On Thu, Feb 10, 2022 at 07:18:24AM -0800, Suren Baghdasaryan wrote:
> On Thu, Feb 10, 2022 at 4:40 AM 'Michal Hocko' via kernel-team
> <kernel-team@xxxxxxxxxxx> wrote:
> >
> > On Wed 09-02-22 20:32:15, Suren Baghdasaryan wrote:
> > > When adjacent vmas are being merged it can result in the vma that was
> > > originally passed to madvise_update_vma being destroyed. In the current
> > > implementation, the name parameter passed to madvise_update_vma points
> > > directly to vma->anon_name->name and it is used after the call to
> > > vma_merge. In the cases when vma_merge merges the original vma and
> > > destroys it, this will result in use-after-free bug as shown below:
> > >
> > > madvise_vma_behavior << passes vma->anon_name->name as name param
> > > madvise_update_vma(name)
> > > vma_merge
> > > __vma_adjust
> > > vm_area_free <-- frees the vma
> > > replace_vma_anon_name(name) <-- UAF
> > >
> > > Fix this by raising the name refcount and stabilizing it. Introduce
> > > vma_anon_name_{get/put} API for this purpose.
> >
> > What is the reason that madvise_update_vma uses the naked name rather
> > than the encapsulated anon_vma_name? This really just begs for problems.
>
> The reason for that is the second place it's being used from the prctl syscall:
>
> prctl_set_vma
> madvise_set_anon_name
> madvise_vma_anon_name
> madvise_update_vma
>
> In that case the name parameter is not part of any anon_vma_name
> struct and therefore is stable. I can add a comment to
> madvise_update_vma indicating that the name parameter has to be stable
> if that helps.
Seems to me it'd simplify things if replace_vma_anon_name() and
madvise_vma_anon_name() took a struct anon_vma_name instead of
a bare char *. You could construct it in madvise_set_anon_name().
