Re: [PATCH 12/13] tracing/uprobes: Add more fetch functions

[Namhyung Kim]

On Mon, 4 Nov 2013 17:44:31 +0100, Oleg Nesterov wrote:
> On 11/04, Namhyung Kim wrote:
>>
>> On Thu, 31 Oct 2013 19:22:18 +0100, Oleg Nesterov wrote:
>> > On 10/29, Namhyung Kim wrote:
>> >>
>> >> +static void __user *get_user_vaddr(unsigned long addr, struct trace_uprobe *tu)
>> >> +{
>> >> +	unsigned long pgoff = addr >> PAGE_SHIFT;
>> >> +	struct vm_area_struct *vma;
>> >> +	struct address_space *mapping;
>> >> +	unsigned long vaddr = 0;
>> >> +
>> >> +	if (tu == NULL) {
>> >> +		/* A NULL tu means that we already got the vaddr */
>> >> +		return (void __force __user *) addr;
>> >> +	}
>> >> +
>> >> +	mapping = tu->inode->i_mapping;
>> >> +
>> >> +	mutex_lock(&mapping->i_mmap_mutex);
>> >> +	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
>> >> +		if (vma->vm_mm != current->mm)
>> >> +			continue;
>> >> +		if (!(vma->vm_flags & VM_READ))
>> >> +			continue;
>> >> +
>> >> +		vaddr = offset_to_vaddr(vma, addr);
>> >> +		break;
>> >> +	}
>> >> +	mutex_unlock(&mapping->i_mmap_mutex);
>> >> +
>> >> +	WARN_ON_ONCE(vaddr == 0);
>> >
>> > Hmm. But unless I missed something this "addr" passed as an argument can
>> > be wrong? And if nothing else this or another thread can unmap the vma?
>>
>> You mean WARN_ON_ONCE here is superfluous?  I admit that it should
>> protect concurrent vma [un]mappings.  Please see my reply in other
>> thread for a new approach.
>
> Whatever we do this address can be unmapped. For example, just because of
> @invalid_address passed to trace_uprobe.c.
>
> We do not really care, copy_from_user() should fail. But we should not
> WARN() in this case.

Okay, I see.  Will remove it in the next spin.

Thanks,
Namhyung
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