* Suren Baghdasaryan <surenb@xxxxxxxxxx> [230801 18:07]:
> While it's not strictly necessary to lock a newly created vma before
> adding it into the vma tree (as long as no further changes are performed
> to it), it seems like a good policy to lock it and prevent accidental
> changes after it becomes visible to the page faults. Lock the vma before
> adding it into the vma tree.
>
> Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/mmap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3937479d0e07..850a39dee075 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -412,6 +412,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
> if (vma_iter_prealloc(&vmi))
> return -ENOMEM;
>
> + vma_start_write(vma);
> +
> if (vma->vm_file) {
> mapping = vma->vm_file->f_mapping;
> i_mmap_lock_write(mapping);
> @@ -477,7 +479,8 @@ static inline void vma_prepare(struct vma_prepare *vp)
> vma_start_write(vp->vma);
> if (vp->adj_next)
> vma_start_write(vp->adj_next);
> - /* vp->insert is always a newly created VMA, no need for locking */
> + if (vp->insert)
> + vma_start_write(vp->insert);
> if (vp->remove)
> vma_start_write(vp->remove);
> if (vp->remove2)
> @@ -3098,6 +3101,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
> vma->vm_pgoff = addr >> PAGE_SHIFT;
> vm_flags_init(vma, flags);
> vma->vm_page_prot = vm_get_page_prot(flags);
> + vma_start_write(vma);
> if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
> goto mas_store_fail;
>
> @@ -3345,7 +3349,6 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
> get_file(new_vma->vm_file);
> if (new_vma->vm_ops && new_vma->vm_ops->open)
> new_vma->vm_ops->open(new_vma);
> - vma_start_write(new_vma);
> if (vma_link(mm, new_vma))
> goto out_vma_link;
> *need_rmap_locks = false;
> --
> 2.41.0.585.gd2178a4bd4-goog
>
