Fix <https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-9169>.

Taken from this upstream commit, sans ChangeLog updates:
https://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commitdiff;h=583dd860d5b833037175247230a328f0050dbfe9

diff --git a/posix/regexec.c b/posix/regexec.c
index 91d5a797b8..084b1222d9 100644
--- a/posix/regexec.c
+++ b/posix/regexec.c
@@ -1293,8 +1293,10 @@ proceed_next_node (const re_match_context_t *mctx, Idx nregs, regmatch_t *regs,
 	      else if (naccepted)
 		{
 		  char *buf = (char *) re_string_get_buffer (&mctx->input);
-		  if (memcmp (buf + regs[subexp_idx].rm_so, buf + *pidx,
-			      naccepted) != 0)
+		  if (mctx->input.valid_len - *pidx < naccepted
+		      || (memcmp (buf + regs[subexp_idx].rm_so, buf + *pidx,
+				  naccepted)
+			  != 0))
 		    return -1;
 		}
 	    }
s</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>refs</a><a class='active' href='/guix/log/CODE-OF-CONDUCT'>log</a><a href='/guix/tree/CODE-OF-CONDUCT?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>tree</a><a href='/guix/commit/CODE-OF-CONDUCT?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>commit</a><a href='/guix/diff/CODE-OF-CONDUCT?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/CODE-OF-CONDUCT'>
<input type='hidden' name='id' value='6b5b09f1d2d0e825bb2a31103460c12efccce8a4'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>root</a>/<a href='/guix/log/CODE-OF-CONDUCT?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4'>CODE-OF-CONDUCT</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/CODE-OF-CONDUCT?id=6b5b09f1d2d0e825bb2a31103460c12efccce8a4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-05-29 18:29:36 +0200'>2018-05-29</span></td><td><a href='/guix/commit/CODE-OF-CONDUCT?id=a076f19908d06b6df49f1c25c40de8838213cd71'>CODE-OF-CONDUCT: Switch to version 1.4 of the Contributor Covenant.</a><span class='msg-avail'>...<span class='msg-tooltip'>See the discussion at
&lt;https://lists.gnu.org/archive/html/guix-devel/2018-05/msg00146.html&gt;.

* CODE-OF-CONDUCT: Adapt from version 1.4 of the Contributor Covenant.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-04-04 23:45:57 +0200'>2016-04-04</span></td><td><a href='/guix/commit/CODE-OF-CONDUCT?id=e314ce1bd7b21229c750ab7132feac8189da87ba'>CoC: Clarify which project we're talking about.</a><span class='msg-avail'>...<span class='msg-tooltip'>* CODE-OF-CONDUCT: Define "project" and "project maintainer" as
suggested by rms.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-12-09 14:29:41 +0100'>2015-12-09</span></td><td><a href='/guix/commit/CODE-OF-CONDUCT?id=e15fcdd149cec662fcaf4b550ee32879bd53a591'>Add "Contributor Covenant".</a><span class='msg-avail'>...<span class='msg-tooltip'>* CODE-OF-CONDUCT: New file, adapted from
  &lt;http://contributor-covenant.org/version/1/3/0/code_of_conduct.txt&gt;.
* doc/contributing.texi (Contributing): Mention it.
* Makefile.am (EXTRA_DIST): Add it.
</span></span></td><td>Ludovic Courtès</td></tr>