On Tue, Sep 29, 2020 at 6:20 PM Jann Horn <jannh@xxxxxxxxxx> wrote: > create_elf_tables() runs after setup_new_exec(), so other tasks can > already access our new mm and do things like process_madvise() on it. > (At the time I'm writing this commit, process_madvise() is not in mainline > yet, but has been in akpm's tree for some time.) > > While I believe that there are currently no APIs that would actually allow > another process to mess up our VMA tree (process_madvise() is limited to > MADV_COLD and MADV_PAGEOUT, and uring and userfaultfd cannot reach an mm > under which no syscalls have been executed yet), this seems like an > accident waiting to happen. > > Let's make sure that we always take the mmap lock around GUP paths as long > as another process might be able to see the mm. > > (Yes, this diff looks suspicious because we drop the lock before doing > anything with `vma`, but that's because we actually don't do anything with > it apart from the NULL check.) > > Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> Thanks for these cleanups :) Acked-by: Michel Lespinasse <walken@xxxxxxxxxx>
