[PATCH -next] KVM: arm64: Fix possible null-ptr-deref in idregs_debug_show

[cuigaosheng]

On 2024/10/24 17:29, Marc Zyngier wrote:
> On Thu, 24 Oct 2024 09:33:50 +0100,
> Gaosheng Cui <cuigaosheng1 at huawei.com> wrote:
>> The idregs_debug_show() maybe return nullptr, we need to check desc
>> before dereference it to avoid possible null pointer dereferences.
>>
>> Fixes: 410db103f6eb ("KVM: arm64: Make idregs debugfs iterator search sysreg table directly")
>> Signed-off-by: Gaosheng Cui <cuigaosheng1 at huawei.com>
>> ---
>>   arch/arm64/kvm/sys_regs.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index ff8c4e1b847e..b1c59773b9c0 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -4135,7 +4135,7 @@ static int idregs_debug_show(struct seq_file *s, void *v)
>>   
>>   	desc = idregs_debug_find(kvm, kvm->arch.idreg_debugfs_iter);
>>   
>> -	if (!desc->name)
>> +	if (!desc || !desc->name)
>>   		return 0;
>>   
>>   	seq_printf(s, "%20s:\t%016llx\n",
> Can you show a case where this happens in practice?
>
> The check for NULL is already in idregs_debug_next(), and I don't see
> how this can actually be triggered.

I haven't found a scenario that can trigger this problem，this patch was
discovered during code review，I will try to prove it.

Thanks for your work.

>
> Thanks,
>
> 	M.
>