vm audit: add VM_DONTEXPAND to mmap for drivers that need it

Drivers that register a ->fault handler, but do not range-check the
offset argument, must set VM_DONTEXPAND in the vm_flags in order to
prevent an expanding mremap from overflowing the resource.

I've audited the tree and attempted to fix these problems (usually by
adding VM_DONTEXPAND where it is not obvious).

Signed-off-by: Nick Piggin <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/drm/drm_vm.c

···
 	vma->vm_ops = &drm_vm_dma_ops;
 
 	vma->vm_flags |= VM_RESERVED;	/* Don't swap */
+	vma->vm_flags |= VM_DONTEXPAND;
 
 	vma->vm_file = filp;	/* Needed for drm_vm_open() */
 	drm_vm_open_locked(vma);
···
 		return -EINVAL;	/* This should never happen. */
 	}
 	vma->vm_flags |= VM_RESERVED;	/* Don't swap */
+	vma->vm_flags |= VM_DONTEXPAND;
 
 	vma->vm_file = filp;	/* Needed for drm_vm_open() */
 	drm_vm_open_locked(vma);

drivers/char/mspec.c

···
 	vdata->refcnt = ATOMIC_INIT(1);
 	vma->vm_private_data = vdata;
 
-	vma->vm_flags |= (VM_IO | VM_RESERVED | VM_PFNMAP);
+	vma->vm_flags |= (VM_IO | VM_RESERVED | VM_PFNMAP | VM_DONTEXPAND);
 	if (vdata->type == MSPEC_FETCHOP || vdata->type == MSPEC_UNCACHED)
 		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_ops = &mspec_vm_ops;

fs/ncpfs/mmap.c

···
 	pos = vmf->pgoff << PAGE_SHIFT;
 
 	count = PAGE_SIZE;
-	if ((unsigned long)vmf->virtual_address + PAGE_SIZE > area->vm_end) {
-		WARN_ON(1); /* shouldn't happen? */
-		count = area->vm_end - (unsigned long)vmf->virtual_address;
-	}
 	/* what we can read in one go */
 	bufsize = NCP_SERVER(inode)->buffer_size;
 

kernel/relay.c

···
 		return -EINVAL;
 
 	vma->vm_ops = &relay_file_mmap_ops;
+	vma->vm_flags |= VM_DONTEXPAND;
 	vma->vm_private_data = buf;
 	buf->chan->cb->buf_mapped(buf, filp);
 

mm/mmap.c

···
 	vma->vm_start = addr;
 	vma->vm_end = addr + len;
 
-	vma->vm_flags = vm_flags | mm->def_flags;
+	vma->vm_flags = vm_flags | mm->def_flags | VM_DONTEXPAND;
 	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 
 	vma->vm_ops = &special_mapping_vmops;

sound/oss/via82cxxx_audio.c

···
 {
 	struct via_info *card = vma->vm_private_data;
 	struct via_channel *chan = &card->ch_out;
+	unsigned long max_bufs;
 	struct page *dmapage;
 	unsigned long pgoff;
 	int rd, wr;
···
 	rd = card->ch_in.is_mapped;
 	wr = card->ch_out.is_mapped;
 
-#ifndef VIA_NDEBUG
-	{
-	unsigned long max_bufs = chan->frag_number;
-	if (rd && wr) max_bufs *= 2;
-	/* via_dsp_mmap() should ensure this */
-	assert (pgoff < max_bufs);
-	}
-#endif
+	max_bufs = chan->frag_number;
+	if (rd && wr)
+		max_bufs *= 2;
+	if (pgoff >= max_bufs)
+		return NOPAGE_SIGBUS;
 
 	/* if full-duplex (read+write) and we have two sets of bufs,
 	 * then the playback buffers come first, sez soundcard.c */

sound/usb/usx2y/usX2Yhwdep.c

···
 		us428->us428ctls_sharedmem->CtlSnapShotLast = -2;
 	}
 	area->vm_ops = &us428ctls_vm_ops;
-	area->vm_flags |= VM_RESERVED;
+	area->vm_flags |= VM_RESERVED | VM_DONTEXPAND;
 	area->vm_private_data = hw->private_data;
 	return 0;
 }

sound/usb/usx2y/usx2yhwdeppcm.c

···
 		return -ENODEV;
 	}
 	area->vm_ops = &snd_usX2Y_hwdep_pcm_vm_ops;
-	area->vm_flags |= VM_RESERVED;
+	area->vm_flags |= VM_RESERVED | VM_DONTEXPAND;
 	area->vm_private_data = hw->private_data;
 	return 0;
 }