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;
 		}
 	    }
o-scripts'>koszko-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=44d6092022d9f2227eafbc734c2ce23b91585124'>refs</a><a class='active' href='/guix/log/gnu/system/linux-initrd.scm'>log</a><a href='/guix/tree/gnu/system/linux-initrd.scm?id=44d6092022d9f2227eafbc734c2ce23b91585124'>tree</a><a href='/guix/commit/gnu/system/linux-initrd.scm?id=44d6092022d9f2227eafbc734c2ce23b91585124'>commit</a><a href='/guix/diff/gnu/system/linux-initrd.scm?id=44d6092022d9f2227eafbc734c2ce23b91585124'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/system/linux-initrd.scm'>
<input type='hidden' name='id' value='44d6092022d9f2227eafbc734c2ce23b91585124'/><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=44d6092022d9f2227eafbc734c2ce23b91585124'>root</a>/<a href='/guix/log/gnu?id=44d6092022d9f2227eafbc734c2ce23b91585124'>gnu</a>/<a href='/guix/log/gnu/system?id=44d6092022d9f2227eafbc734c2ce23b91585124'>system</a>/<a href='/guix/log/gnu/system/linux-initrd.scm?id=44d6092022d9f2227eafbc734c2ce23b91585124'>linux-initrd.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/gnu/system/linux-initrd.scm?id=44d6092022d9f2227eafbc734c2ce23b91585124&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-15 17:32:10 +0100'>2020-12-15</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=6a060ff27ff68384d7c90076baa36c349fff689d'>store-copy: 'populate-store' can optionally deduplicate files.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-12-06 16:11:43 +0100'>2020-12-06</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=10defc57bf342d9f093c6a84ec1c3c818057c27d'>linux-initrd: Add bcachefs support.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-11-26 00:05:39 +0100'>2020-11-26</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=a9a2fdaabcc78e7a54d9a6bcfa4ee3de308e9a90'>mapped-devices: Add 'lvm-device-mapping'.</a><span class='msg-avail'>...</span></td><td>Mikhail Tsykalov</td></tr>
<tr><td><span title='2020-11-26 00:05:39 +0100'>2020-11-26</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=788df2ecd62d5c2fc0d94928f45c947e6393e20b'>mapped-devices: Allow target to be list of strings.</a><span class='msg-avail'>...</span></td><td>Mikhail Tsykalov</td></tr>
<tr><td><span title='2020-08-25 11:53:20 +0200'>2020-08-25</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=755f365b02b42a5d1e8ef3000dadef069553a478'>linux-libre: Support module compression.</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-05-16 00:34:41 +0200'>2020-05-16</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=12adffd43efe381e9d634d01242ba1988c65ce5c'>linux-initrd: Silence Guile warnings.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-05-05 20:43:21 +0200'>2020-05-05</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=87a40d7203a813921b3ef0805c2b46c0026d6c31'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-05-03 23:04:59 +0200'>2020-05-03</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=33eab4a10dcd2a6580f168f18455df1d4653d14b'>linux-initrd: Provide fsck for F2FS.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2020-05-02 17:31:28 +0200'>2020-05-02</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=50e6c1bf2ef2f006baa8cac80dfbb12ca2ba6d64'>Merge branch 'master' into core-updates</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-05-02 10:54:39 +0200'>2020-05-02</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=27efeef3068bfa21011ea509e21efcbe8c353b5f'>linux-initrd: Add initial support for F2FS.</a><span class='msg-avail'>...</span></td><td>raingloom</td></tr>
<tr><td><span title='2020-05-01 22:06:34 +0200'>2020-05-01</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=57833803b446484b6f413fb883b2156933c38639'>gnu: linux-initrd: Use Guile 3.0.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-01-03 13:54:13 +0100'>2020-01-03</span></td><td><a href='/guix/commit/gnu/system/linux-initrd.scm?id=c7b5cfb014243528f481e8bb95b7a58de17d0772'>linux-initrd: Add support for JFS.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>