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;
 		}
 	    }
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<div class='path'>path: <a href='/guix/log/?id=d43795cd208161495391104054e36abb94ea0a89'>root</a>/<a href='/guix/log/tests?id=d43795cd208161495391104054e36abb94ea0a89'>tests</a>/<a href='/guix/log/tests/gnu-maintenance.scm?id=d43795cd208161495391104054e36abb94ea0a89'>gnu-maintenance.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/gnu-maintenance.scm?id=d43795cd208161495391104054e36abb94ea0a89&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-09-27 23:38:21 +0200'>2023-09-27</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=72fc91b113564f8006094c0118f06af0f414d21b'>tests: ‘rewrite-url’ test no longer depends on network access.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2023-08-26 11:38:56 -0400'>2023-08-26</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=1dce88777691b7a38ad66ba58b17a9b368c11e07'>gnu-maintenance: Consider Qt source tarballs as "release files".</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2023-08-26 11:38:56 -0400'>2023-08-26</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=6953fb924111c400a064255d8274a2caa68f7436'>gnu-maintenance: Add support to rewrite version in URL path.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2023-01-02 00:06:51 +0100'>2023-01-02</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=d7a9d72bb02a2a3b1a99183655bf878547116032'>tests: Fix gnu-maintenance tests.</a><span class='msg-avail'>...</span></td><td>Hartmut Goebel</td></tr>
<tr><td><span title='2022-11-11 23:17:43 +0100'>2022-11-11</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=c6cb7243fbf4dfb7766874e403ce0f74f05933a3'>gnu-maintenance: 'release-file?' excludes "valgrind-3.20.0.RC1.tar.bz2".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-09-26 23:29:37 +0200'>2022-09-26</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=5c37ad812b94de76ab45bb15a25aaf7895fb0c66'>gnu-maintenance: Test latest-html-release.</a><span class='msg-avail'>...</span></td><td>Maxime Devos</td></tr>
<tr><td><span title='2022-09-17 19:09:45 +0200'>2022-09-17</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=c967d1153cae419e4acbe0dbed8f558d95ced0e3'>gnu-maintenance: Support // URLs in latest-html-release.</a><span class='msg-avail'>...</span></td><td>Maxime Devos</td></tr>
<tr><td><span title='2021-05-28 23:04:44 +0200'>2021-05-28</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=d7c356edb9719f1e236ee926c0288f914076481a'>gnu-maintenance: 'release-file?' accepts 'v' prefix as in "PKG-v1.2.tgz".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-04-05 12:03:09 +0200'>2021-04-05</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=ceeea60bbc1e2be6a86cef208fcd80eb61c92934'>gnu-maintenance: Recognize more source tarball naming schemes.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-03-29 23:33:40 +0200'>2021-03-29</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=1575da60628cf2594cd7b1ab0812ec4c50ac5092'>gnu-maintenance: Recognize "-source" tarball suffix.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-03-20 22:29:14 +0100'>2021-03-20</span></td><td><a href='/guix/commit/tests/gnu-maintenance.scm?id=1710e8cb59e2ef6f1e0eb19235b6a4f1b8158bc4'>gnu-maintenance: Accept underscores as package/version separators.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>