On Mon, Nov 1, 2021 at 8:16 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote: > > > > > > FILE *vm_file = vma->vm_file; /* no checking is needed, vma from > > > parameter which is not NULL */ > > > if (vm_file) > > > bpf_d_path(&vm_file->f_path, path, sizeof(path)); > > > > That should work. > > The verifier can achieve that by marking certain fields as PTR_TO_BTF_ID_OR_NULL > > instead of PTR_TO_BTF_ID while walking such pointers. > > And then disallow pointer arithmetic on PTR_TO_BTF_ID_OR_NULL until it > > goes through 'if (Rx == NULL)' check inside the program and gets converted to > > PTR_TO_BTF_ID. > > Initially we can hard code such fields via BTF_ID(struct, file) macro.' > > So any pointer that results into a 'struct file' pointer will be > > PTR_TO_BTF_ID_OR_NULL. > > Can we just require all helpers to check NULL if they accept > PTR_TO_BTF_ID? It's always been a case that PTR_TO_BTF_ID can be null. > We should audit all the helpers with ARG_PTR_TO_BTF_ID and ensure they > do proper validation, of course. > > Or am I missing the essence of the issue? It's not a pointer dereference. It's math on the pointer. The &vm_file->f_path part. The helper can check that it's [0, few_pages] and declare it's bad. I guess we can do that and only do what I proposed for "more than a page" math on the pointer. Or even disallow "add more than a page offset to PTR_TO_BTF_ID" for now, since it will cover 99% of the cases.
