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SubjectRe: [PATCH v6 1/1] ns: add binfmt_misc to the user namespace
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Le 16/10/2018 à 12:13, Rasmus Villemoes a écrit :
> On 2018-10-10 18:14, Laurent Vivier wrote:
>
>> + /* create a new binfmt namespace
>> + * if we are not in the first user namespace
>> + * but the binfmt namespace is the first one
>> + */
>> + if (READ_ONCE(ns->binfmt_ns) == NULL) {
>> + struct binfmt_namespace *new_ns;
>> +
>> + new_ns = kmalloc(sizeof(struct binfmt_namespace),
>> + GFP_KERNEL);
>> + if (new_ns == NULL)
>> + return -ENOMEM;
>> + INIT_LIST_HEAD(&new_ns->entries);
>> + new_ns->enabled = 1;
>> + rwlock_init(&new_ns->entries_lock);
>> + new_ns->bm_mnt = NULL;
>> + new_ns->entry_count = 0;
>> + /* ensure new_ns is completely initialized before sharing it */
>> + smp_wmb();
>> + WRITE_ONCE(ns->binfmt_ns, new_ns);
>> + }
>
> If ns->binfmt_ns can really change under us (given you use READ_ONCE),
> what prevents two instances of this code running at the same time, in
> which case one of them would leak its new_ns instance? Also, there

See
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1782780.html

> doesn't seem to be any smp_rmb() buddy to that wmb(), I don't think
> that's implied by READ_ONCE() in binfmt_ns().

See
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1783049.html

Thanks,
Laurent

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