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

Oleg.



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