Messages in this thread | | | Date | Wed, 17 Feb 2016 02:31:27 +0000 | From | Al Viro <> | Subject | Re: [PATCH 1/7] netfilter: fix IS_ERR_VALUE usage |
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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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