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='2020-12-08 11:56:26 +0100'>2020-12-08</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=770fb659a62d8adab9a4ba7b44e2760722703879'>services: cuirass: Add queue-size option.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-10-02 14:58:01 +0200'>2020-10-02</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=d6a8f0a9781a90c3037f25e51d7ff32e50f7a8c1'>services: cuirass: Fix activation.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-09-24 13:51:57 +0200'>2020-09-24</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=a024eedb1c0a537aa236fa27fe7a94ba6aa3d76c'>services: cuirass: Create queries log files at activation.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-09-24 11:28:59 +0200'>2020-09-24</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=80e26d74294d40f311f61d13996f1ed1aa4d8edd'>services: cuirass: Add web SQL queries logging support.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-09-24 10:47:22 +0200'>2020-09-24</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=92e507c963470c6086a59ca8e1dd58ed4403649c'>services: cuirass: Add SQL queries logging support.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-03-08 23:46:11 +0000'>2020-03-08</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=af96c1e0e42978594b27bcf957d75b304f107998'>services: cuirass: Allow passing extra command line options.</a><span class='msg-avail'>...</span></td><td>Christopher Baines</td></tr>
<tr><td><span title='2020-01-06 16:31:54 +0100'>2020-01-06</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=6a7c4636d4dec47eefa03c95da5a1315bd0e0413'>Adjust module autoloads.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-10-23 21:48:51 +0200'>2019-10-23</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=b40f4a5995cff00077aa60881737d0d0f6871982'>services: cuirass: Create /var/log/cuirass during activation.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-23 23:41:19 +0200'>2019-09-23</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=46e552cb0f6b7b11600b7c41146f94dce70eee99'>services: cuirass: Remove unneeded conditional.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-08-29 08:06:54 +0200'>2019-08-29</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=3e7a62e2e40fc575d161e4c06ea2e333ab7df3b3'>services: cuirass: Log web interface to separate file.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-08-26 22:21:10 +0200'>2019-08-26</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=159b5e1f8a758e5754ea36929990f09436f4de47'>services: cuirass: Split into two separate services.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>