Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t

From: Alexey Dobriyan
Date: Mon Jul 10 2017 - 05:35:09 EST

On Mon, Jul 10, 2017 at 11:37 AM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> "Reshetova, Elena" <elena.reshetova@xxxxxxxxx> writes:
> 2>> Elena Reshetova <elena.reshetova@xxxxxxxxx> writes:
>>> > refcount_t type and corresponding API should be
>>> > used instead of atomic_t when the variable is used as
>>> > a reference counter. This allows to avoid accidental
>>> > refcounter overflows that might lead to use-after-free
>>> > situations.
>>> In this patch you can see all of the uses of the count.
>>> What accidental refcount overflows are possible?
>> Even if one can guarantee and prove that in the current implementation
>> there are no overflows possible, we can't say that for
>> sure for any future implementation. Bugs might always happen
>> unfortunately, but if we convert the refcounter to a safer
>> type we can be sure that overflows are not possible.
>> Does it make sense to you?
> Not for code that is likely to remain unchanged for a decade no.
> This looks like a large set of unautomated changes without any real
> thought put into it. That almost always results in a typo somewhere
> that breaks things.

This is nonsense. The wrong code would simply emit a warning
which are caught very quickly.

> So there is no benefit to the code, and a non-zero chance that there
> will be a typo breaking the code.