From 5593473a1e6c743764b08e3b6071cb43b5cfa6c4 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 6 Apr 2022 13:13:42 -0400 Subject: [PATCH] KVM: avoid NULL pointer dereference in kvm_dirty_ring_push kvm_vcpu_release() will call kvm_dirty_ring_free(), freeing ring->dirty_gfns and setting it to NULL. Afterwards, it calls kvm_arch_vcpu_destroy(). However, if closing the file descriptor races with KVM_RUN in such away that vcpu->arch.st.preempted == 0, the following call stack leads to a NULL pointer dereference in kvm_dirty_run_push(): mark_page_dirty_in_slot+0x192/0x270 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3171 kvm_steal_time_set_preempted arch/x86/kvm/x86.c:4600 [inline] kvm_arch_vcpu_put+0x34e/0x5b0 arch/x86/kvm/x86.c:4618 vcpu_put+0x1b/0x70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:211 vmx_free_vcpu+0xcb/0x130 arch/x86/kvm/vmx/vmx.c:6985 kvm_arch_vcpu_destroy+0x76/0x290 arch/x86/kvm/x86.c:11219 kvm_vcpu_destroy arch/x86/kvm/../../../virt/kvm/kvm_main.c:441 [inline] The fix is to release the dirty page ring after kvm_arch_vcpu_destroy has run. Reported-by: Qiuhao Li Reported-by: Gaoning Pan Reported-by: Yongkang Jia Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 70e05af5ebea..b22f380e3347 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -434,8 +434,8 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id) static void kvm_vcpu_destroy(struct kvm_vcpu *vcpu) { - kvm_dirty_ring_free(&vcpu->dirty_ring); kvm_arch_vcpu_destroy(vcpu); + kvm_dirty_ring_free(&vcpu->dirty_ring); /* * No need for rcu_read_lock as VCPU_RUN is the only place that changes