guix/commit/tests/guix-shell-export-manifest.sh?id=20691c70cf2c5a61af7f906b65d57a524ecfc4f3'>tests: 'guix shell --export-manifest' test no longer needs networking.</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/guix-shell-export-manifest.sh: Use '--with-input' rather than
'--with-latest' as the latter would crash in the absence of network
access.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-04-04 22:58:04 +0200'>2022-04-04</span></td><td><a href='/guix/commit/tests/guix-shell-export-manifest.sh?id=c42b7baf13c7633b4512e94da7445299c57b247d'>shell: Add '--export-manifest'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/shell.scm (show-help, %options): Add '--export-manifest'.
(manifest-entry-version-prefix, manifest-&gt;code*)
(export-manifest): New procedures.
(guix-shell): Honor '--export-manifest'.
* tests/guix-shell-export-manifest.sh: New file.
* Makefile.am (SH_TESTS): Add it.
* doc/guix.texi (Invoking guix shell): Document '--export-manifest'.
(Invoking guix environment): Link to it.
(Invoking guix pack): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>