[PATCH] KVM: Add the check and free to avoid unknown errors.

[PATCH] KVM: Add the check and free to avoid unknown errors.

[Haiwei Li]

From: Haiwei Li <lihaiwei@tencent.com>

If 'kvm_create_vm_debugfs()' fails in 'kzalloc(sizeof(*stat_data), ...)',
'kvm_destroy_vm_debugfs()' will be called by the final fput(file) in
'kvm_dev_ioctl_create_vm()'.

Add the check and free to avoid unknown errors.

Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
---
  virt/kvm/kvm_main.c | 5 ++++-
  1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 67ae2d5..18a32e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -617,8 +617,11 @@ static void kvm_destroy_vm_debugfs(struct kvm *kvm)
  	debugfs_remove_recursive(kvm->debugfs_dentry);

  	if (kvm->debugfs_stat_data) {
-		for (i = 0; i < kvm_debugfs_num_entries; i++)
+		for (i = 0; i < kvm_debugfs_num_entries; i++) {
+			if (!kvm->debugfs_stat_data[i])
+				break;
  			kfree(kvm->debugfs_stat_data[i]);
+		}
  		kfree(kvm->debugfs_stat_data);
  	}
  }
--
1.8.3.1

Re: [PATCH] KVM: Add the check and free to avoid unknown errors.

[Paolo Bonzini]

On 14/02/20 22:02, Haiwei Li wrote:
> From: Haiwei Li <lihaiwei@tencent.com>
> 
> If 'kvm_create_vm_debugfs()' fails in 'kzalloc(sizeof(*stat_data), ...)',
> 'kvm_destroy_vm_debugfs()' will be called by the final fput(file) in
> 'kvm_dev_ioctl_create_vm()'.

Can you explain better?  It is okay to pass NULL to kfree.

Paolo

> Add the check and free to avoid unknown errors.
> 
> Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
> ---
>  virt/kvm/kvm_main.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67ae2d5..18a32e1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -617,8 +617,11 @@ static void kvm_destroy_vm_debugfs(struct kvm *kvm)
>      debugfs_remove_recursive(kvm->debugfs_dentry);
> 
>      if (kvm->debugfs_stat_data) {
> -        for (i = 0; i < kvm_debugfs_num_entries; i++)
> +        for (i = 0; i < kvm_debugfs_num_entries; i++) {
> +            if (!kvm->debugfs_stat_data[i])
> +                break;
>              kfree(kvm->debugfs_stat_data[i]);
> +        }
>          kfree(kvm->debugfs_stat_data);
>      }
>  }
> -- 
> 1.8.3.1
> 

Re: [PATCH] KVM: Add the check and free to avoid unknown errors.

[linmiaohe]

Hi:
Haiwei Li <lihaiwei.kernel@gmail.com> wrote:
> From: Haiwei Li <lihaiwei@tencent.com>
>
> If 'kvm_create_vm_debugfs()' fails in 'kzalloc(sizeof(*stat_data), ...)', 'kvm_destroy_vm_debugfs()' will be called by the final fput(file) in 'kvm_dev_ioctl_create_vm()'.
>
> Add the check and free to avoid unknown errors.

Add the check and free? According to the code,it seem what you mean is "add the check against free" ?
 
>
> Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
>
>   	if (kvm->debugfs_stat_data) {
> -		for (i = 0; i < kvm_debugfs_num_entries; i++)
> +		for (i = 0; i < kvm_debugfs_num_entries; i++) {
> +			if (!kvm->debugfs_stat_data[i])
> +				break;
>   			kfree(kvm->debugfs_stat_data[i]);
> +		}
>   		kfree(kvm->debugfs_stat_data);
>   	}
>   }

If (!kvm->debugfs_stat_data[i]) is checked in kfree() internal. And break early seems have no different effect.
Could you please explain what unknown errors may occur? And how? Thanks.

Re: [PATCH] KVM: Add the check and free to avoid unknown errors.

[Haiwei Li]

linmiaohe <linmiaohe@huawei.com> 于2020年2月15日周六 上午10:00写道：
>
> Hi:
> Haiwei Li <lihaiwei.kernel@gmail.com> wrote:
> > From: Haiwei Li <lihaiwei@tencent.com>
> >
> > If 'kvm_create_vm_debugfs()' fails in 'kzalloc(sizeof(*stat_data), ...)', 'kvm_destroy_vm_debugfs()' will be called by the final fput(file) in 'kvm_dev_ioctl_create_vm()'.
> >
> > Add the check and free to avoid unknown errors.
>
> Add the check and free? According to the code,it seem what you mean is "add the check against free" ?

Right, i can change the description.

>
> >
> > Signed-off-by: Haiwei Li <lihaiwei@tencent.com>
> >
> >       if (kvm->debugfs_stat_data) {
> > -             for (i = 0; i < kvm_debugfs_num_entries; i++)
> > +             for (i = 0; i < kvm_debugfs_num_entries; i++) {
> > +                     if (!kvm->debugfs_stat_data[i])
> > +                             break;
> >                       kfree(kvm->debugfs_stat_data[i]);
> > +             }
> >               kfree(kvm->debugfs_stat_data);
> >       }
> >   }
>
> If (!kvm->debugfs_stat_data[i]) is checked in kfree() internal. And break early seems have no different effect.
> Could you please explain what unknown errors may occur? And how? Thanks.

I get the free() code. It is just like what you said. Thanks a lot.
Break early is useful. If kvm->debugfs_stat_data[i] is null, breaking
early can reduce the check.

>