[PATCH net] rxrpc: Work around usercopy check

[David Miller]

From: David Howells <dhowells at redhat.com>
Date: Thu, 15 Feb 2018 22:59:00 +0000

> Due to a check recently added to copy_to_user(), it's now not permitted to
> copy from slab-held data to userspace unless the slab is whitelisted.  This
> affects rxrpc_recvmsg() when it attempts to place an RXRPC_USER_CALL_ID
> control message in the userspace control message buffer.  A warning is
> generated by usercopy_warn() because the source is the copy of the
> user_call_ID retained in the rxrpc_call struct.
> 
> Work around the issue by copying the user_call_ID to a variable on the
> stack and passing that to put_cmsg().
> 
> The warning generated looks like:
 ...
> Reported-by: Jonathan Billings <jsbillings at jsbillings.org>
> Signed-off-by: David Howells <dhowells at redhat.com>
> Acked-by: Kees Cook <keescook at chromium.org>
> Tested-by: Jonathan Billings <jsbillings at jsbillings.org>

Applied, thanks David.