[PATCH] rmap: validate pointer in anon_vma_clone

[PATCH] rmap: validate pointer in anon_vma_clone

[Leon Ma]

If memory allocation failed in first loop, root will be NULL and
will lead to kernel panic.

Signed-off-by: Leon Ma <xindong.ma@intel.com>
---
 mm/rmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e773..6e53aed 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -246,8 +246,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 
 		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
 		if (unlikely(!avc)) {
-			unlock_anon_vma_root(root);
-			root = NULL;
+			if (!root) {
+				unlock_anon_vma_root(root);
+				root = NULL;
+			}
 			avc = anon_vma_chain_alloc(GFP_KERNEL);
 			if (!avc)
 				goto enomem_failure;
-- 
1.7.9.5

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RE: [PATCH] rmap: validate pointer in anon_vma_clone

[Ma, Xindong]

Sorry, my fault. It's already validated in unlock_anon_vma_root().


BR
Leon


-----Original Message-----
From: Ma, Xindong 
Sent: Wednesday, May 07, 2014 10:32 AM
To: akpm@linux-foundation.org; iamjoonsoo.kim@lge.com; n-horiguchi@ah.jp.nec.com; kirill.shutemov@linux.intel.com; gorcunov@gmail.com; linux-mm@kvack.org; linux-kernel@vger.kernel.org
Cc: Ma, Xindong
Subject: [PATCH] rmap: validate pointer in anon_vma_clone

If memory allocation failed in first loop, root will be NULL and will lead to kernel panic.

Signed-off-by: Leon Ma <xindong.ma@intel.com>
---
 mm/rmap.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 9c3e773..6e53aed 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -246,8 +246,10 @@ int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
 
 		avc = anon_vma_chain_alloc(GFP_NOWAIT | __GFP_NOWARN);
 		if (unlikely(!avc)) {
-			unlock_anon_vma_root(root);
-			root = NULL;
+			if (!root) {
+				unlock_anon_vma_root(root);
+				root = NULL;
+			}
 			avc = anon_vma_chain_alloc(GFP_KERNEL);
 			if (!avc)
 				goto enomem_failure;
--
1.7.9.5

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Re: [PATCH] rmap: validate pointer in anon_vma_clone

[Jianyu Zhan]

On Wed, May 7, 2014 at 10:32 AM, Leon Ma <xindong.ma@intel.com> wrote:
> If memory allocation failed in first loop, root will be NULL and
> will lead to kernel panic.

Hello, Leon,

I am afraid not.  unlock_anon_vma_root() has a sanity check NULLness of root,
so it is impossible to panic for a dangling root pointer.



Thanks,
Jianyu Zhan

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