linux-kernel - [PATCH v3 5/6] mm: always lock new vma before inserting into vma tree

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Date:   Thu,  3 Aug 2023 10:26:50 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     torvalds@...ux-foundation.org, jannh@...gle.com,
        willy@...radead.org, liam.howlett@...cle.com, david@...hat.com,
        peterx@...hat.com, ldufour@...ux.ibm.com, vbabka@...e.cz,
        michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        hannes@...xchg.org, dave@...olabs.net, hughd@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v3 5/6] mm: always lock new vma before inserting into vma tree

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@...gle.com>
Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 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