Re: io_uring, IORING_OP_RECVMSG and ancillary data

[Jens Axboe <axboe@kernel.dk>]

On 4/27/20 1:29 PM, Jens Axboe wrote:
> On 4/27/20 1:20 PM, Jann Horn wrote:
>> On Sat, Apr 25, 2020 at 10:23 PM Jens Axboe <axboe@kernel.dk> wrote:
>>> On 4/25/20 11:29 AM, Andreas Smas wrote:
>>>> Hi,
>>>>
>>>> Tried to use io_uring with OP_RECVMSG with ancillary buffers (for my
>>>> particular use case I'm using SO_TIMESTAMP for incoming UDP packets).
>>>>
>>>> These submissions fail with EINVAL due to the check in __sys_recvmsg_sock().
>>>>
>>>> The following hack fixes the problem for me and I get valid timestamps
>>>> back. Not suggesting this is the real fix as I'm not sure what the
>>>> implications of this is.
>>>>
>>>> Any insight into this would be much appreciated.
>>>
>>> It was originally disabled because of a security issue, but I do think
>>> it's safe to enable again.
>>>
>>> Adding the io-uring list and Jann as well, leaving patch intact below.
>>>
>>>> diff --git a/net/socket.c b/net/socket.c
>>>> index 2dd739fba866..689f41f4156e 100644
>>>> --- a/net/socket.c
>>>> +++ b/net/socket.c
>>>> @@ -2637,10 +2637,6 @@ long __sys_recvmsg_sock(struct socket *sock,
>>>> struct msghdr *msg,
>>>>                         struct user_msghdr __user *umsg,
>>>>                         struct sockaddr __user *uaddr, unsigned int flags)
>>>>  {
>>>> -       /* disallow ancillary data requests from this path */
>>>> -       if (msg->msg_control || msg->msg_controllen)
>>>> -               return -EINVAL;
>>>> -
>>>>         return ____sys_recvmsg(sock, msg, umsg, uaddr, flags, 0);
>>>>  }
>>
>> I think that's hard to get right. In particular, unix domain sockets
>> can currently pass file descriptors in control data - so you'd need to
>> set the file_table flag for recvmsg and sendmsg. And I'm not sure
>> whether, to make this robust, there should be a whitelist of types of
>> control messages that are permitted to be used with io_uring, or
>> something like that...
>>
>> I think of ancillary buffers as being kind of like ioctl handlers in
>> this regard.
> 
> Good point. I'll send out something that hopefully will be enough to
> be useful, whole not allowing anything randomly.

That things is a bit of a mess... How about something like this for
starters?


diff --git a/fs/io_uring.c b/fs/io_uring.c
index 084dfade5cda..40aa5b38367e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3570,6 +3570,37 @@ static int io_sendmsg_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return ret;
 }
 
+static bool __io_net_allow_cmsg(struct cmsghdr *cmsg)
+{
+	switch (cmsg->cmsg_level) {
+	case SOL_SOCKET:
+		if (cmsg->cmsg_type != SCM_RIGHTS &&
+		    cmsg->cmsg_type != SCM_CREDENTIALS)
+			return true;
+		return false;
+	case SOL_IP:
+	case SOL_TCP:
+	case SOL_IPV6:
+	case SOL_ICMPV6:
+	case SOL_SCTP:
+		return true;
+	default:
+		return false;
+	}
+}
+
+static bool io_net_allow_cmsg(struct msghdr *msg)
+{
+	struct cmsghdr *cmsg;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (!__io_net_allow_cmsg(cmsg))
+			return false;
+	}
+
+	return true;
+}
+
 static int io_sendmsg(struct io_kiocb *req, bool force_nonblock)
 {
 	struct io_async_msghdr *kmsg = NULL;
@@ -3604,6 +3635,11 @@ static int io_sendmsg(struct io_kiocb *req, bool force_nonblock)
 				return ret;
 		}
 
+		if (!io_net_allow_cmsg(&kmsg->msg)) {
+			ret = -EINVAL;
+			goto err;
+		}
+
 		flags = req->sr_msg.msg_flags;
 		if (flags & MSG_DONTWAIT)
 			req->flags |= REQ_F_NOWAIT;
@@ -3617,6 +3653,7 @@ static int io_sendmsg(struct io_kiocb *req, bool force_nonblock)
 			ret = -EINTR;
 	}
 
+err:
 	if (kmsg && kmsg->iov != kmsg->fast_iov)
 		kfree(kmsg->iov);
 	req->flags &= ~REQ_F_NEED_CLEANUP;
@@ -3840,6 +3877,11 @@ static int io_recvmsg(struct io_kiocb *req, bool force_nonblock)
 				return ret;
 		}
 
+		if (!io_net_allow_cmsg(&kmsg->msg)) {
+			ret = -EINVAL;
+			goto err;
+		}
+
 		kbuf = io_recv_buffer_select(req, &cflags, !force_nonblock);
 		if (IS_ERR(kbuf)) {
 			return PTR_ERR(kbuf);
@@ -3863,6 +3905,7 @@ static int io_recvmsg(struct io_kiocb *req, bool force_nonblock)
 			ret = -EINTR;
 	}
 
+err:
 	if (kmsg && kmsg->iov != kmsg->fast_iov)
 		kfree(kmsg->iov);
 	req->flags &= ~REQ_F_NEED_CLEANUP;
diff --git a/net/socket.c b/net/socket.c
index 2dd739fba866..78cdf9a8cf73 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2425,10 +2425,6 @@ static int ___sys_sendmsg(struct socket *sock, struct user_msghdr __user *msg,
 long __sys_sendmsg_sock(struct socket *sock, struct msghdr *msg,
 			unsigned int flags)
 {
-	/* disallow ancillary data requests from this path */
-	if (msg->msg_control || msg->msg_controllen)
-		return -EINVAL;
-
 	return ____sys_sendmsg(sock, msg, flags, NULL, 0);
 }
 
@@ -2637,10 +2633,6 @@ long __sys_recvmsg_sock(struct socket *sock, struct msghdr *msg,
 			struct user_msghdr __user *umsg,
 			struct sockaddr __user *uaddr, unsigned int flags)
 {
-	/* disallow ancillary data requests from this path */
-	if (msg->msg_control || msg->msg_controllen)
-		return -EINVAL;
-
 	return ____sys_recvmsg(sock, msg, umsg, uaddr, flags, 0);
 }

-- 
Jens Axboe