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Subject: Re: [PATCH] kvm: Use struct_size() in kmalloc()
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190104162910.GA25118@embeddedor>
 <4c4093b5-814d-3337-bc26-d6a491a7944e@embeddedor.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <dde9554e-4fd0-ba8d-bb3f-047c4bf3c84b@redhat.com>
Date:   Wed, 30 Jan 2019 17:08:41 +0100
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On 29/01/19 18:20, Gustavo A. R. Silva wrote:
> Hi all,
> 
> Friendly ping:
> 
> Who can take this?

I cannot find the original message in my inbox, but I've queued it from
the quote below.

Thanks,

Paolo

> Thanks
> --
> Gustavo
> 
> On 1/4/19 10:29 AM, Gustavo A. R. Silva wrote:
>> One of the more common cases of allocation size calculations is finding
>> the size of a structure that has a zero-sized array at the end, along
>> with memory for some number of elements for that array. For example:
>>
>> struct foo {
>>     int stuff;
>>     void *entry[];
>> };
>>
>> instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
>>
>> Instead of leaving these open-coded and prone to type mistakes, we can
>> now use the new struct_size() helper:
>>
>> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
>>
>> This code was detected with the help of Coccinelle.
>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
>> ---
>>  virt/kvm/kvm_main.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 666d0155662d..635b12fdbab8 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -3709,8 +3709,8 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
>>  	if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
>>  		return -ENOSPC;
>>  
>> -	new_bus = kmalloc(sizeof(*bus) + ((bus->dev_count + 1) *
>> -			  sizeof(struct kvm_io_range)), GFP_KERNEL);
>> +	new_bus = kmalloc(struct_size(bus, range, bus->dev_count + 1),
>> +			  GFP_KERNEL);
>>  	if (!new_bus)
>>  		return -ENOMEM;
>>  
>> @@ -3755,8 +3755,8 @@ void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
>>  	if (i == bus->dev_count)
>>  		return;
>>  
>> -	new_bus = kmalloc(sizeof(*bus) + ((bus->dev_count - 1) *
>> -			  sizeof(struct kvm_io_range)), GFP_KERNEL);
>> +	new_bus = kmalloc(struct_size(bus, range, bus->dev_count - 1),
>> +			  GFP_KERNEL);
>>  	if (!new_bus)  {
>>  		pr_err("kvm: failed to shrink bus, removing it completely\n");
>>  		goto broken;
>>