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SubjectRe: [PATCH] fix SEM_UNDO with namespaces, take 2
Manfred Spraul wrote:
> Hi,
>
> below is the second attempt to fix SEM_UNDO + unshare():
> lookup_undo (in ipc/sem.c) is not namespace-aware, thus all entries in
> sysvsem.undo_list must be from the same namespace.
> The patch enforces that by detaching the current thread from
> sysvsem.undo_list in switch_task_namespaces() if the ipc namespace is
> changed.
>
> The patch boots and passes simple sysvsem+unshare tests.
>
> Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
>
> @@ -211,6 +211,18 @@ void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)
>
> might_sleep();
>
> + if ((p->nsproxy == NULL && new != NULL) ||
> + (p->nsproxy != NULL && new == NULL) ||
> + (p->nsproxy != NULL && new != NULL && p->nsproxy->ipc_ns != new->ipc_ns)) {
> + /* switching the IPC namespace is considered equivalent to sys_exit() wrt.
> + * to outstanding SEM_UNDO undos: After switching to the new IPC namespace,
> + * the semaphore arrays from the old namespace are not accessible anymore.
> + *
> + * Additionally, an implicit sys_unshare(CLONE_SYSVSEM) is performed.
> + */
> + exit_sem(p);
> + }
> +

No, switch_task_namespaces is the wrong place to do this. It is to be
done in copy_ipc_ns. If you need a task for which a new namespace is
being prepared, then pass one into it.

> ns = p->nsproxy;
>
> rcu_assign_pointer(p->nsproxy, new);



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