xref: /illumos-gate/usr/src/uts/common/io/ptm.c (revision 1fa2a664)

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
 */
/*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/
/*	  All Rights Reserved	*/

/*
 * Copyright 2020 OmniOS Community Edition (OmniOSce) Association.
 * Copyright 2021 Oxide Computer Company
 */

/*
 * PSEUDO-TERMINAL MANAGER DRIVER (PTM)
 *
 * The pseudo-terminal subsystem simulates a terminal connection, where the
 * manager side represents the terminal and the subsidiary represents the user
 * process's special device end point.  The manager device is set up as a
 * cloned device where its major device number is the major for the clone
 * device and its minor device number is the major for the ptm driver.  There
 * are no nodes in the file system for manager devices.  The manager pseudo
 * driver is opened using the open(2) system call with /dev/ptmx as the device
 * parameter.  The clone open finds the next available minor device for the ptm
 * major device.
 *
 * A manager device is available only if it and its corresponding subsidiary
 * device are not already open.  When the manager device is opened, the
 * corresponding subsidiary device is automatically locked out.  Only one open
 * is allowed on a manager device.  Multiple opens are allowed on the
 * subsidiary device.  After both the manager and subsidiary have been opened,
 * the user has two file descriptors which are the end points of a full duplex
 * connection composed of two streams which are automatically connected at the
 * manager and subsidiary drivers.  The user may then push modules onto either
 * side of the stream pair.
 *
 * The manager and subsidiary drivers pass all messages to their adjacent
 * queues.  Only the M_FLUSH needs some processing.  Because the read queue of
 * one side is connected to the write queue of the other, the FLUSHR flag is
 * changed to the FLUSHW flag and vice versa.  When the manager device is
 * closed an M_HANGUP message is sent to the subsidiary device which will
 * render the device unusable.  The process on the subsidiary side gets an EIO
 * error when attempting to write on that stream but it will be able to read
 * any data remaining on the stream head read queue.  When all the data has
 * been read, read() returns 0 indicating that the stream can no longer be
 * used.  On the last close of the subsidiary device, a 0-length message is
 * sent to the manager device.  When the application on the manager side issues
 * a read() or getmsg() and 0 is returned, the user of the manager device
 * decides whether to issue a close() that dismantles the pseudo-terminal
 * subsystem.  If the manager device is not closed, the pseudo-terminal
 * subsystem will be available to another user to open the subsidiary device.
 *
 * If O_NONBLOCK or O_NDELAY is set, read on the manager side returns -1 with
 * errno set to EAGAIN if no data is available, and write returns -1 with errno
 * set to EAGAIN if there is internal flow control.
 *
 *
 * IOCTLS
 *
 *	ISPTM
 *		Determines whether the file descriptor is that of an open
 *		manager device.  Return code of zero indicates that the file
 *		descriptor represents a manager device.
 *
 *	UNLKPT
 *		Unlocks the manager and subsidiary devices.  It returns 0 on
 *		success. On failure, the errno is set to EINVAL indicating that
 *		the manager device is not open.
 *
 *	ZONEPT
 *		Sets the zone membership of the associated subsidiary device.
 *
 *	GRPPT
 *		Sets the group owner of the associated subsidiary device.
 *
 *
 * SYNCHRONIZATION
 *
 * All global data synchronization between ptm/pts is done via global ptms_lock
 * mutex which is initialized at system boot time from ptms_initspace (called
 * from space.c).
 *
 * Individual fields of pt_ttys structure (except ptm_rdq, pts_rdq and
 * pt_nullmsg) are protected by pt_ttys.pt_lock mutex.
 *
 * PT_ENTER_READ/PT_ENTER_WRITE are reference counter based read-write locks
 * which allow reader locks to be reacquired by the same thread (usual
 * reader/writer locks can't be used for that purpose since it is illegal for a
 * thread to acquire a lock it already holds, even as a reader). The sole
 * purpose of these macros is to guarantee that the peer queue will not
 * disappear (due to closing peer) while it is used. It is safe to use
 * PT_ENTER_READ/PT_EXIT_READ brackets across calls like putq/putnext (since
 * they are not real locks but reference counts).
 *
 * PT_ENTER_WRITE/PT_EXIT_WRITE brackets are used ONLY in manager/subsidiary
 * open/close paths to modify ptm_rdq and pts_rdq fields. These fields should
 * be set to appropriate queues *after* qprocson() is called during open (to
 * prevent peer from accessing the queue with incomplete plumbing) and set to
 * NULL before qprocsoff() is called during close.
 *
 * The pt_nullmsg field is only used in open/close routines and it is also
 * protected by PT_ENTER_WRITE/PT_EXIT_WRITE brackets to avoid extra mutex
 * holds.
 *
 *
 * LOCK ORDERING
 *
 * If both ptms_lock and per-pty lock should be held, ptms_lock should always
 * be entered first, followed by per-pty lock.
 *
 * See ptms.h, pts.c, and ptms_conf.c for more information.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/file.h>
#include <sys/sysmacros.h>
#include <sys/stream.h>
#include <sys/stropts.h>
#include <sys/proc.h>
#include <sys/errno.h>
#include <sys/debug.h>
#include <sys/cmn_err.h>
#include <sys/ptms.h>
#include <sys/stat.h>
#include <sys/strsun.h>
#include <sys/systm.h>
#include <sys/modctl.h>
#include <sys/conf.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/zone.h>

#ifdef DEBUG
int ptm_debug = 0;
#define	DBG(a)	 if (ptm_debug) cmn_err(CE_NOTE, a)
#else
#define	DBG(a)
#endif

static int ptmopen(queue_t *, dev_t *, int, int, cred_t *);
static int ptmclose(queue_t *, int, cred_t *);
static int ptmwput(queue_t *, mblk_t *);
static int ptmrsrv(queue_t *);
static int ptmwsrv(queue_t *);

static struct module_info ptm_info = {
	0xdead,
	"ptm",
	0,
	512,
	512,
	128
};

static struct qinit ptmrint = {
	NULL,
	ptmrsrv,
	ptmopen,
	ptmclose,
	NULL,
	&ptm_info,
	NULL
};

static struct qinit ptmwint = {
	ptmwput,
	ptmwsrv,
	NULL,
	NULL,
	NULL,
	&ptm_info,
	NULL
};

static struct streamtab ptminfo = {
	&ptmrint,
	&ptmwint,
	NULL,
	NULL
};

static int ptm_attach(dev_info_t *, ddi_attach_cmd_t);
static int ptm_detach(dev_info_t *, ddi_detach_cmd_t);
static int ptm_devinfo(dev_info_t *, ddi_info_cmd_t, void *, void **);

static dev_info_t	*ptm_dip;		/* private devinfo pointer */

/*
 * this will define (struct cb_ops cb_ptm_ops) and (struct dev_ops ptm_ops)
 */
DDI_DEFINE_STREAM_OPS(ptm_ops, nulldev, nulldev, ptm_attach, ptm_detach,
    nodev, ptm_devinfo, D_MP, &ptminfo, ddi_quiesce_not_supported);

/*
 * Module linkage information for the kernel.
 */

static struct modldrv modldrv = {
	&mod_driverops,
	"Pseudo-Terminal Manager Driver",
	&ptm_ops,
};

static struct modlinkage modlinkage = {
	MODREV_1,
	&modldrv,
	NULL
};

int
_init(void)
{
	int rc;

	if ((rc = mod_install(&modlinkage)) == 0)
		ptms_init();
	return (rc);
}

int
_fini(void)
{
	return (mod_remove(&modlinkage));
}

int
_info(struct modinfo *modinfop)
{
	return (mod_info(&modlinkage, modinfop));
}

static int
ptm_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
	if (cmd != DDI_ATTACH)
		return (DDI_FAILURE);

	if (ddi_create_minor_node(devi, "ptmajor", S_IFCHR,
	    0, DDI_PSEUDO, 0) == DDI_FAILURE) {
		ddi_remove_minor_node(devi, NULL);
		return (DDI_FAILURE);
	}
	if (ddi_create_minor_node(devi, "ptmx", S_IFCHR,
	    0, DDI_PSEUDO, CLONE_DEV) == DDI_FAILURE) {
		ddi_remove_minor_node(devi, NULL);
		return (DDI_FAILURE);
	}
	ptm_dip = devi;

	return (DDI_SUCCESS);
}

static int
ptm_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
{
	if (cmd != DDI_DETACH)
		return (DDI_FAILURE);

	ddi_remove_minor_node(devi, NULL);
	return (DDI_SUCCESS);
}

static int
ptm_devinfo(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg,
    void **result)
{
	int error;

	switch (infocmd) {
	case DDI_INFO_DEVT2DEVINFO:
		if (ptm_dip == NULL) {
			error = DDI_FAILURE;
		} else {
			*result = (void *)ptm_dip;
			error = DDI_SUCCESS;
		}
		break;
	case DDI_INFO_DEVT2INSTANCE:
		*result = (void *)0;
		error = DDI_SUCCESS;
		break;
	default:
		error = DDI_FAILURE;
	}
	return (error);
}


/*
 * Open a minor of the manager device. Store the write queue pointer and set
 * the pt_state field to (PTMOPEN | PTLOCK).
 * This code will work properly with both clone opens and direct opens of the
 * manager device.
 */
static int
ptmopen(
	queue_t *rqp,		/* pointer to the read side queue */
	dev_t   *devp,		/* pointer to stream tail's dev */
	int	oflag,		/* the user open(2) supplied flags */
	int	sflag,		/* open state flag */
	cred_t  *credp)		/* credentials */
{
	struct pt_ttys	*ptmp;
	mblk_t		*mop;		/* ptr to a setopts message block */
	struct stroptions *sop;
	minor_t		dminor = getminor(*devp);

	/* Allow reopen */
	if (rqp->q_ptr != NULL)
		return (0);

	if (sflag & MODOPEN)
		return (ENXIO);

	if (!(sflag & CLONEOPEN) && dminor != 0) {
		/*
		 * This is a direct open to specific manager device through an
		 * artificially created entry with specific minor in
		 * /dev/directory.  Such behavior is not supported.
		 */
		return (ENXIO);
	}

	/*
	 * The manager open requires that the subsidiary be attached before it
	 * returns so that attempts to open the subsidiary will succeeed
	 */
	if (ptms_attach_subsidiary() != 0) {
		return (ENXIO);
	}

	mop = allocb(sizeof (struct stroptions), BPRI_MED);
	if (mop == NULL) {
		DDBG("ptmopen(): mop allocation failed\n", 0);
		return (ENOMEM);
	}

	if ((ptmp = pt_ttys_alloc()) == NULL) {
		DDBG("ptmopen(): pty allocation failed\n", 0);
		freemsg(mop);
		return (ENOMEM);
	}

	dminor = ptmp->pt_minor;

	DDBGP("ptmopen(): allocated ptmp %p\n", (uintptr_t)ptmp);
	DDBG("ptmopen(): allocated minor %d\n", dminor);

	WR(rqp)->q_ptr = rqp->q_ptr = ptmp;

	qprocson(rqp);

	/* Allow subsidiary to send messages to manager */
	PT_ENTER_WRITE(ptmp);
	ptmp->ptm_rdq = rqp;
	PT_EXIT_WRITE(ptmp);

	/*
	 * set up hi/lo water marks on stream head read queue
	 * and add controlling tty if not set
	 */
	mop->b_datap->db_type = M_SETOPTS;
	mop->b_wptr += sizeof (struct stroptions);
	sop = (struct stroptions *)mop->b_rptr;
	if (oflag & FNOCTTY)
		sop->so_flags = SO_HIWAT | SO_LOWAT;
	else
		sop->so_flags = SO_HIWAT | SO_LOWAT | SO_ISTTY;
	sop->so_hiwat = _TTY_BUFSIZ;
	sop->so_lowat = 256;
	putnext(rqp, mop);

	/*
	 * The input, devp, is a major device number, the output is put
	 * into the same parm as a major,minor pair.
	 */
	*devp = makedevice(getmajor(*devp), dminor);

	return (0);
}


/*
 * Find the address to private data identifying the subsidiary's write queue.
 * Send a hang-up message up the subsidiary's read queue to designate the
 * manager/subsidiary pair is tearing down. Uattach the manager and subsidiary
 * by nulling out the write queue fields in the private data structure.
 * Finally, unlock the manager/subsidiary pair and mark the manager as closed.
 */
static int
ptmclose(queue_t *rqp, int flag, cred_t *credp)
{
	struct pt_ttys	*ptmp;
	queue_t *pts_rdq;

	ASSERT(rqp->q_ptr);

	ptmp = (struct pt_ttys *)rqp->q_ptr;
	PT_ENTER_READ(ptmp);
	if (ptmp->pts_rdq) {
		pts_rdq = ptmp->pts_rdq;
		if (pts_rdq->q_next) {
			DBG(("send hangup message to subsidiary\n"));
			(void) putnextctl(pts_rdq, M_HANGUP);
		}
	}
	PT_EXIT_READ(ptmp);
	/*
	 * ptm_rdq should be cleared before call to qprocsoff() to prevent pts
	 * write procedure to attempt using ptm_rdq after qprocsoff.
	 */
	PT_ENTER_WRITE(ptmp);
	ptmp->ptm_rdq = NULL;
	freemsg(ptmp->pt_nullmsg);
	ptmp->pt_nullmsg = NULL;
	/*
	 * qenable subsidiary side write queue so that it can flush
	 * its messages as manager's read queue is going away
	 */
	if (ptmp->pts_rdq)
		qenable(WR(ptmp->pts_rdq));
	PT_EXIT_WRITE(ptmp);

	qprocsoff(rqp);

	/* Finish the close */
	rqp->q_ptr = NULL;
	WR(rqp)->q_ptr = NULL;

	ptms_close(ptmp, PTMOPEN | PTLOCK);

	return (0);
}

/*
 * The wput procedure will only handle ioctl and flush messages.
 */
static int
ptmwput(queue_t *qp, mblk_t *mp)
{
	struct pt_ttys	*ptmp;
	struct iocblk	*iocp;

	DBG(("entering ptmwput\n"));
	ASSERT(qp->q_ptr);

	ptmp = (struct pt_ttys *)qp->q_ptr;
	PT_ENTER_READ(ptmp);

	switch (mp->b_datap->db_type) {
	/*
	 * If this is a write queue request, flush manager's write queue and
	 * send FLUSHR up subsidiary side.  If it is a read queue request,
	 * convert to FLUSHW and putnext().
	 */
	case M_FLUSH:
		{
			unsigned char flush_flg = 0;

			DBG(("ptm got flush request\n"));
			if (*mp->b_rptr & FLUSHW) {
				DBG(("got FLUSHW, flush ptm write Q\n"));
				if (*mp->b_rptr & FLUSHBAND) {
					/*
					 * if it is a FLUSHBAND, do flushband.
					 */
					flushband(qp, *(mp->b_rptr + 1),
					    FLUSHDATA);
				} else {
					flushq(qp, FLUSHDATA);
				}
				flush_flg = (*mp->b_rptr & ~FLUSHW) | FLUSHR;
			}
			if (*mp->b_rptr & FLUSHR) {
				DBG(("got FLUSHR, set FLUSHW\n"));
				flush_flg |= (*mp->b_rptr & ~FLUSHR) | FLUSHW;
			}
			if (flush_flg != 0 && ptmp->pts_rdq &&
			    !(ptmp->pt_state & PTLOCK)) {
				DBG(("putnext to pts\n"));
				*mp->b_rptr = flush_flg;
				putnext(ptmp->pts_rdq, mp);
			} else {
				freemsg(mp);
			}
			break;
		}

	case M_IOCTL:
		iocp = (struct iocblk *)mp->b_rptr;
		switch (iocp->ioc_cmd) {
		default:
			if ((ptmp->pt_state & PTLOCK) ||
			    (ptmp->pts_rdq == NULL)) {
				DBG(("got M_IOCTL but no subsidiary\n"));
				miocnak(qp, mp, 0, EINVAL);
				PT_EXIT_READ(ptmp);
				return (0);
			}
			(void) putq(qp, mp);
			break;
		case UNLKPT:
			mutex_enter(&ptmp->pt_lock);
			ptmp->pt_state &= ~PTLOCK;
			mutex_exit(&ptmp->pt_lock);
			/*FALLTHROUGH*/
		case ISPTM:
			DBG(("ack the UNLKPT/ISPTM\n"));
			miocack(qp, mp, 0, 0);
			break;
		case PTSSTTY:
			mutex_enter(&ptmp->pt_lock);
			ptmp->pt_state |= PTSTTY;
			mutex_exit(&ptmp->pt_lock);
			DBG(("ack PTSSTTY\n"));
			miocack(qp, mp, 0, 0);
			break;
		case ZONEPT:
		{
			zoneid_t z;
			int error;

			if ((error = drv_priv(iocp->ioc_cr)) != 0) {
				miocnak(qp, mp, 0, error);
				break;
			}
			if ((error = miocpullup(mp, sizeof (zoneid_t))) != 0) {
				miocnak(qp, mp, 0, error);
				break;
			}
			z = *((zoneid_t *)mp->b_cont->b_rptr);
			if (z < MIN_ZONEID || z > MAX_ZONEID) {
				miocnak(qp, mp, 0, EINVAL);
				break;
			}

			mutex_enter(&ptmp->pt_lock);
			ptmp->pt_zoneid = z;
			mutex_exit(&ptmp->pt_lock);
			miocack(qp, mp, 0, 0);
			break;
		}
		case OWNERPT:
		{
			pt_own_t *ptop;
			int error;
			zone_t *zone;

			if ((error = miocpullup(mp, sizeof (pt_own_t))) != 0) {
				miocnak(qp, mp, 0, error);
				break;
			}

			zone = zone_find_by_id(ptmp->pt_zoneid);
			ptop = (pt_own_t *)mp->b_cont->b_rptr;

			if (!VALID_UID(ptop->pto_ruid, zone) ||
			    !VALID_GID(ptop->pto_rgid, zone)) {
				zone_rele(zone);
				miocnak(qp, mp, 0, EINVAL);
				break;
			}
			zone_rele(zone);
			mutex_enter(&ptmp->pt_lock);
			ptmp->pt_ruid = ptop->pto_ruid;
			ptmp->pt_rgid = ptop->pto_rgid;
			mutex_exit(&ptmp->pt_lock);
			miocack(qp, mp, 0, 0);
			break;
		}
		}
		break;

	case M_READ:
		/* Caused by ldterm - can not pass to subsidiary */
		freemsg(mp);
		break;

	/*
	 * Send other messages to the subsidiary:
	 */
	default:
		if ((ptmp->pt_state & PTLOCK) || (ptmp->pts_rdq == NULL)) {
			DBG(("got msg. but no subsidiary\n"));
			mp = mexchange(NULL, mp, 2, M_ERROR, -1);
			if (mp != NULL) {
				mp->b_rptr[0] = NOERROR;
				mp->b_rptr[1] = EINVAL;
				qreply(qp, mp);
			}
			PT_EXIT_READ(ptmp);
			return (0);
		}
		DBG(("put msg on manager's write queue\n"));
		(void) putq(qp, mp);
		break;
	}
	DBG(("return from ptmwput()\n"));
	PT_EXIT_READ(ptmp);
	return (0);
}


/*
 * Enable the write side of the subsidiary.  This triggers the subsidiary to
 * send any messages queued on its write side to the read side of this manager.
 */
static int
ptmrsrv(queue_t *qp)
{
	struct pt_ttys	*ptmp;

	DBG(("entering ptmrsrv\n"));
	ASSERT(qp->q_ptr);

	ptmp = (struct pt_ttys *)qp->q_ptr;
	PT_ENTER_READ(ptmp);
	if (ptmp->pts_rdq) {
		qenable(WR(ptmp->pts_rdq));
	}
	PT_EXIT_READ(ptmp);
	DBG(("leaving ptmrsrv\n"));
	return (0);
}


/*
 * If there are messages on this queue that can be sent to subsidiary, send
 * them via putnext().  Otherwise, if queued messages cannot be sent, leave
 * them on this queue.  If priority messages on this queue, send them to the
 * subsidiary no matter what.
 */
static int
ptmwsrv(queue_t *qp)
{
	struct pt_ttys	*ptmp;
	mblk_t		*mp;

	DBG(("entering ptmwsrv\n"));
	ASSERT(qp->q_ptr);

	ptmp = (struct pt_ttys *)qp->q_ptr;

	if ((mp = getq(qp)) == NULL) {
		/* If there are no messages there's nothing to do. */
		DBG(("leaving ptmwsrv (no messages)\n"));
		return (0);
	}

	PT_ENTER_READ(ptmp);
	if ((ptmp->pt_state  & PTLOCK) || (ptmp->pts_rdq == NULL)) {
		DBG(("in manager write srv proc but no subsidiary\n"));
		/*
		 * Free messages on the write queue and send
		 * NAK for any M_IOCTL type messages to wakeup
		 * the user process waiting for ACK/NAK from
		 * the ioctl invocation
		 */
		do {
			if (mp->b_datap->db_type == M_IOCTL)
				miocnak(qp, mp, 0, EINVAL);
			else
				freemsg(mp);
		} while ((mp = getq(qp)) != NULL);
		flushq(qp, FLUSHALL);

		mp = mexchange(NULL, NULL, 2, M_ERROR, -1);
		if (mp != NULL) {
			mp->b_rptr[0] = NOERROR;
			mp->b_rptr[1] = EINVAL;
			qreply(qp, mp);
		}
		PT_EXIT_READ(ptmp);
		return (0);
	}
	/*
	 * While there are messages on this write queue...
	 */
	do {
		/*
		 * If this is not a control message, and we cannot put messages
		 * on the subsidiary's read queue, put it back on this queue.
		 */
		if (mp->b_datap->db_type <= QPCTL &&
		    !bcanputnext(ptmp->pts_rdq, mp->b_band)) {
			DBG(("put msg. back on queue\n"));
			(void) putbq(qp, mp);
			break;
		}
		/*
		 * Otherwise send the message up subsidiary's stream
		 */
		DBG(("send message to subsidiary\n"));
		putnext(ptmp->pts_rdq, mp);
	} while ((mp = getq(qp)) != NULL);
	DBG(("leaving ptmwsrv\n"));
	PT_EXIT_READ(ptmp);
	return (0);
}