Fix buffer overread in libevents DNS code.

Upstream bug report:

https://github.com/libevent/libevent/issues/317

Patch copied from upstream source repository:

https://github.com/libevent/libevent/commit/96f64a022014a208105ead6c8a7066018449d86d

From 3c570970516f48da35f42fef98276531fcc0abaa Mon Sep 17 00:00:00 2001
From: Azat Khuzhin <a3at.mail@gmail.com>
Date: Mon, 1 Feb 2016 17:32:09 +0300
Subject: [PATCH] evdns: name_parse(): fix remote stack overread

---
 evdns.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/evdns.c b/evdns.c
index 60b10485..137c24ea 100644
--- a/evdns.c
+++ b/evdns.c
@@ -960,7 +960,6 @@ name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
 
 	for (;;) {
 		u8 label_len;
-		if (j >= length) return -1;
 		GET8(label_len);
 		if (!label_len) break;
 		if (label_len & 0xc0) {
@@ -981,6 +980,7 @@ name_parse(u8 *packet, int length, int *idx, char *name_out, int name_out_len) {
 			*cp++ = '.';
 		}
 		if (cp + label_len >= end) return -1;
+		if (j + label_len > length) return -1;
 		memcpy(cp, packet + j, label_len);
 		cp += label_len;
 		j += label_len;
-- 
2.11.0

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<div class='path'>path: <a href='/guix/log/?id=ffca429baa30ad0fb9db3e2db956cc8a8dbf4887'>root</a>/<a href='/guix/log/tests?id=ffca429baa30ad0fb9db3e2db956cc8a8dbf4887'>tests</a>/<a href='/guix/log/tests/builders.scm?id=ffca429baa30ad0fb9db3e2db956cc8a8dbf4887'>builders.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/tests/builders.scm?id=ffca429baa30ad0fb9db3e2db956cc8a8dbf4887&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-26 17:36:58 +0200'>2023-09-26</span></td><td><a href='/guix/commit/tests/builders.scm?id=13b0cf85eb31e1b1ea674debbbfb0f35a32d1374'>git-download: Use “builtin:git-download” when available.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;https://issues.guix.gnu.org/63331&gt;.

Longer-term this will remove Git from the derivation graph when its sole
use is to perform a checkout for a fixed-output derivation, thereby
breaking dependency cycles that can arise in these situations.

* guix/git-download.scm (git-fetch): Rename to…
(git-fetch/in-band): … this.  Deal with GIT or GUILE being #f.
(git-fetch/built-in, built-in-builders*, git-fetch): New procedures.
* tests/builders.scm ("git-fetch, file URI"): New test.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-10-22 01:46:55 +0200'>2022-10-22</span></td><td><a href='/guix/commit/tests/builders.scm?id=a3619079f95213c4f983e69210ed12b38fd31022'>Remove now unnecessary uses of (guix grafts).</a><span class='msg-avail'>...<span class='msg-tooltip'>These modules would use (guix grafts) just to access '%graft?' and
related bindings, which are now in (guix store).

* gnu/ci.scm,
guix/gexp.scm,
guix/lint.scm,
guix/scripts.scm,
guix/scripts/archive.scm,
guix/scripts/build.scm,
guix/scripts/challenge.scm,
guix/scripts/deploy.scm,
guix/scripts/environment.scm,
guix/scripts/home.scm,
guix/scripts/pack.scm,
guix/scripts/package.scm,
guix/scripts/pull.scm,
guix/scripts/size.scm,
guix/scripts/system.scm,
guix/scripts/weather.scm,
tests/builders.scm,
tests/channels.scm,
tests/cpan.scm,
tests/derivations.scm,
tests/gexp.scm,
tests/graph.scm,
tests/guix-daemon.sh,
tests/monads.scm,
tests/pack.scm,
tests/packages.scm,
tests/profiles.scm,
tests/system.scm: Remove #:use-module (guix grafts).
</span></span></td><td>Ludovic Courtès</td></tr>