On 10/20, Tycho Andersen wrote:
>
> Hi Kees, Oleg,
>
> On Tue, Oct 20, 2015 at 10:20:24PM +0200, Oleg Nesterov wrote:
> >
> > No, you can't do copy_to_user() from atomic context. You need to pin this
> > filter, drop the lock/irq, then copy_to_user().
>
> Attached is a patch which addresses this.
Looks good to me, feel free to add my reviewed-by.
a couple of questions, I am just curious...
> +long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> + void __user *data)
> +{
> + struct seccomp_filter *filter;
> + struct sock_fprog_kern *fprog;
> + long ret;
> + unsigned long count = 0;
> +
> + if (!capable(CAP_SYS_ADMIN) ||
> + current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> + return -EACCES;
> + }
> +
> + spin_lock_irq(&task->sighand->siglock);
> + if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + filter = task->seccomp.filter;
> + while (filter) {
> + filter = filter->prev;
> + count++;
> + }
> +
> + if (filter_off >= count) {
> + ret = -ENOENT;
> + goto out;
> + }
> + count -= filter_off;
> +
> + filter = task->seccomp.filter;
> + while (filter && count > 1) {
> + filter = filter->prev;
> + count--;
> + }
> +
> + if (WARN_ON(count != 1)) {
> + /* The filter tree shouldn't shrink while we're using it. */
> + ret = -ENOENT;
Yes. but this looks a bit confusing. If we want this WARN_ON() check
because we are paranoid, then we should do
WARN_ON(count != 1 || filter);
And "while we're using it" look misleading, we rely on ->siglock.
Plus if we could be shrinked the additional check can't help anyway,
we can used the free filter. So I don't really understand this check
and "filter != NULL" in the previous "while (filter && count > 1)".
Nevermind...
The question is:
> + fprog = filter->prog->orig_prog;
> + if (!fprog) {
So is it possible or not? I didn't see the previous changes which
added "bool save" to seccomp_attach_filter() so I simply can't know.
Now,
> + /* This must be a new non-cBPF filter, since we save every
> + * every cBPF filter's orig_prog above when
> + * CONFIG_CHECKPOINT_RESTORE is enabled.
> + */
> + ret = -EMEDIUMTYPE;
If this is possible, then probably we should simply change both
"while (filter)" loops above to skip a filter if orig_prog == NULL
and remove the -EMEDIUMTYPE code ?
Or what? Probably "a new non-cBPF filter" answers my question,
but I do not know what this cBPF/non-cBPF actually means ;)
In short. Who can attach a filter without "save => true" ?
Oleg.
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