linux-kernel - Re:Re: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr

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Date:   Wed, 23 Aug 2017 01:43:08 +0000
From:   Nixiaoming <nixiaoming@...wei.com>
To:     David Hildenbrand <david@...hat.com>,
        "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>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>
CC:     "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:Re: [PATCH] fix memory leak on kvm_vm_ioctl_create_spapr_tce

>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);
+               mutex_unlock(&kvm->lock);
+               kvm_put_kvm(kvm);
+               goto fail;
+       }
+       return ret;

 fail:
        if (stt) {
-- 
2.11.0.1