On Tue, Aug 6, 2024 at 2:28 PM Pedro Falcato <pedro.falcato@xxxxxxxxx> wrote:
>
> Delegate all can_modify checks to the proper places. Unmap checks are
> done in do_unmap (et al).
>
> This patch allows for mremap partial failure in certain cases (for
> instance, when destination VMAs aren't sealed, but the source VMA is).
> It shouldn't be too troublesome, as you'd need to go out of your way to
> do illegal operations on a VMA.
>
> Signed-off-by: Pedro Falcato <pedro.falcato@xxxxxxxxx>
> ---
> mm/mremap.c | 33 +++++++--------------------------
> 1 file changed, 7 insertions(+), 26 deletions(-)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index e7ae140fc64..8af877d7bb0 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -676,6 +676,9 @@ static unsigned long move_vma(struct vm_area_struct *vma,
> if (unlikely(flags & MREMAP_DONTUNMAP))
> to_account = new_len;
>
> + if (!can_modify_vma(vma))
> + return -EPERM;
> +
I m not 100% sure, but I suspect you don't need this check? Is
vma_to_resize already checking the src address ?
PS. Is it possible to consolidate all the related changes (except the
fix for madvise) to a single commit ?
It would be easier to look for dependency, e.g. the remap depends on munmap().
Also selftest is helpful to prove the correctness of the change. (And
I can also test it)
> if (vma->vm_ops && vma->vm_ops->may_split) {
> if (vma->vm_start != old_addr)
> err = vma->vm_ops->may_split(vma, old_addr);
> @@ -821,6 +824,10 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> if (!vma)
> return ERR_PTR(-EFAULT);
>
> + /* Don't allow vma expansion when it has already been sealed */
> + if (!can_modify_vma(vma))
> + return ERR_PTR(-EPERM);
> +
> /*
> * !old_len is a special case where an attempt is made to 'duplicate'
> * a mapping. This makes no sense for private mappings as it will
> @@ -902,19 +909,6 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
> return -ENOMEM;
>
> - /*
> - * In mremap_to().
> - * Move a VMA to another location, check if src addr is sealed.
> - *
> - * Place can_modify_mm here because mremap_to()
> - * does its own checking for address range, and we only
> - * check the sealing after passing those checks.
> - *
> - * can_modify_mm assumes we have acquired the lock on MM.
> - */
> - if (unlikely(!can_modify_mm(mm, addr, addr + old_len)))
> - return -EPERM;
> -
> if (flags & MREMAP_FIXED) {
> /*
> * In mremap_to().
> @@ -1079,19 +1073,6 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> goto out;
> }
>
> - /*
> - * Below is shrink/expand case (not mremap_to())
> - * Check if src address is sealed, if so, reject.
> - * In other words, prevent shrinking or expanding a sealed VMA.
> - *
> - * Place can_modify_mm here so we can keep the logic related to
> - * shrink/expand together.
> - */
> - if (unlikely(!can_modify_mm(mm, addr, addr + old_len))) {
> - ret = -EPERM;
> - goto out;
> - }
> -
> /*
> * Always allow a shrinking remap: that just unmaps
> * the unnecessary pages..
> --
> 2.46.0
>
