Messages in this thread | | | Date | Fri, 10 Aug 2007 19:09:32 +0400 | From | Pavel Emelyanov <> | Subject | Re: [PATCH] Make access to task's nsproxy liter |
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Oleg Nesterov wrote: > On 08/10, Serge E. Hallyn wrote: >> Quoting Pavel Emelyanov (xemul@openvz.org): >>> +/* >>> + * the namespaces access rules are: >>> + * >>> + * 1. only current task is allowed to change tsk->nsproxy pointer or >>> + * any pointer on the nsproxy itself >>> + * >>> + * 2. when accessing (i.e. reading) current task's namespaces - no >>> + * precautions should be taken - just dereference the pointers >>> + * >>> + * 3. the access to other task namespaces is performed like this >>> + * rcu_read_lock(); >>> + * nsproxy = task_nsproxy(tsk); >>> + * if (nsproxy != NULL) { >>> + * / * >>> + * * work with the namespaces here >>> + * * e.g. get the reference on one of them >>> + * * / >>> + * } / * >>> + * * NULL task_nsproxy() means that this task is >>> + * * almost dead (zombie) >>> + * * / >>> + * rcu_read_unlock(); >> And lastly, I guess that the caller to switch_task_namespaces() has >> to ensure that new_nsproxy either (1) is the init namespace, (2) is a >> brand-new namespace to which noone else has a reference, or (3) the >> caller has to hold a reference to the new_nsproxy across the call to >> switch_task_namespaces(). >> >> As it happens the current calls fit (1) or (2). Again if we happen to >> jump into the game of switching a task into another task's nsproxy, >> we'll need to be mindful of (3) so that new_nsproxy can't be tossed into >> the bin between >> >> if (new) >> get_nsproxy(new); > > 4) Unless tsk == current, get_task_namespaces(tsk) and get_nsproxy(tsk) > are racy even if done under rcu_read_lock().
Yup :)
It is already written in comment that only the current is allowed to change its nsproxy. I.e. when switch_task_nsproxy() is called for tsk other than current it's a BUG
> Oleg. > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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