Fix CVE-2017-17969:

https://sourceforge.net/p/p7zip/bugs/204/
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-17969

Patch copied from Debian.

Subject: Heap-based buffer overflow in 7zip/Compress/ShrinkDecoder.cpp
Origin: vendor, https://sourceforge.net/p/p7zip/bugs/_discuss/thread/0920f369/27d7/attachment/CVE-2017-17969.patch
Forwarded: https://sourceforge.net/p/p7zip/bugs/_discuss/thread/0920f369/#27d7
Bug: https://sourceforge.net/p/p7zip/bugs/204/
Bug-Debian: https://bugs.debian.org/888297
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2017-17969
Author: Antoine Beaupré <anarcat@debian.org>
Reviewed-by: Salvatore Bonaccorso <carnil@debian.org>
Last-Update: 2018-02-01
Applied-Upstream: 18.00-beta

--- a/CPP/7zip/Compress/ShrinkDecoder.cpp
+++ b/CPP/7zip/Compress/ShrinkDecoder.cpp
@@ -121,8 +121,13 @@ HRESULT CDecoder::CodeReal(ISequentialIn
     {
       _stack[i++] = _suffixes[cur];
       cur = _parents[cur];
+      if (cur >= kNumItems || i >= kNumItems)
+        break;
     }
-    
+
+    if (cur >= kNumItems || i >= kNumItems)
+      break;
+
     _stack[i++] = (Byte)cur;
     lastChar2 = (Byte)cur;
 
' href='/guix/log/manifest.scm'>log</a><a href='/guix/tree/manifest.scm?id=e799307decc7187352fb21c4d78b312c66e9aa78'>tree</a><a href='/guix/commit/manifest.scm?id=e799307decc7187352fb21c4d78b312c66e9aa78'>commit</a><a href='/guix/diff/manifest.scm?id=e799307decc7187352fb21c4d78b312c66e9aa78'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/manifest.scm'>
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<div class='path'>path: <a href='/guix/log/?id=e799307decc7187352fb21c4d78b312c66e9aa78'>root</a>/<a href='/guix/log/manifest.scm?id=e799307decc7187352fb21c4d78b312c66e9aa78'>manifest.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/manifest.scm?id=e799307decc7187352fb21c4d78b312c66e9aa78&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2024-06-24 08:51:43 -0400'>2024-06-24</span></td><td><a href='/guix/commit/manifest.scm?id=7f194852a46edfe47537d11bc39fb1dd20e18b37'>manifest: Streamline; add packages useful for patch review/submission.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2024-04-02 23:28:58 +0200'>2024-04-02</span></td><td><a href='/guix/commit/manifest.scm?id=049273bb8c1ea3d6402db646312acdc4abf4678a'>maint: Add perl to the manifest.</a><span class='msg-avail'>...</span></td><td>Janneke Nieuwenhuizen</td></tr>
<tr><td><span title='2024-01-31 09:07:25 +0100'>2024-01-31</span></td><td><a href='/guix/commit/manifest.scm?id=66dd088d3c3404f5cbe2d4d4c5e8f93d184703b0'>maint: Add gnupg to the manifest.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-09-18 22:12:39 +0200'>2023-09-18</span></td><td><a href='/guix/commit/manifest.scm?id=7bf12820f61179900f9d1f753acf91fd33724976'>maint: Support `guix shell' in Guix's git archive with manifest.scm.</a><span class='msg-avail'>...</span></td><td>Janneke Nieuwenhuizen</td></tr>