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Message-ID: <aa600c47-d6d5-161d-419d-51ac30d67ee4@redhat.com>
Date: Wed, 23 Aug 2017 10:25:41 +0200
From: David Hildenbrand <david@...hat.com>
To: Paul Mackerras <paulus@...abs.org>,
Nixiaoming <nixiaoming@...wei.com>
Cc: "agraf@...e.com" <agraf@...e.com>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"rkrcmar@...hat.com" <rkrcmar@...hat.com>,
"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
"mpe@...erman.id.au" <mpe@...erman.id.au>,
"kvm-ppc@...r.kernel.org" <kvm-ppc@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr_tce
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@...wei.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@...hat.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@...hat.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
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