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([2001:b07:6468:f312:459f:99a9:39f1:65ba]) by smtp.gmail.com with ESMTPSA id b63sm6832818wmb.40.2019.11.27.08.40.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Nov 2019 08:40:55 -0800 (PST) Subject: Re: [PATCH 1/1] powerpc/kvm/book3s: Fixes possible 'use after release' of kvm To: Leonardo Bras , Sean Christopherson , kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paul Mackerras , Benjamin Herrenschmidt , Michael Ellerman , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= References: <20191126175212.377171-1-leonardo@linux.ibm.com> From: Paolo Bonzini Message-ID: Date: Wed, 27 Nov 2019 17:40:54 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191126175212.377171-1-leonardo@linux.ibm.com> Content-Language: en-US X-MC-Unique: 3Dl_abkKPnuL2uc9XfNy1w-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/11/19 18:52, Leonardo Bras wrote: > Fixes a possible 'use after free' of kvm variable. > It does use mutex_unlock(&kvm->lock) after possible freeing a variable > with kvm_put_kvm(kvm). > > Signed-off-by: Leonardo Bras > --- > arch/powerpc/kvm/book3s_64_vio.c | 3 +-- > virt/kvm/kvm_main.c | 8 ++++---- > 2 files changed, 5 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c > index 5834db0a54c6..a402ead833b6 100644 > --- a/arch/powerpc/kvm/book3s_64_vio.c > +++ b/arch/powerpc/kvm/book3s_64_vio.c > @@ -316,14 +316,13 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm, > > if (ret >= 0) > list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables); > - else > - kvm_put_kvm(kvm); > > mutex_unlock(&kvm->lock); > > if (ret >= 0) > return ret; > > + kvm_put_kvm(kvm); > kfree(stt); > fail_acct: > account_locked_vm(current->mm, kvmppc_stt_pages(npages), false); This part is a good change, as it makes the code clearer. The virt/kvm/kvm_main.c bits, however, are not necessary as explained by Sean. Paolo > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 13efc291b1c7..f37089b60d09 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2744,10 +2744,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) > /* Now it's all set up, let userspace reach it */ > kvm_get_kvm(kvm); > r = create_vcpu_fd(vcpu); > - if (r < 0) { > - kvm_put_kvm(kvm); > + if (r < 0) > goto unlock_vcpu_destroy; > - } > > kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu; > > @@ -2771,6 +2769,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) > mutex_lock(&kvm->lock); > kvm->created_vcpus--; > mutex_unlock(&kvm->lock); > + if (r < 0) > + kvm_put_kvm(kvm); > return r; > } > > @@ -3183,10 +3183,10 @@ static int kvm_ioctl_create_device(struct kvm *kvm, > kvm_get_kvm(kvm); > ret = anon_inode_getfd(ops->name, &kvm_device_fops, dev, O_RDWR | O_CLOEXEC); > if (ret < 0) { > - kvm_put_kvm(kvm); > mutex_lock(&kvm->lock); > list_del(&dev->vm_node); > mutex_unlock(&kvm->lock); > + kvm_put_kvm(kvm); > ops->destroy(dev); > return ret; > } >