Commit 1f466e1f authored by Christoph Hellwig's avatar Christoph Hellwig Committed by David S. Miller
Browse files

net: cleanly handle kernel vs user buffers for ->msg_control 



The msg_control field in struct msghdr can either contain a user
pointer when used with the recvmsg system call, or a kernel pointer
when used with sendmsg.  To complicate things further kernel_recvmsg
can stuff a kernel pointer in and then use set_fs to make the uaccess
helpers accept it.

Replace it with a union of a kernel pointer msg_control field, and
a user pointer msg_control_user one, and allow kernel_recvmsg operate
on a proper kernel pointer using a bitfield to override the normal
choice of a user pointer for recvmsg.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2618d530

include/linux/socket.h

+11 −1
Original line number Diff line number Diff line
@@ -50,7 +50,17 @@ struct msghdr { 
	void		*msg_name;	/* ptr to socket address structure */

	int		msg_namelen;	/* size of socket address structure */

	struct iov_iter	msg_iter;	/* data */

	void		*msg_control;	/* ancillary data */



	/*

	 * Ancillary data. msg_control_user is the user buffer used for the

	 * recv* side when msg_control_is_user is set, msg_control is the kernel

	 * buffer used for all other cases.

	 */

	union {

		void		*msg_control;

		void __user	*msg_control_user;

	};

	bool		msg_control_is_user : 1;

	__kernel_size_t	msg_controllen;	/* ancillary data buffer length */

	unsigned int	msg_flags;	/* flags on received message */

	struct kiocb	*msg_iocb;	/* ptr to iocb for async requests */

net/compat.c

+3 −2
Original line number Diff line number Diff line
@@ -56,7 +56,8 @@ int __get_compat_msghdr(struct msghdr *kmsg, 
	if (kmsg->msg_namelen > sizeof(struct sockaddr_storage))

		kmsg->msg_namelen = sizeof(struct sockaddr_storage);



	kmsg->msg_control = compat_ptr(msg.msg_control);

	kmsg->msg_control_is_user = true;

	kmsg->msg_control_user = compat_ptr(msg.msg_control);

	kmsg->msg_controllen = msg.msg_controllen;



	if (save_addr)
@@ -121,7 +122,7 @@ int get_compat_msghdr(struct msghdr *kmsg, 
	((ucmlen) >= sizeof(struct compat_cmsghdr) && \

	 (ucmlen) <= (unsigned long) \

	 ((mhdr)->msg_controllen - \

	  ((char *)(ucmsg) - (char *)(mhdr)->msg_control)))

	  ((char __user *)(ucmsg) - (char __user *)(mhdr)->msg_control_user)))



static inline struct compat_cmsghdr __user *cmsg_compat_nxthdr(struct msghdr *msg,

		struct compat_cmsghdr __user *cmsg, int cmsg_len)

net/core/scm.c

+28 −21
Original line number Diff line number Diff line
@@ -212,16 +212,12 @@ EXPORT_SYMBOL(__scm_send); 


int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)

{

	struct cmsghdr __user *cm

		= (__force struct cmsghdr __user *)msg->msg_control;

	struct cmsghdr cmhdr;

	int cmlen = CMSG_LEN(len);

	int err;



	if (MSG_CMSG_COMPAT & msg->msg_flags)

	if (msg->msg_flags & MSG_CMSG_COMPAT)

		return put_cmsg_compat(msg, level, type, len, data);



	if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {

	if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {

		msg->msg_flags |= MSG_CTRUNC;

		return 0; /* XXX: return error? check spec. */

	}
@@ -229,23 +225,30 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data) 
		msg->msg_flags |= MSG_CTRUNC;

		cmlen = msg->msg_controllen;

	}



	if (msg->msg_control_is_user) {

		struct cmsghdr __user *cm = msg->msg_control_user;

		struct cmsghdr cmhdr;



		cmhdr.cmsg_level = level;

		cmhdr.cmsg_type = type;

		cmhdr.cmsg_len = cmlen;

		if (copy_to_user(cm, &cmhdr, sizeof cmhdr) ||

		    copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm)))

			return -EFAULT;

	} else {

		struct cmsghdr *cm = msg->msg_control;



		cm->cmsg_level = level;

		cm->cmsg_type = type;

		cm->cmsg_len = cmlen;

		memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));

	}



	err = -EFAULT;

	if (copy_to_user(cm, &cmhdr, sizeof cmhdr))

		goto out;

	if (copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm)))

		goto out;

	cmlen = CMSG_SPACE(len);

	if (msg->msg_controllen < cmlen)

		cmlen = msg->msg_controllen;

	cmlen = min(CMSG_SPACE(len), msg->msg_controllen);

	msg->msg_control += cmlen;

	msg->msg_controllen -= cmlen;

	err = 0;

out:

	return err;

	return 0;

}

EXPORT_SYMBOL(put_cmsg);
@@ -328,6 +331,10 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm) 
		return;

	}



	/* no use for FD passing from kernel space callers */

	if (WARN_ON_ONCE(!msg->msg_control_is_user))

		return;



	for (i = 0; i < fdmax; i++) {

		err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);

		if (err)

net/ipv4/ip_sockglue.c

+2 −1
Original line number Diff line number Diff line
@@ -1492,7 +1492,8 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname, 
		if (sk->sk_type != SOCK_STREAM)

			return -ENOPROTOOPT;



		msg.msg_control = (__force void *) optval;

		msg.msg_control_is_user = true;

		msg.msg_control_user = optval;

		msg.msg_controllen = len;

		msg.msg_flags = flags;

net/socket.c

+6 −16
Original line number Diff line number Diff line
@@ -924,14 +924,9 @@ EXPORT_SYMBOL(sock_recvmsg); 
int kernel_recvmsg(struct socket *sock, struct msghdr *msg,

		   struct kvec *vec, size_t num, size_t size, int flags)

{

	mm_segment_t oldfs = get_fs();

	int result;



	msg->msg_control_is_user = false;

	iov_iter_kvec(&msg->msg_iter, READ, vec, num, size);

	set_fs(KERNEL_DS);

	result = sock_recvmsg(sock, msg, flags);

	set_fs(oldfs);

	return result;

	return sock_recvmsg(sock, msg, flags);

}

EXPORT_SYMBOL(kernel_recvmsg);
@@ -2239,7 +2234,8 @@ int __copy_msghdr_from_user(struct msghdr *kmsg, 
	if (copy_from_user(&msg, umsg, sizeof(*umsg)))

		return -EFAULT;



	kmsg->msg_control = (void __force *)msg.msg_control;

	kmsg->msg_control_is_user = true;

	kmsg->msg_control_user = msg.msg_control;

	kmsg->msg_controllen = msg.msg_controllen;

	kmsg->msg_flags = msg.msg_flags;
@@ -2331,16 +2327,10 @@ static int ____sys_sendmsg(struct socket *sock, struct msghdr *msg_sys, 
				goto out;

		}

		err = -EFAULT;

		/*

		 * Careful! Before this, msg_sys->msg_control contains a user pointer.

		 * Afterwards, it will be a kernel pointer. Thus the compiler-assisted

		 * checking falls down on this.

		 */

		if (copy_from_user(ctl_buf,

				   (void __user __force *)msg_sys->msg_control,

				   ctl_len))

		if (copy_from_user(ctl_buf, msg_sys->msg_control_user, ctl_len))

			goto out_freectl;

		msg_sys->msg_control = ctl_buf;

		msg_sys->msg_control_is_user = false;

	}

	msg_sys->msg_flags = flags;

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