[Bug libc/18043] New: buffer-overflow (read past the end) in wordexp/parse_dollars/parse_param

["konstantin.s.serebryany at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18043

            Bug ID: 18043
           Summary: buffer-overflow (read past the end) in
                    wordexp/parse_dollars/parse_param
           Product: glibc
           Version: 2.21
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: konstantin.s.serebryany at gmail dot com
                CC: drepper.fsp at gmail dot com
             Flags: security+

#include <wordexp.h>
#include <string.h>
int main() {
  char *p = strdup("${");
  wordexp_t w;
  wordexp(p, &w, 0);
}

==15405== Invalid read of size 1
==15405==    at 0x4F1DE5C: parse_param (wordexp.c:1428)
==15405==    by 0x4F1DE5C: parse_dollars (wordexp.c:2102)
==15405==    by 0x4F1FFEB: wordexp (wordexp.c:2348)
==15405==    by 0x4005AA: main
==15405==  Address 0x51fb043 is 0 bytes after a block of size 3 alloc'd
==15405==    at 0x4C2ABBD: malloc (vg_replace_malloc.c:296)
==15405==    by 0x4EBE839: strdup (strdup.c:42)
==15405==    by 0x40058E: main

This time it's unclear to me how bad this bug is because 
the man page explicitly says that 
"there must not be any unescaped newline or |, &, ;, <, >, (, ), {, }
characters"
OTOH, buffer overflow is still a bit too much. 

2.19 and fresh trunk are affected.
Same fuzzer, see https://sourceware.org/glibc/wiki/FuzzingLibc

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