Re: [PATCH v15 06/11] mm: introduce memfd_secret system call to create "secret" memory areas

On Wed, Jan 20, 2021 at 08:06:07PM +0200, Mike Rapoport wrote:

+static struct page *secretmem_alloc_page(gfp_t gfp) +{

• /*

• * FIXME: use a cache of large pages to reduce the direct map
  

• * fragmentation
  

• */
  

• return alloc_page(gfp);

+}

+static vm_fault_t secretmem_fault(struct vm_fault *vmf) +{

• struct address_space *mapping = vmf->vma->vm_file->f_mapping;
• struct inode *inode = file_inode(vmf->vma->vm_file);
• pgoff_t offset = vmf->pgoff;
• unsigned long addr;
• struct page *page;
• int err;
• if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))

• return vmf_error(-EINVAL);
  

+retry:

• page = find_lock_page(mapping, offset);
• if (!page) {

• page = secretmem_alloc_page(vmf->gfp_mask);
  

• if (!page)
  

• 	return VM_FAULT_OOM;
  

• err = set_direct_map_invalid_noflush(page, 1);
  

• if (err)
  

• 	return vmf_error(err);
  

Haven't we leaked the page at this point?

• __SetPageUptodate(page);
  

• err = add_to_page_cache(page, mapping, offset, vmf->gfp_mask);
  

At this point, doesn't the page contain data from the last person to use the page? ie we've leaked data to this process? I don't see anywhere that we write data to the page.