[Bug libc/18096] null deref in wordexp/parse_dollars/parse_arith

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

https://sourceware.org/bugzilla/show_bug.cgi?id=18096

--- Comment #1 from Kostya Serebryany <konstantin.s.serebryany at gmail dot com> ---
Another similar looking, but on different line: 

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


    #0 0x7fc1c04a26f6 in parse_arith
/build/buildd/eglibc-2.19/posix/wordexp.c:736
    #1 0x7fc1c04a0123 in parse_dollars
/build/buildd/eglibc-2.19/posix/wordexp.c:2096
    #2 0x7fc1c04a2feb in wordexp /build/buildd/eglibc-2.19/posix/wordexp.c:2348


The following stops the bug for me: 
--- a/posix/wordexp.c
+++ b/posix/wordexp.c
@@ -736,7 +736,7 @@ parse_arith (char **word, size_t *word_length, size_t
*max_length,
              ++(*offset);

              /* Go - evaluate. */
-             if (*expr && eval_expr (expr, &numresult) != 0)
+             if (expr && *expr && eval_expr (expr, &numresult) != 0)
                { 
                  free (expr);
                  return WRDE_SYNTAX;
@@ -774,7 +774,7 @@ parse_arith (char **word, size_t *word_length, size_t
*max_length,
              long int numresult = 0;

              /* Go - evaluate. */
-             if (*expr && eval_expr (expr, &numresult) != 0)
+             if (expr && *expr && eval_expr (expr, &numresult) != 0)
                { 
                  free (expr);
                  return WRDE_SYNTAX;

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