From: Alexey Kardashevskiy Date: Thu, 21 Feb 2019 03:44:14 +0000 (+1100) Subject: KVM: PPC: Book3S: Improve KVM reference counting X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=716cb1160819721c39f807e103d9c307dbca2cf4;p=linux.git KVM: PPC: Book3S: Improve KVM reference counting The anon fd's ops releases the KVM reference in the release hook. However we reference the KVM object after we create the fd so there is small window when the release function can be called and dereferenced the KVM object which potentially may free it. It is not a problem at the moment as the file is created and KVM is referenced under the KVM lock and the release function obtains the same lock before dereferencing the KVM (although the lock is not held when calling kvm_put_kvm()) but it is potentially fragile against future changes. This references the KVM object before creating a file. Signed-off-by: Alexey Kardashevskiy Signed-off-by: Paul Mackerras --- diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c index 6630dde566680..f02b049737109 100644 --- a/arch/powerpc/kvm/book3s_64_vio.c +++ b/arch/powerpc/kvm/book3s_64_vio.c @@ -337,14 +337,15 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm, } } + kvm_get_kvm(kvm); if (!ret) ret = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops, stt, O_RDWR | O_CLOEXEC); - if (ret >= 0) { + if (ret >= 0) list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables); - kvm_get_kvm(kvm); - } + else + kvm_put_kvm(kvm); mutex_unlock(&kvm->lock);