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 <leona...@linux.ibm.com>
> ---
> 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;
> }
>
