linux-kernel - Re: [PATCH] mm: mmap: Check all failures before set values

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Date:	Mon, 24 Aug 2015 14:25:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	gang.chen.5i5j@...com, kirill.shutemov@...ux.intel.com,
	riel@...hat.com, sasha.levin@...cle.com, gang.chen.5i5j@...il.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: mmap: Check all failures before set values

On Mon, 24 Aug 2015 13:32:13 +0200 Michal Hocko <mhocko@...nel.org> wrote:

> On Mon 24-08-15 00:59:39, gang.chen.5i5j@...com wrote:
> > From: Chen Gang <gang.chen.5i5j@...il.com>
> > 
> > When failure occurs and return, vma->vm_pgoff is already set, which is
> > not a good idea.
> 
> Why? The vma is not inserted anywhere and the failure path is supposed
> to simply free the vma.

Yes, it's pretty marginal but I suppose the code is a bit better with
the patch than without.  I did this:


From: Chen Gang <gang.chen.5i5j@...il.com>
Subject: mm/mmap.c:insert_vm_struct(): check for failure before setting values

There's no point in initializing vma->vm_pgoff if the insertion attempt
will be failing anyway.  Run the checks before performing the initialization.

Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
Cc: Michal Hocko <mhocko@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/mmap.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff -puN mm/mmap.c~mm-mmap-check-all-failures-before-set-values mm/mmap.c
--- a/mm/mmap.c~mm-mmap-check-all-failures-before-set-values
+++ a/mm/mmap.c
@@ -2859,6 +2859,13 @@ int insert_vm_struct(struct mm_struct *m
 	struct vm_area_struct *prev;
 	struct rb_node **rb_link, *rb_parent;
 
+	if (find_vma_links(mm, vma->vm_start, vma->vm_end,
+			   &prev, &rb_link, &rb_parent))
+		return -ENOMEM;
+	if ((vma->vm_flags & VM_ACCOUNT) &&
+	     security_vm_enough_memory_mm(mm, vma_pages(vma)))
+		return -ENOMEM;
+
 	/*
 	 * The vm_pgoff of a purely anonymous vma should be irrelevant
 	 * until its first write fault, when page's anon_vma and index
@@ -2875,12 +2882,6 @@ int insert_vm_struct(struct mm_struct *m
 		BUG_ON(vma->anon_vma);
 		vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
 	}
-	if (find_vma_links(mm, vma->vm_start, vma->vm_end,
-			   &prev, &rb_link, &rb_parent))
-		return -ENOMEM;
-	if ((vma->vm_flags & VM_ACCOUNT) &&
-	     security_vm_enough_memory_mm(mm, vma_pages(vma)))
-		return -ENOMEM;
 
 	vma_link(mm, vma, prev, rb_link, rb_parent);
 	return 0;
_


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