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Subject: Re: [PATCH] kvm: Use struct_size() in kmalloc()
To:     Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190104162910.GA25118@embeddedor>
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
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Message-ID: <4c4093b5-814d-3337-bc26-d6a491a7944e@embeddedor.com>
Date:   Tue, 29 Jan 2019 11:20:29 -0600
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In-Reply-To: <20190104162910.GA25118@embeddedor>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi all,

Friendly ping:

Who can take this?

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;
>