Re: [PATCH 1/8] mm/fs: don't allow writes to immutable files

Darrick J. Wong
2019-06-10T04:41:53Z

On Sun, Jun 09, 2019 at 09:51:45PM -0400, Theodore Ts'o wrote:
> On Wed, Apr 17, 2019 at 12:04:33PM -0700, Darrick J. Wong wrote:
> > diff --git a/mm/memory.c b/mm/memory.c
> > index ab650c21bccd..dfd5eba278d6 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2149,6 +2149,9 @@ static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
> >
> > vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
> >
> > + if (vmf->vma->vm_file && IS_IMMUTABLE(file_inode(vmf->vma->vm_file)))
> > + return VM_FAULT_SIGBUS;
> > +
> > ret = vmf->vma->vm_ops->page_mkwrite(vmf);
> > /* Restore original flags so that caller is not surprised */
> > vmf->flags = old_flags;
>
> Shouldn't this check be moved before the modification of vmf->flags?
> It looks like do_page_mkwrite() isn't supposed to be returning with
> vmf->flags modified, lest "the caller gets surprised".

Yeah, I think that was a merge error during a rebase... :(

Er ... if you're still planning to take this patch through your tree,
can you move it to above the "vmf->flags = FAULT_FLAG_WRITE..." ?

--D

> - Ted