H. Peter Anvin <hpa@xxxxxxxxx> 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? Fair enough. This happens e.g. when trying to add xfrm policies or SAs from 32bit x86 userspace on x86_64 kernels, e.g. commands like "ip xfrm pol add dir in" fail due to user/kernelspace structure size mismatch. One structure that has this problem is struct xfrm_userpolicy_info, but there are more. Now, I realize that adding a write compat syscall is borderline insanity, and I am open to suggestions. In fact, I would even accept a "userspace must use sendmsg() when dealing with xfrm netlink"; the only problem is that my pending xfrm compat patches depend on this patch being accepted [ or, rather, they depend on the MSG_COMPAT flag being set; which is currently only done when userspace uses sendmsg(). In fact, "ip xfrm .. " even works with the xfrm compat patch set applied because ip xfrm ... happens to use sendmsg(). But not all userspace apps do this ]. Thanks, Florian -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
