Re: [PATCH] kvm: properly check debugfs dentry before using it

[Paolo Bonzini]

On 28/02/19 16:08, Greg Kroah-Hartman wrote:
> debugfs can now report an error code if something went wrong instead of
> just NULL.  So if the return value is to be used as a "real" dentry, it
> needs to be checked if it is an error before dereferencing it.
> 
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL").  syzbot has found a way to trigger multiple debugfs
> files attempting to be created, which fails, and then the error code
> gets passed to dentry_path_raw() which obviously does not like it.
> 
> Reported-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: "Radim KrÄmÃÅ" <rkrcmar@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> ---
> 
> Paolo, this should be merged into 5.0-final, and if not there, then
> 5.1-rc1 and then backported to 5.0 through the stable tree.  If you
> want me to send this to Linus, I will be glad to do so.
> 
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 585845203db8..076bc38963bf 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
>  	}
>  	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
>  
> -	if (kvm->debugfs_dentry) {
> +	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
>  		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
>  
>  		if (p) {
> 

Sure, go ahead.

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

Paolo