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;
 		}
 	    }
scripts</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=4c640083f59aa14135c781a9c62a2a144fc42da5'>refs</a><a class='active' href='/guix/log/tests/inferior.scm'>log</a><a href='/guix/tree/tests/inferior.scm?id=4c640083f59aa14135c781a9c62a2a144fc42da5'>tree</a><a href='/guix/commit/tests/inferior.scm?id=4c640083f59aa14135c781a9c62a2a144fc42da5'>commit</a><a href='/guix/diff/tests/inferior.scm?id=4c640083f59aa14135c781a9c62a2a144fc42da5'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/inferior.scm'>
<input type='hidden' name='id' value='4c640083f59aa14135c781a9c62a2a144fc42da5'/><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=4c640083f59aa14135c781a9c62a2a144fc42da5'>root</a>/<a href='/guix/log/tests?id=4c640083f59aa14135c781a9c62a2a144fc42da5'>tests</a>/<a href='/guix/log/tests/inferior.scm?id=4c640083f59aa14135c781a9c62a2a144fc42da5'>inferior.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/inferior.scm?id=4c640083f59aa14135c781a9c62a2a144fc42da5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-21 22:16:02 +0100'>2020-03-21</span></td><td><a href='/guix/commit/tests/inferior.scm?id=d19b14c8349ce8cacb62619ab68953265daeeca7'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-03-19 15:14:08 +0100'>2020-03-19</span></td><td><a href='/guix/commit/tests/inferior.scm?id=1dca6aaafa9f842565deab1fe7e6929f25544551'>inferior: '&amp;inferior-exception' includes a stack trace.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-17 15:46:15 +0100'>2020-03-17</span></td><td><a href='/guix/commit/tests/inferior.scm?id=9d0c2c6e5226bbd11e710bd4efa8f25e9ffb5a86'>tests: Fix up reference to 'guile-2.2'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-12 11:52:38 +0100'>2020-03-12</span></td><td><a href='/guix/commit/tests/inferior.scm?id=f7537e30b892cef09d91902547c00e5fa9b66f3b'>inferior: Distinguish inferior exceptions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-21 16:48:36 +0200'>2019-09-21</span></td><td><a href='/guix/commit/tests/inferior.scm?id=71507435225f10d8d944ba183cbcc77ef953e0e5'>inferior: Propagate '&amp;store-protocol-error' error conditions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-02-12 23:30:16 +0100'>2019-02-12</span></td><td><a href='/guix/commit/tests/inferior.scm?id=739380542da7e434c581ec620edeb4348d6ece89'>inferior: Add 'inferior-available-packages'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>