diff mbox

答复: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr_tce

Message ID E490CD805F7529488761C40FD9D26EF1299B4859@DGGEMA505-MBX.china.huawei.com (mailing list archive)
State Superseded
Delegated to: Paul Mackerras
Headers show

Commit Message

Xiaoming Ni Aug. 23, 2017, 10:17 a.m. UTC 
>On 23.08.2017 08:06, Paul Mackerras wrote:

>> On Wed, Aug 23, 2017 at 01:43:08AM +0000, Nixiaoming wrote:

>>>> On 22.08.2017 17:15, David Hildenbrand wrote:

>>>>> On 22.08.2017 16:28, nixiaoming wrote:

>>>>>> miss kfree(stt) when anon_inode_getfd return fail so add check 

>>>>>> anon_inode_getfd return val, and kfree stt

>>>>>>

>>>>>> Signed-off-by: nixiaoming <nixiaoming@huawei.com>

>>>>>> ---

>>>>>>  arch/powerpc/kvm/book3s_64_vio.c | 5 ++++-

>>>>>>  1 file changed, 4 insertions(+), 1 deletion(-)

>>>>>>

>>>>>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c 

>>>>>> b/arch/powerpc/kvm/book3s_64_vio.c

>>>>>> index a160c14..a0b4459 100644

>>>>>> --- a/arch/powerpc/kvm/book3s_64_vio.c

>>>>>> +++ b/arch/powerpc/kvm/book3s_64_vio.c

>>>>>> @@ -341,8 +341,11 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm 

>>>>>> *kvm,

>>>>>>  

>>>>>>  	mutex_unlock(&kvm->lock);

>>>>>>  

>>>>>> -	return anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,

>>>>>> +	ret = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,

>>>>>>  				stt, O_RDWR | O_CLOEXEC);

>>>>>> +	if (ret < 0)

>>>>>> +		goto fail;

>>>>>> +	return ret;

>>>>>>  

>>>>>>  fail:

>>>>>>  	if (stt) {

>>>>>>

>>>>>

>>>>>

>>>>> stt has already been added to kvm->arch.spapr_tce_tables, so freeing 

>>>>> it is evil IMHO. I don't know that code, so I don't know if there is 

>>>>> some other place that will make sure that everything in

>>>>> kvm->arch.spapr_tce_tables will properly get freed, even when no 

>>>>> kvm->release

>>>>> function has been called (kvm_spapr_tce_release).

>>>>>

>>>>

>>>> If it is really not freed, than also kvm_put_kvm(stt->kvm) is missing.

>>>>

>>>> -- 

>>>>

>>>> Thanks,

>>>>

>>>> David

>>>>

>>>

>>> if (!stt) return -ENOMEM;

>>> kvm_get_kvm(kvm);

>>> if anon_inode_getfd return -ENOMEM

>>> The user can not determine whether kvm_get_kvm has been called

>>> so need add kvm_pet_kvm when anon_inode_getfd fail

>>>

>>> stt has already been added to kvm->arch.spapr_tce_tables,

>>> but if anon_inode_getfd fail, stt is unused val, 

>>> so call list_del_rcu, and  free as quickly as possible

>>>

>>> new patch:

>>>

>>> ---

>>>  arch/powerpc/kvm/book3s_64_vio.c | 10 +++++++++-

>>>  1 file changed, 9 insertions(+), 1 deletion(-)

>>>

>>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c

>>> index a160c14..e2228f1 100644

>>> --- a/arch/powerpc/kvm/book3s_64_vio.c

>>> +++ b/arch/powerpc/kvm/book3s_64_vio.c

>>> @@ -341,8 +341,16 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

>>>

>>>         mutex_unlock(&kvm->lock);

>>>

>>> -       return anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,

>>> +       ret = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,

>>>                                 stt, O_RDWR | O_CLOEXEC);

>>> +       if (ret < 0) {

>>> +               mutex_lock(&kvm->lock);

>>> +               list_del_rcu(&stt->list);

>

>... don't we have to take care of rcu synchronization before freeing it?

>

>>> +               mutex_unlock(&kvm->lock);

>>> +               kvm_put_kvm(kvm);

>>> +               goto fail;

>>> +       }

>>> +       return ret;

>

>of simply

>

>if (!ret)

>	return 0;

>

>mutex_lock(&kvm->lock);

>list_del_rcu(&stt->list);

>mutex_unlock(&kvm->lock);

>kvm_put_kvm(kvm);

>

>

>> 

>> It seems to me that it would be better to do the anon_inode_getfd()

>> call before the kvm_get_kvm() call, and go to the fail label if it

>> fails.

>

>I would have suggested to not add it to the list before it has been

>fully created (so nobody can have access to it). But I guess than we

>need another level of protection(e.g. kvm->lock).

>

>Am I missing something, or is kvm_vm_ioctl_create_spapr_tce() racy?

>

>The -EBUSY check is done without any locking, so two parallel creators

>could create an inconsistency, no? Shouldn't this all be protected by

>kvm->lock?

>

>> 

>> Paul.

>> 

>

>Independent of the fix, I'd suggest the following cleanup.

>

>

>From 979f55083ee965e25827a8743e8a9fdb85231a6f Mon Sep 17 00:00:00 2001

>From: David Hildenbrand <david@redhat.com>

>Date: Wed, 23 Aug 2017 10:08:58 +0200

>Subject: [PATCH v1 1/1] KVM: PPC: cleanup kvm_vm_ioctl_create_spapr_tce

>

>Let's simplify error handling.

>

>Signed-off-by: David Hildenbrand <david@redhat.com>

>---

> arch/powerpc/kvm/book3s_64_vio.c | 29 +++++++++++------------------

> 1 file changed, 11 insertions(+), 18 deletions(-)

>

>diff --git a/arch/powerpc/kvm/book3s_64_vio.c

>b/arch/powerpc/kvm/book3s_64_vio.c

>index a160c14304eb..6bac49292296 100644

>--- a/arch/powerpc/kvm/book3s_64_vio.c

>+++ b/arch/powerpc/kvm/book3s_64_vio.c

>@@ -295,8 +295,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

> {

> 	struct kvmppc_spapr_tce_table *stt = NULL;

> 	unsigned long npages, size;

>-	int ret = -ENOMEM;

>-	int i;

>+	int i, ret;

>

> 	if (!args->size)

> 		return -EINVAL;

>@@ -310,16 +309,13 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

> 	size = _ALIGN_UP(args->size, PAGE_SIZE >> 3);

> 	npages = kvmppc_tce_pages(size);

> 	ret = kvmppc_account_memlimit(kvmppc_stt_pages(npages), true);

>-	if (ret) {

>-		stt = NULL;

>-		goto fail;

>-	}

>+	if (ret)

>+		return ret;

>

>-	ret = -ENOMEM;

> 	stt = kzalloc(sizeof(*stt) + npages * sizeof(struct page *),

> 		      GFP_KERNEL);

> 	if (!stt)

>-		goto fail;

>+		return -ENOMEM;

>

> 	stt->liobn = args->liobn;

> 	stt->page_shift = args->page_shift;

>@@ -331,7 +327,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

> 	for (i = 0; i < npages; i++) {

> 		stt->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);

> 		if (!stt->pages[i])

>-			goto fail;

>+			goto fail_free;

> 	}

>

> 	kvm_get_kvm(kvm);

>@@ -344,15 +340,12 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,

> 	return anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,

> 				stt, O_RDWR | O_CLOEXEC);

>

>-fail:

>-	if (stt) {

>-		for (i = 0; i < npages; i++)

>-			if (stt->pages[i])

>-				__free_page(stt->pages[i]);

>-

>-		kfree(stt);

>-	}

>-	return ret;

>+fail_free:

>+	for (i = 0; i < npages; i++)

>+		if (stt->pages[i])

>+			__free_page(stt->pages[i]);

>+	kfree(stt);

>+	return -ENOMEM;

> }

>

> static void kvmppc_clear_tce(struct iommu_table *tbl, unsigned long entry)

>-- 

>2.13.5

>

>

>-- 

>

>Thanks,

>

>David

>


Update patch based on advice from David Hildenbrand and Paul Mackerras

---
 arch/powerpc/kvm/book3s_64_vio.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--
diff mbox

Patch

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index a160c14..517594a 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -334,16 +334,21 @@  long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
 			goto fail;
 	}
 
-	kvm_get_kvm(kvm);
-
 	mutex_lock(&kvm->lock);
 	list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables);
 
 	mutex_unlock(&kvm->lock);
 
-	return anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,
+	ret = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops,
 				stt, O_RDWR | O_CLOEXEC);
-
+	if (ret >= 0) {
+		kvm_get_kvm(kvm);
+		return ret;
+	}
+	mutex_lock(&kvm->lock);
+	list_del_rcu(&stt->list);
+	mutex_unlock(&kvm->lock);
+	synchronize_rcu();
 fail:
 	if (stt) {
 		for (i = 0; i < npages; i++)