Re: [PATCH] check_netdev_priv: warn about using netdev priv data after free_netdev

[Pavel Skripkin <paskripkin@gmail.com>]

Hi, Dan!

On 8/3/21 6:08 PM, Dan Carpenter wrote:
> Thanks Pavel!
> 
> It looks really nice.  I've applied it.  I'll test it tonight and push
> tomorrow.
> 
> I don't see any major issues with the check at all, but I have a few
> comments below.
> 
> On Tue, Aug 03, 2021 at 12:00:22AM +0300, Pavel Skripkin wrote:
>> +static void match_free_netdev(const char *fn, struct expression *expr, void *_arg_no)
>> +{
>> +	struct expression *arg;
>> +	const char *name;
>> +
>> +	arg = get_argument_from_call_expr(expr->args, PTR_INT(_arg_no));
>> +	if (!arg)
>> +		return;
>> +
>> +	name = expr_to_var(arg);
>> +	if (!name)
>> +		return;
>> +
>> +	set_state(my_id, name, NULL, &freed);
>> +}
> 
> There is a new param_key API which would make this function shorter.
> 
> static void free_netdev(struct expression *expr, const char *name, struct symbol *sym, void *data)
> {
> 	set_state(my_id, name, NULL, &freed);
> }
> 
> Then in the register function you'd add a hooks like this:
> 
> 	add_function_param_key_hook("free_netdev", &free_netdev, 0, "$", NULL);
> 	add_function_param_key_hook("free_candev", &free_netdev, 0, "$", NULL);
> 

I guess, I missed that API, sorry :( Next time I will use it instead.

> Of course, you've already written your own code which works so it's
> fine.  But that param_key API is really the most awesome thing.
> 
>> +
>> +static void match_symbol(struct expression *expr)
>> +{
>> +	const char *parent_netdev, *name;
>> +	struct smatch_state *state;
>> +
> 
> This hook is run for every variable so it's tempting to add a shortcut
> here:
> 
> 	if (!has_states(my_id))
> 		return;
> 
>> +	name = expr_to_var(expr);
>> +	if (!name)
>> +		return;
>> +
>> +	parent_netdev = get_parent_netdev_name(expr);
>> +	if (!parent_netdev)
>> +		return;
>> +	
>> +	state = get_state(my_id, parent_netdev, NULL);
>> +	if (state == &freed)
>> +		sm_error("Using %s after free_{netdev,candev}(%s);\n", name, parent_netdev);
>> +}
>> +
>> +void check_uaf_netdev_priv(int id)
>> +{
>> +	if (option_project != PROJ_KERNEL)
>> +		return;
>> +
>> +	my_id = id;
>> +
>> +	add_function_hook("free_netdev", &match_free_netdev, NULL);
> 
> NULL works but INT_PTR(0) is nicer.  ;)
> 
>> +	add_function_hook("free_candev", &match_free_netdev, NULL);
>> +	add_modification_hook(my_id, &ok_to_use);
>> +	add_hook(&match_symbol, SYM_HOOK);
>> +}
> 
> Anyway, I think I will probably add the has_states() check but the
> rest isn't important.


Thank you for applying and your guidelines, I appreciate it :)



With regards,
Pavel Skripkin