glibc: backport fix for regexec buffer read overrun

Problem found by AddressSanitizer[1]:

 Latest `grep` (git commit 1019e6e) compiled with asan may cause a
 heap-buffer-overflow when `-i` is specified.

     ./grep -i '\(\(\)*.\)*\(\)\(\)\1' /bin/chvt

 =================================================================
 ==16206==ERROR: AddressSanitizer: heap-buffer-overflow on address

1. https://debbugs.gnu.org/34140

Ref: https://sourceware.org/bugzilla/show_bug.cgi?id=24114
Signed-off-by: Alin Nastac <alin.nastac@gmail.com>
[commit title and description facelift]
Signed-off-by: Petr Štetiar <ynezz@true.cz>

toolchain/glibc/patches/001-regex-read-overrun.patch

@@ -0,0 +1,26 @@
+commit 583dd860d5b833037175247230a328f0050dbfe9
+Author: Paul Eggert <eggert@cs.ucla.edu>
+Date:   Mon Jan 21 11:08:13 2019 -0800
+
+    regex: fix read overrun [BZ #24114]
+    
+    Problem found by AddressSanitizer, reported by Hongxu Chen in:
+    https://debbugs.gnu.org/34140
+    * posix/regexec.c (proceed_next_node):
+    Do not read past end of input buffer.
+
+--- 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;
+ 		}
+ 	    }