do_coredump(): check return from argv_split()

do_coredump() accesses helper_argv[0] without checking helper_argv !=
NULL.  This can happen if page allocation failed.
Signed-off-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/exec.c

@@ -1770,6 +1770,11 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
 
  	if (ispipe) {
 		helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
+		if (!helper_argv) {
+			printk(KERN_WARNING "%s failed to allocate memory\n",
+			       __func__);
+			goto fail_unlock;
+		}
 		/* Terminate the string before the first option */
 		delimit = strchr(corename, ' ');
 		if (delimit)