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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<tr><td><span title='2022-10-07 15:08:05 -0400'>2022-10-07</span></td><td><a href='/guix/commit/gnu/tests/vnc.scm?id=0169aee33e154c1fa8b299c7f126f3e94a8dc9a4'>tests: xvnc: Do not use specification-&gt;package in OS definition.</a><span class='msg-avail'>...<span class='msg-tooltip'>Doing so would cause the extra package dependencies to not be
correctly registered as dependencies, which would lead to a silent
failure when attempting to load or byte compile the module at the time
guix build itself (e.g., when running 'guix pull').

* gnu/tests/vnc.scm (%xvnc-os) [packages]: Turn the the
specification-&gt;package declaration into a list of package objects.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-10-07 15:07:48 -0400'>2022-10-07</span></td><td><a href='/guix/commit/gnu/tests/vnc.scm?id=00e843050012961e9cc41b003ea9271eab718541'>Revert "Revert "services: Add xvnc-service-type.""</a><span class='msg-avail'>...<span class='msg-tooltip'>This reverts commit 0c4966160054bc50e6ab3a4ac9c9a6a1826ab5a0.  The fix appears
in the subsequent commit, for clarity.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-10-07 12:53:22 -0400'>2022-10-07</span></td><td><a href='/guix/commit/gnu/tests/vnc.scm?id=0c4966160054bc50e6ab3a4ac9c9a6a1826ab5a0'>Revert "services: Add xvnc-service-type."</a><span class='msg-avail'>...<span class='msg-tooltip'>This reverts commit 1c528a95cb92b7808e6603d7956185005583629f.  This broke
'guix pull', for (yet) unknown reasons.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-10-07 10:11:13 -0400'>2022-10-07</span></td><td><a href='/guix/commit/gnu/tests/vnc.scm?id=1c528a95cb92b7808e6603d7956185005583629f'>services: Add xvnc-service-type.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/vnc.scm: New file.
* gnu/tests/vnc.scm: Likewise.
* gnu/local.mk: Register them.
</span></span></td><td>Maxim Cournoyer</td></tr>