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SubjectRe: [PATCH] Fix race in process_vm_rw_core
On Fri, 13 Jan 2012 22:00:28 +1030
Christopher Yeoh <cyeoh@au1.ibm.com> wrote:

> Hi Linus,
>
> Below is a patch which fixes the race in process_vm_core found by
> Oleg (http://article.gmane.org/gmane.linux.kernel/1235667/).
> It consolidates some code with mm_for_maps since what they do is almost
> identical.
>
> Oleg - I've kept the breakout of ptrace_may_attach and get_task_mm to
> preserve only having to take the task lock once. I see some performance
> difference with a microbenchmark but haven't had a chance to test with
> some HPC benchmarks yet so for the moment I'd like to leave it in. At
> this stage I think its more important to get the race fixed and I'm at
> Linux.conf.au all next week. I'll send a patch out for the
> rw_copy_check_uvector cleanup after I get back from LCA.
>
> ...
>
> +struct mm_struct *get_check_task_mm(struct task_struct *task, unsigned int mode)
> +{
> + struct mm_struct *mm;
> + int err;
> +
> + err = mutex_lock_killable(&task->signal->cred_guard_mutex);
> + if (err)
> + return ERR_PTR(err);
> +
> + task_lock(task);
> + if (__ptrace_may_access(task, mode)) {
> + mm = ERR_PTR(-EACCES);
> + goto out;
> + }
> +
> + mm = task->mm;
> + if (mm) {
> + if (task->flags & PF_KTHREAD)
> + mm = NULL;
> + else
> + atomic_inc(&mm->mm_users);
> + }
> +
> +out:
> + task_unlock(task);
> + mutex_unlock(&task->signal->cred_guard_mutex);
> +
> + return mm;
> +}
> +EXPORT_SYMBOL_GPL(get_check_task_mm);

I don't think the export is needed - CONFIG_PROC_FS=m isn't supported.

btw, I'm trying to work out why we didn't make the whole process_vm_access.o
feature Kconfigurable, so people who don't want it do not get burdened
with it?



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