Chengguang Xu wrote on Mon, Dec 07, 2020: > > , VM_MAYWRITE is set anytime we have a shared map where file has > > been opened read-write, which seems to be what you want with regards to > > protecting from mprotect calls. > > > > How about simply changing check from WRITE to MAYWRITE? > > It would be fine and based on the code in do_mmap(), it seems we even don't > need extra check here. The condition (vma->vm_flags & VM_SHARED) will be > enough. > Am I missing something?
VM_MAYWRITE is unset if the file hasn't been open for writing (in which case the mapping can't be mprotect()ed to writable map), so checking it is a bit more efficient. Anyway I'd like to obsolete the writeback fid uses now that fids have a refcount (this usecase can be a simple refcount increase), in which case efficiency is less of a problem, but we're not there yet... Please resend with MAYWRITE if you want authorship and I'll try to take some time to test incl. the mprotect usecase. -- Dominique
