Re: [PATCH -next] x86, fs: add sys_compat_write for net/socket.c

On 03/30/2010 10:51 AM, Florian Westphal wrote:

On some configurations, e.g. x86_64 with 32bit userspace, netlink/xfrm
misinterprets messages from userspace due to different structure
layout (u64 has different alignment requirements on x86 vs. x86_64).

As long as messages are sent via sendmsg(), this could be handled via
net/compat.c; it will set the CMSG_MSG_COMPAT flag in struct msghdr
for compat tasks, which would allow to the xfrm_user code to detect
when messages need compat fixups.

Unfortunately, some programs (e.g. pluto ike daemon), send netlink data
to the kernel using write().

Thus, introduce f_ops->compat_aio_write and compat_sys_write to treat
writes on sockets specially.

This only wires up compat_sys_write for x86/x86_64 -- at the moment this
is only required to parse xfrm netlink messages, which happen to only
need special treatment in case of COMPAT_FOR_U64_ALIGNMENT=y.

Setting CMSG_MSG_COMPAT depending on plain is_compat_task() in net/socket.c
was not done due to concerns regarding the kernel doing socket
writes in response to a user event (which might set MSG_COMPAT erronously).

OK... I have to ask the question:

This only applies if you're using unpacked structures with
non-naturally-aligned objects in them.  Where to we have those, and can
we shoot the authors?

	-hpa