On Tue 10-07-18 13:48:58, Andrew Morton wrote: > On Tue, 10 Jul 2018 16:48:20 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > vma_is_anonymous() relies on ->vm_ops being NULL to detect anonymous > > VMA. This is unreliable as ->mmap may not set ->vm_ops. > > > > False-positive vma_is_anonymous() may lead to crashes: > > > > ... > > > > This can be fixed by assigning anonymous VMAs own vm_ops and not relying > > on it being NULL. > > > > If ->mmap() failed to set ->vm_ops, mmap_region() will set it to > > dummy_vm_ops. This way we will have non-NULL ->vm_ops for all VMAs. > > Is there a smaller, simpler fix which we can use for backporting > purposes and save the larger rework for development kernels? Why cannot we simply keep anon vma with null vm_ops and set dummy_vm_ops for all users who do not initialize it in their mmap callbacks? Basically have a sanity check&fixup in call_mmap? -- Michal Hocko SUSE Labs
