Em 22 de julho de 2015 10:13:22 BRT, David Laight <David.Laight@xxxxxxxxxx> escreveu:
>From: Marcelo Ricardo Leitner
>> Sent: 14 July 2015 18:13
>> SCTP has this operation to peel off associations from a given socket
>and
>> create a new socket using this association. We currently have two
>ways
>> to use this operation:
>> - via getsockopt(), on which it will also create and return a file
>> descriptor for this new socket
>> - via sctp_do_peeloff(), which is for kernel only
>>
>> The caveat with using sctp_do_peeloff() directly is that it creates a
>> dependency to SCTP module, while all other operations are handled via
>> kernel_{socket,sendmsg,getsockopt...}() interface. This causes the
>> kernel to load SCTP module even when it's not really used.
>>
>> This patch then creates a new sockopt that is to be used only by
>kernel
>> users of this protocol. This new sockopt will not allocate a file
>> descriptor but instead just return the socket pointer directly.
>>
>> Kernel users are actually identified by if the parent socket has or
>not
>> a fd attached to it. If not, it's a kernel a user.
>>
>> If called by an user application, it will just return -EPERM.
>>
>> Even though it's not intended for user applications, it's listed
>under
>> uapi header. That's because hidding this wouldn't add any extra
>security
>> and to keep the sockopt list in one place, so it's easy to check
>> available numbers to use.
>>
>> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
>...
>> +static int sctp_getsockopt_peeloff_kernel(struct sock *sk, int len,
>> + char __user *optval, int __user *optlen)
>> +{
>> + sctp_peeloff_kernel_arg_t peeloff;
>> + struct socket *newsock;
>> + int retval = 0;
>> +
>> + /* We only allow this operation if parent socket also hadn't a
>> + * file descriptor allocated to it, mainly as a way to make sure
>> + * that this is really a kernel socket.
>> + */
>> + if (sk->sk_socket->file)
>> + return -EPERM;
>> +
>> + if (len < sizeof(sctp_peeloff_kernel_arg_t))
>> + return -EINVAL;
>> + len = sizeof(sctp_peeloff_kernel_arg_t);
>> + if (copy_from_user(&peeloff, optval, len))
>> + return -EFAULT;
>
>You can't need copy_from_user() here, the buffer would surely be
>kernel.
>
> David
Yes. It was just to avoid errors from static checkers, if any. Same for the __user in function prototype.
--
Sent from mobile. Please excuse my brevity.
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