Re: [PATCH v2 1/1] mm: fix use-after-free when anon vma name is used after vma is freed

[Michal Hocko <mhocko@suse.com>]

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.
-- 
Michal Hocko
SUSE Labs