Subject: [PATCH 2/2] net: disallow ancillary data for __sys_{send,recv}msg_file()

From: Jens Axboe <[email-masked]>
Date: Mon, 25 Nov 2019 18:31:45 -0700

Only io_uring uses (and added) these, and we want to disallow the
use of sendmsg/recvmsg for anything but regular data transfers.
Use the newly added prep helper to split the msghdr copy out from
the core function, to check for msg_control and msg_controllen
settings. If either is set, we return -EINVAL.

Signed-off-by: Jens Axboe <[email-masked]>
---
 net/socket.c | 43 +++++++++++++++++++++++++++++++++++++------
 1 file changed, 37 insertions(+), 6 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index da729df8f03d..2d6083b881ab 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2388,12 +2388,27 @@ static int ___sys_sendmsg(struct socket *sock, struct user_msghdr __user *msg,
 /*
  *	BSD sendmsg interface
  */
-long __sys_sendmsg_sock(struct socket *sock, struct user_msghdr __user *msg,
+long __sys_sendmsg_sock(struct socket *sock, struct user_msghdr __user *umsg,
 			unsigned int flags)
 {
-	struct msghdr msg_sys;
+	struct iovec iovstack[UIO_FASTIOV], *iov = iovstack;
+	struct sockaddr_storage address;
+	struct msghdr msg = { .msg_name = &address };
+	ssize_t err;
+
+	err = sendmsg_copy_msghdr(&msg, umsg, flags, &iov);
+	if (err)
+		return err;
+	/* disallow ancillary data requests from this path */
+	if (msg.msg_control || msg.msg_controllen) {
+		err = -EINVAL;
+		goto out;
+	}
 
-	return ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL, 0);
+	err = ____sys_sendmsg(sock, &msg, flags, NULL, 0);
+out:
+	kfree(iov);
+	return err;
 }
 
 long __sys_sendmsg(int fd, struct user_msghdr __user *msg, unsigned int flags,
@@ -2592,12 +2607,28 @@ static int ___sys_recvmsg(struct socket *sock, struct user_msghdr __user *msg,
  *	BSD recvmsg interface
  */
 
-long __sys_recvmsg_sock(struct socket *sock, struct user_msghdr __user *msg,
+long __sys_recvmsg_sock(struct socket *sock, struct user_msghdr __user *umsg,
 			unsigned int flags)
 {
-	struct msghdr msg_sys;
+	struct iovec iovstack[UIO_FASTIOV], *iov = iovstack;
+	struct sockaddr_storage address;
+	struct msghdr msg = { .msg_name = &address };
+	struct sockaddr __user *uaddr;
+	ssize_t err;
 
-	return ___sys_recvmsg(sock, msg, &msg_sys, flags, 0);
+	err = recvmsg_copy_msghdr(&msg, umsg, flags, &uaddr, &iov);
+	if (err)
+		return err;
+	/* disallow ancillary data requests from this path */
+	if (msg.msg_control || msg.msg_controllen) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = ____sys_recvmsg(sock, &msg, umsg, uaddr, flags, 0);
+out:
+	kfree(iov);
+	return err;
 }
 
 long __sys_recvmsg(int fd, struct user_msghdr __user *msg, unsigned int flags,
-- 
2.24.0