[PATCH] ensure NULL deref can't possibly happen in is_exported()

If CONFIG_KALLSYMS is defined and if it should happen that is_exported() is
given a NULL 'mod' and lookup_symbol(name, __start___ksymtab,
__stop___ksymtab) returns 0, then we'll end up dereferencing a NULL
pointer.
Signed-off-by: NJesper Juhl <jesper.juhl@gmail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

kernel/module.c

@@ -1326,7 +1326,7 @@ int is_exported(const char *name, const struct module *mod)
 	if (!mod && lookup_symbol(name, __start___ksymtab, __stop___ksymtab))
 		return 1;
 	else
-		if (lookup_symbol(name, mod->syms, mod->syms + mod->num_syms))
+		if (mod && lookup_symbol(name, mod->syms, mod->syms + mod->num_syms))
 			return 1;
 		else
 			return 0;