Re: [PATCH 7/9] Simplify bound checks in capabilities for copy_from_user

[James Morris]

On Tue, 29 Sep 2009, Arjan van de Ven wrote:

> From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> Subject: [PATCH 7/9] Simplify bound checks in capabilities for copy_from_user
> CC: James Morris <jmorris@xxxxxxxxx>
> 
> The capabilities syscall has a copy_from_user() call where gcc currently
> cannot prove to itself that the copy is always within bounds.
> 
> This patch adds a very explicity bound check to prove to gcc that 
> this copy_from_user cannot overflow its destination buffer.
> 
> Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>

Acked-by: James Morris <jmorris@xxxxxxxxx>


> diff --git a/kernel/capability.c b/kernel/capability.c
> index 4e17041..204f11f 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -238,7 +241,7 @@ SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
>  SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
>  {
>  	struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
> -	unsigned i, tocopy;
> +	unsigned i, tocopy, copybytes;
>  	kernel_cap_t inheritable, permitted, effective;
>  	struct cred *new;
>  	int ret;
> @@ -255,8 +258,11 @@ SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
>  	if (pid != 0 && pid != task_pid_vnr(current))
>  		return -EPERM;
>  
> -	if (copy_from_user(&kdata, data,
> -			   tocopy * sizeof(struct __user_cap_data_struct)))
> +	copybytes = tocopy * sizeof(struct __user_cap_data_struct);
> +	if (copybytes > sizeof(kdata))
> +		return -EFAULT;
> +
> +	if (copy_from_user(&kdata, data, copybytes))
>  		return -EFAULT;
>  
>  	for (i = 0; i < tocopy; i++) {
> 
> 
> 
> -- 
> Arjan van de Ven 	Intel Open Source Technology Centre
> For development, discussion and tips for power savings, 
> visit http://www.lesswatts.org
> 

-- 
James Morris
<jmorris@xxxxxxxxx>
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