Re: [PATCH 1/2] KVM: Fix NULL-ptr defer after kvm_create_vm fails

[Christian Borntraeger]

On 04.11.19 07:27, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> 
> Reported by syzkaller:
> 
>     kasan: CONFIG_KASAN_INLINE enabled
>     kasan: GPF could be caused by NULL-ptr deref or user memory access
>     general protection fault: 0000 [#1] PREEMPT SMP KASAN
>     CPU: 0 PID: 14727 Comm: syz-executor.3 Not tainted 5.4.0-rc4+ #0
>     RIP: 0010:kvm_coalesced_mmio_init+0x5d/0x110 arch/x86/kvm/../../../virt/kvm/coalesced_mmio.c:121
>     Call Trace:
>      kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3446 [inline]
>      kvm_dev_ioctl+0x781/0x1490 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3494
>      vfs_ioctl fs/ioctl.c:46 [inline]
>      file_ioctl fs/ioctl.c:509 [inline]
>      do_vfs_ioctl+0x196/0x1150 fs/ioctl.c:696
>      ksys_ioctl+0x62/0x90 fs/ioctl.c:713
>      __do_sys_ioctl fs/ioctl.c:720 [inline]
>      __se_sys_ioctl fs/ioctl.c:718 [inline]
>      __x64_sys_ioctl+0x6e/0xb0 fs/ioctl.c:718
>      do_syscall_64+0xca/0x5d0 arch/x86/entry/common.c:290
>      entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Commit 9121923c457d ("kvm: Allocate memslots and buses before calling kvm_arch_init_vm") 
> moves memslots and buses allocations around, however, if kvm->srcu/irq_srcu fails 
> initialization, NULL will be returned instead of error code, NULL will not be intercepted 
> in kvm_dev_ioctl_create_vm() and be deferenced by kvm_coalesced_mmio_init(), this patch 
> fixes it.
> 
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13509b84e00000
> 
> Reported-by: syzbot+89a8060879fa0bd2db4f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 9121923c457d ("kvm: Allocate memslots and buses before calling kvm_arch_init_vm") 
> Cc: Jim Mattson <jmattson@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>

Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>

> ---
>  virt/kvm/kvm_main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d6f0696..8c272eb 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -675,6 +675,7 @@ static struct kvm *kvm_create_vm(unsigned long type)
>  	INIT_HLIST_HEAD(&kvm->irq_ack_notifier_list);
>  #endif
> 
> +	r = -ENOMEM;
>  	if (init_srcu_struct(&kvm->srcu))
>  		goto out_err_no_srcu;
>  	if (init_srcu_struct(&kvm->irq_srcu))
>