On Mon, Feb 15, 2016 at 03:35:19PM +0100, Andrzej Hajda wrote:
> IS_ERR_VALUE should be used only with unsigned long type.
> Otherwise it can work incorrectly. To achieve this function
> xt_percpu_counter_alloc is modified to return unsigned long,
> and its result is assigned to temporary variable to perform
> error checking, before assigning to .pcnt field.
Wrong fix, IMO. Just have an anon union of u64 pcnt and
struct xt_counters __percpu *pcpu in there. And make this
> +static inline unsigned long xt_percpu_counter_alloc(void)
> {
> if (nr_cpu_ids > 1) {
> void __percpu *res = __alloc_percpu(sizeof(struct xt_counters),
> sizeof(struct xt_counters));
>
> if (res == NULL)
> - return (u64) -ENOMEM;
> + return -ENOMEM;
>
> - return (u64) (__force unsigned long) res;
> + return (__force unsigned long) res;
> }
>
> return 0;
take struct xt_counters * and return 0 or -ENOMEM. Storing the result of
allocation in ->pcpu of passed structure.
I mean, look at the callers -
> - e->counters.pcnt = xt_percpu_counter_alloc();
> - if (IS_ERR_VALUE(e->counters.pcnt))
> + pcnt = xt_percpu_counter_alloc();
> + if (IS_ERR_VALUE(pcnt))
> return -ENOMEM;
> + e->counters.pcnt = pcnt;
should be
if (xt_percpu_counter_alloc(&e->counters) < 0)
return -ENOMEM;
and similar for the rest of callers. Moreover, if you look at the _users_
of that fields, you'll see that a bunch of those actually want to use
->pcpu instead of doing all those casts.
Really, that's the point - IS_ERR_VALUE is a big red flag saying "we need
to figure out what's going on in that place", which does include reading
through the code. Mechanical "solutions" like that only hide the problem.
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