Messages in this thread | | | Date | Sun, 16 Feb 2020 08:46:50 +0200 | From | Mike Rapoport <> | Subject | Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas |
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On Wed, Feb 12, 2020 at 02:10:29PM -0700, Jonathan Corbet wrote: > On Thu, 30 Jan 2020 18:23:41 +0200 > Mike Rapoport <rppt@kernel.org> wrote: > > > Hi, > > > > This is essentially a resend of my attempt to implement "secret" mappings > > using a file descriptor [1]. > > So one little thing I was curious about as I read through the patch... > > > +static int secretmem_check_limits(struct vm_fault *vmf) > > +{ > > + struct secretmem_state *state = vmf->vma->vm_file->private_data; > > + struct inode *inode = file_inode(vmf->vma->vm_file); > > + unsigned long limit; > > + > > + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) > > + return -EINVAL; > > + > > + limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT; > > + if (state->nr_pages + 1 >= limit) > > + return -EPERM; > > + > > + return 0; > > +} > > If I'm not mistaken, this means each memfd can be RLIMIT_MEMLOCK in length, > with no global limit on the number of locked pages. What's keeping me from > creating 1000 of these things and locking down lots of RAM?
Indeed, it's possible to lock down RLIMIT_MEMLOCK * RLIMIT_NOFILE of RAM with this implementation, thanks for catching this.
I'll surely update the resource limiting once we've settle on the API selection :)
> Thanks, > > jon >
-- Sincerely yours, Mike.
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