On Fri, Oct 18, 2024 at 01:22:35PM +0200, Roberto Sassu wrote:
> On Fri, 2024-10-18 at 14:05 +0300, Kirill A. Shutemov wrote:
> > On Fri, Oct 18, 2024 at 12:00:22PM +0100, Lorenzo Stoakes wrote:
> > > + Liam, Jann
> > >
> > > On Fri, Oct 18, 2024 at 01:49:06PM +0300, Kirill A. Shutemov wrote:
> > > > On Fri, Oct 18, 2024 at 11:24:06AM +0200, Roberto Sassu wrote:
> > > > > Probably it is hard, @Kirill would there be any way to safely move
> > > > > security_mmap_file() out of the mmap_lock lock?
> > > >
> > > > What about something like this (untested):
> > > >
> > > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > > index dd4b35a25aeb..03473e77d356 100644
> > > > --- a/mm/mmap.c
> > > > +++ b/mm/mmap.c
> > > > @@ -1646,6 +1646,26 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
> > > > if (pgoff + (size >> PAGE_SHIFT) < pgoff)
> > > > return ret;
> > > >
> > > > + if (mmap_read_lock_killable(mm))
> > > > + return -EINTR;
> > > > +
> > > > + vma = vma_lookup(mm, start);
> > > > +
> > > > + if (!vma || !(vma->vm_flags & VM_SHARED)) {
> > > > + mmap_read_unlock(mm);
> > > > + return -EINVAL;
> > > > + }
> > > > +
> > > > + file = get_file(vma->vm_file);
> > > > +
> > > > + mmap_read_unlock(mm);
> > > > +
> > > > + ret = security_mmap_file(vma->vm_file, prot, flags);
> > >
> > > Accessing VMA fields without any kind of lock is... very much not advised.
> > >
> > > I'm guessing you meant to say:
> > >
> > > ret = security_mmap_file(file, prot, flags);
> > >
> > > Here? :)
> >
> > Sure. My bad.
> >
> > Patch with all fixups:
>
> Thanks a lot! Let's wait a bit until the others have a chance to
> comment. Meanwhile, I will test it.
>
> Do you want me to do the final patch, or will you be proposing it?
You can post it if it works:
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
--
Kiryl Shutsemau / Kirill A. Shutemov
