6198 Let's EOL cachefs

[illumos-gate.git] / usr / src / uts / common / os / session.c

/*
 * 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 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*      Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
/*        All Rights Reserved   */


#pragma ident   "%Z%%M% %I%     %E% SMI"

#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/file.h>
#include <sys/vnode.h>
#include <sys/errno.h>
#include <sys/signal.h>
#include <sys/cred.h>
#include <sys/policy.h>
#include <sys/conf.h>
#include <sys/debug.h>
#include <sys/proc.h>
#include <sys/session.h>
#include <sys/kmem.h>
#include <sys/cmn_err.h>
#include <sys/strsubr.h>
#include <sys/fs/snode.h>

sess_t session0 = {
        &pid0,          /* s_sidp */
        {0},            /* s_lock */
        1,              /* s_ref */
        B_FALSE,        /* s_sighuped */
        B_FALSE,        /* s_exit */
        0,              /* s_exit_cv */
        0,              /* s_cnt */
        0,              /* s_cnt_cv */
        NODEV,          /* s_dev */
        NULL,           /* s_vp */
        NULL            /* s_cred */
};

void
sess_hold(proc_t *p)
{
        ASSERT(MUTEX_HELD(&pidlock) || MUTEX_HELD(&p->p_splock));
        mutex_enter(&p->p_sessp->s_lock);
        p->p_sessp->s_ref++;
        mutex_exit(&p->p_sessp->s_lock);
}

void
sess_rele(sess_t *sp, boolean_t pidlock_held)
{
        ASSERT(MUTEX_HELD(&pidlock) || !pidlock_held);

        mutex_enter(&sp->s_lock);

        ASSERT(sp->s_ref != 0);
        if (--sp->s_ref > 0) {
                mutex_exit(&sp->s_lock);
                return;
        }
        ASSERT(sp->s_ref == 0);

        /*
         * It's ok to free this session structure now because we know
         * that no one else can have a pointer to it.  We know this
         * to be true because the only time that s_ref can possibly
         * be incremented is when pidlock or p_splock is held AND there
         * is a proc_t that points to that session structure.  In that
         * case we are guaranteed that the s_ref is at least 1 since there
         * is a proc_t that points to it.  So when s_ref finally drops to
         * zero then no one else has a reference (and hence pointer) to
         * this session structure and there is no valid proc_t pointing
         * to this session structure anymore so, no one can acquire a
         * reference (and pointer) to this session structure so it's
         * ok to free it here.
         */

        if (sp == &session0)
                panic("sp == &session0");

        /* make sure there are no outstanding holds */
        ASSERT(sp->s_cnt == 0);

        /* make sure there is no exit in progress */
        ASSERT(!sp->s_exit);

        /* make sure someone already freed any ctty */
        ASSERT(sp->s_vp == NULL);
        ASSERT(sp->s_dev == NODEV);

        if (!pidlock_held)
                mutex_enter(&pidlock);
        PID_RELE(sp->s_sidp);
        if (!pidlock_held)
                mutex_exit(&pidlock);

        mutex_destroy(&sp->s_lock);
        cv_destroy(&sp->s_cnt_cv);
        kmem_free(sp, sizeof (sess_t));
}

sess_t *
tty_hold(void)
{
        proc_t          *p = curproc;
        sess_t          *sp;
        boolean_t       got_sig = B_FALSE;

        /* make sure the caller isn't holding locks they shouldn't */
        ASSERT(MUTEX_NOT_HELD(&pidlock));

        for (;;) {
                mutex_enter(&p->p_splock);      /* protect p->p_sessp */
                sp = p->p_sessp;
                mutex_enter(&sp->s_lock);       /* protect sp->* */

                /* make sure the caller isn't holding locks they shouldn't */
                ASSERT((sp->s_vp == NULL) ||
                    MUTEX_NOT_HELD(&sp->s_vp->v_stream->sd_lock));

                /*
                 * If the session leader process is not exiting (and hence
                 * not trying to release the session's ctty) then we can
                 * safely grab a hold on the current session structure
                 * and return it.  If on the other hand the session leader
                 * process is exiting and clearing the ctty then we'll
                 * wait till it's done before we loop around and grab a
                 * hold on the session structure.
                 */
                if (!sp->s_exit)
                        break;

                /* need to hold the session so it can't be freed */
                sp->s_ref++;
                mutex_exit(&p->p_splock);

                /* Wait till the session leader is done */
                if (!cv_wait_sig(&sp->s_exit_cv, &sp->s_lock))
                        got_sig = B_TRUE;

                /*
                 * Now we need to drop our hold on the session structure,
                 * but we can't hold any locks when we do this because
                 * sess_rele() may need to acquire pidlock.
                 */
                mutex_exit(&sp->s_lock);
                sess_rele(sp, B_FALSE);

                if (got_sig)
                        return (NULL);
        }

        /* whew, we finally got a hold */
        sp->s_cnt++;
        sp->s_ref++;
        mutex_exit(&sp->s_lock);
        mutex_exit(&p->p_splock);
        return (sp);
}

void
tty_rele(sess_t *sp)
{
        /* make sure the caller isn't holding locks they shouldn't */
        ASSERT(MUTEX_NOT_HELD(&pidlock));

        mutex_enter(&sp->s_lock);
        if ((--sp->s_cnt) == 0)
                cv_broadcast(&sp->s_cnt_cv);
        mutex_exit(&sp->s_lock);

        sess_rele(sp, B_FALSE);
}

void
sess_create(void)
{
        proc_t *p = curproc;
        sess_t *sp, *old_sp;

        sp = kmem_zalloc(sizeof (sess_t), KM_SLEEP);

        mutex_init(&sp->s_lock, NULL, MUTEX_DEFAULT, NULL);
        cv_init(&sp->s_cnt_cv, NULL, CV_DEFAULT, NULL);

        /*
         * we need to grap p_lock to protect p_pgidp because
         * /proc looks at p_pgidp while holding only p_lock.
         *
         * we don't need to hold p->p_sessp->s_lock or get a hold on the
         * session structure since we're not actually updating any of
         * the contents of the old session structure.
         */
        mutex_enter(&pidlock);
        mutex_enter(&p->p_lock);
        mutex_enter(&p->p_splock);

        pgexit(p);

        sp->s_sidp = p->p_pidp;
        sp->s_ref = 1;
        sp->s_dev = NODEV;

        old_sp = p->p_sessp;
        p->p_sessp = sp;

        pgjoin(p, p->p_pidp);
        PID_HOLD(p->p_pidp);

        mutex_exit(&p->p_splock);
        mutex_exit(&p->p_lock);
        mutex_exit(&pidlock);

        sess_rele(old_sp, B_FALSE);
}

/*
 * Note that sess_ctty_clear() resets all the fields in the session
 * structure but doesn't release any holds or free any objects
 * that the session structure might currently point to.  it is the
 * callers responsibility to do this.
 */
static void
sess_ctty_clear(sess_t *sp, stdata_t *stp)
{
        /*
         * Assert that we hold all the necessary locks.  We also need
         * to be holding proc_t->p_splock for the process associated
         * with this session, but since we don't have a proc pointer
         * passed in we can't assert this here.
         */
        ASSERT(MUTEX_HELD(&stp->sd_lock) && MUTEX_HELD(&pidlock) &&
            MUTEX_HELD(&sp->s_lock));

        /* reset the session structure members to defaults */
        sp->s_sighuped = B_FALSE;
        sp->s_dev = NODEV;
        sp->s_vp = NULL;
        sp->s_cred = NULL;

        /* reset the stream session and group pointers */
        stp->sd_pgidp = NULL;
        stp->sd_sidp = NULL;
}

static void
sess_ctty_set(proc_t *p, sess_t *sp, stdata_t *stp)
{
        cred_t  *crp;

        /* Assert that we hold all the necessary locks. */
        ASSERT(MUTEX_HELD(&stp->sd_lock) && MUTEX_HELD(&pidlock) &&
            MUTEX_HELD(&p->p_splock) && MUTEX_HELD(&sp->s_lock));

        /* get holds on structures */
        mutex_enter(&p->p_crlock);
        crhold(crp = p->p_cred);
        mutex_exit(&p->p_crlock);
        PID_HOLD(sp->s_sidp);   /* requires pidlock */
        PID_HOLD(sp->s_sidp);   /* requires pidlock */

        /* update the session structure members */
        sp->s_vp = makectty(stp->sd_vnode);
        sp->s_dev = sp->s_vp->v_rdev;
        sp->s_cred = crp;

        /* update the stream emebers */
        stp->sd_flag |= STRISTTY;       /* just to be sure */
        stp->sd_sidp = sp->s_sidp;
        stp->sd_pgidp = sp->s_sidp;
}

int
strctty(stdata_t *stp)
{
        sess_t          *sp;
        proc_t          *p = curproc;
        boolean_t       got_sig = B_FALSE;

        /*
         * We are going to try to make stp the default ctty for the session
         * associated with curproc.  Not only does this require holding a
         * bunch of locks but it also requires waiting for any outstanding
         * holds on the session structure (acquired via tty_hold()) to be
         * released.  Hence, we have the following for(;;) loop that will
         * acquire our locks, do some sanity checks, and wait for the hold
         * count on the session structure to hit zero.  If we get a signal
         * while waiting for outstanding holds to be released then we abort
         * the operation and return.
         */
        for (;;) {
                mutex_enter(&stp->sd_lock);     /* protects sd_pgidp/sd_sidp */
                mutex_enter(&pidlock);          /* protects p_pidp */
                mutex_enter(&p->p_splock);      /* protects p_sessp */
                sp = p->p_sessp;
                mutex_enter(&sp->s_lock);       /* protects sp->* */

                if (((stp->sd_flag & (STRHUP|STRDERR|STWRERR|STPLEX)) != 0) ||
                    (stp->sd_sidp != NULL) ||           /* stp already ctty? */
                    (p->p_pidp != sp->s_sidp) ||        /* we're not leader? */
                    (sp->s_vp != NULL)) {               /* session has ctty? */
                        mutex_exit(&sp->s_lock);
                        mutex_exit(&p->p_splock);
                        mutex_exit(&pidlock);
                        mutex_exit(&stp->sd_lock);
                        return (ENOTTY);
                }

                /* sanity check.  we can't be exiting right now */
                ASSERT(!sp->s_exit);

                /*
                 * If no one else has a hold on this session structure
                 * then we now have exclusive access to it, so break out
                 * of this loop and update the session structure.
                 */
                if (sp->s_cnt == 0)
                        break;

                /* need to hold the session so it can't be freed */
                sp->s_ref++;

                /* ain't locking order fun? */
                mutex_exit(&p->p_splock);
                mutex_exit(&pidlock);
                mutex_exit(&stp->sd_lock);

                if (!cv_wait_sig(&sp->s_cnt_cv, &sp->s_lock))
                        got_sig = B_TRUE;
                mutex_exit(&sp->s_lock);
                sess_rele(sp, B_FALSE);

                if (got_sig)
                        return (EINTR);
        }

        /* set the session ctty bindings */
        sess_ctty_set(p, sp, stp);

        mutex_exit(&sp->s_lock);
        mutex_exit(&p->p_splock);
        mutex_exit(&pidlock);
        mutex_exit(&stp->sd_lock);
        return (0);
}

/*
 * freectty_lock() attempts to acquire the army of locks required to free
 * the ctty associated with a given session leader process.  If it returns
 * successfully the following locks will be held:
 *      sd_lock, pidlock, p_splock, s_lock
 *
 * as a secondary bit of convenience, freectty_lock() will also return
 * pointers to the session, ctty, and ctty stream associated with the
 * specified session leader process.
 */
static boolean_t
freectty_lock(proc_t *p, sess_t **spp, vnode_t **vpp, stdata_t **stpp,
    boolean_t at_exit)
{
        sess_t          *sp;
        vnode_t         *vp;
        stdata_t        *stp;

        mutex_enter(&pidlock);                  /* protect p_pidp */
        mutex_enter(&p->p_splock);              /* protect p->p_sessp */
        sp = p->p_sessp;
        mutex_enter(&sp->s_lock);               /* protect sp->* */

        if ((sp->s_sidp != p->p_pidp) ||        /* we're not leader? */
            (sp->s_vp == NULL)) {               /* no ctty? */
                mutex_exit(&sp->s_lock);
                mutex_exit(&p->p_splock);
                mutex_exit(&pidlock);
                return (B_FALSE);
        }

        vp = sp->s_vp;
        stp = sp->s_vp->v_stream;

        if (at_exit) {
                /* stop anyone else calling tty_hold() */
                sp->s_exit = B_TRUE;
        } else {
                /*
                 * due to locking order we have to grab stp->sd_lock before
                 * grabbing all the other proc/session locks.  but after we
                 * drop all our current locks it's possible that someone
                 * could come in and change our current session or close
                 * the current ctty (vp) there by making sp or stp invalid.
                 * (a VN_HOLD on vp won't protect stp because that only
                 * prevents the vnode from being freed not closed.)  so
                 * to prevent this we bump s_ref and s_cnt here.
                 *
                 * course this doesn't matter if we're the last thread in
                 * an exiting process that is the session leader, since no
                 * one else can change our session or free our ctty.
                 */
                sp->s_ref++;    /* hold the session structure */
                sp->s_cnt++;    /* protect vp and stp */
        }

        /* drop our session locks */
        mutex_exit(&sp->s_lock);
        mutex_exit(&p->p_splock);
        mutex_exit(&pidlock);

        /* grab locks in the right order */
        mutex_enter(&stp->sd_lock);             /* protects sd_pgidp/sd_sidp */
        mutex_enter(&pidlock);                  /* protect p_pidp */
        mutex_enter(&p->p_splock);              /* protects p->p_sessp */
        mutex_enter(&sp->s_lock);               /* protects sp->* */

        /* if the session has changed, abort mission */
        if (sp != p->p_sessp) {
                /*
                 * this can't happen during process exit since we're the
                 * only thread in the process and we sure didn't change
                 * our own session at this point.
                 */
                ASSERT(!at_exit);

                /* release our locks and holds */
                mutex_exit(&sp->s_lock);
                mutex_exit(&p->p_splock);
                mutex_exit(&pidlock);
                mutex_exit(&stp->sd_lock);
                tty_rele(sp);
                return (B_FALSE);
        }

        /*
         * sanity checks.  none of this should have changed since we had
         * holds on the current ctty.
         */
        ASSERT(sp->s_sidp == p->p_pidp);        /* we're the leader */
        ASSERT(sp->s_vp != NULL);               /* a ctty exists */
        ASSERT(vp == sp->s_vp);
        ASSERT(stp == sp->s_vp->v_stream);

        /* release our holds */
        if (!at_exit) {
                if ((--(sp)->s_cnt) == 0)
                        cv_broadcast(&sp->s_cnt_cv);
                sp->s_ref--;
                ASSERT(sp->s_ref > 0);
        }

        /* return our pointers */
        *spp = sp;
        *vpp = vp;
        *stpp = stp;

        return (B_TRUE);
}

/*
 * Returns B_FALSE if no signal is sent to the process group associated with
 * this ctty.  Returns B_TRUE if a signal is sent to the process group.
 * If it return B_TRUE it also means that all the locks we were holding
 * were dropped so that we could send the signal.
 */
static boolean_t
freectty_signal(proc_t *p, sess_t *sp, stdata_t *stp, boolean_t at_exit)
{
        /* Assert that we hold all the necessary locks. */
        ASSERT(MUTEX_HELD(&stp->sd_lock) && MUTEX_HELD(&pidlock) &&
            MUTEX_HELD(&p->p_splock) && MUTEX_HELD(&sp->s_lock));

        /* check if we already signaled this group */
        if (sp->s_sighuped)
                return (B_FALSE);

        sp->s_sighuped = B_TRUE;

        if (!at_exit) {
                /*
                 * once again, we're about to drop our army of locks and we
                 * don't want sp or stp to be freed.  (see the comment in
                 * freectty_lock())
                 */
                sp->s_ref++;    /* hold the session structure */
                sp->s_cnt++;    /* protect vp and stp */
        }

        /* can't hold these locks while calling pgsignal() */
        mutex_exit(&sp->s_lock);
        mutex_exit(&p->p_splock);
        mutex_exit(&pidlock);

        /* signal anyone in the foreground process group */
        pgsignal(stp->sd_pgidp, SIGHUP);

        /* signal anyone blocked in poll on this stream */
        if (!(stp->sd_flag & STRHUP))
                strhup(stp);

        mutex_exit(&stp->sd_lock);

        /* release our holds */
        if (!at_exit)
                tty_rele(sp);

        return (B_TRUE);
}

int
freectty(boolean_t at_exit)
{
        proc_t          *p = curproc;
        stdata_t        *stp;
        vnode_t         *vp;
        cred_t          *cred;
        sess_t          *sp;
        struct pid      *pgidp, *sidp;
        boolean_t       got_sig = B_FALSE;

        /*
         * If the current process is a session leader we are going to
         * try to release the ctty associated our current session.  To
         * do this we need to acquire a bunch of locks, signal any
         * processes in the forground that are associated with the ctty,
         * and make sure no one has any outstanding holds on the current
         * session * structure (acquired via tty_hold()).  Hence, we have
         * the following for(;;) loop that will do all this work for
         * us and break out when the hold count on the session structure
         * hits zero.
         */
        for (;;) {
                if (!freectty_lock(p, &sp, &vp, &stp, at_exit))
                        return (EIO);

                if (freectty_signal(p, sp, stp, at_exit)) {
                        /* loop around to re-acquire locks */
                        continue;
                }

                /*
                 * Only a session leader process can free a ctty.  So if
                 * we've made it here we know we're a session leader and
                 * if we're not actively exiting it impossible for another
                 * thread in this process to be exiting.  (Because that
                 * thread would have already stopped all other threads
                 * in the current process.)
                 */
                ASSERT(at_exit || !sp->s_exit);

                /*
                 * If no one else has a hold on this session structure
                 * then we now have exclusive access to it, so break out
                 * of this loop and update the session structure.
                 */
                if (sp->s_cnt == 0)
                        break;

                if (!at_exit) {
                        /* need to hold the session so it can't be freed */
                        sp->s_ref++;
                }

                /* ain't locking order fun? */
                mutex_exit(&p->p_splock);
                mutex_exit(&pidlock);
                mutex_exit(&stp->sd_lock);

                if (at_exit) {
                        /*
                         * if we're exiting then we can't allow this operation
                         * to fail so we do a cw_wait() instead of a
                         * cv_wait_sig().  if there are threads with active
                         * holds on this ctty that are blocked, then
                         * they should only be blocked in a cv_wait_sig()
                         * and hopefully they were in the foreground process
                         * group and recieved the SIGHUP we sent above.  of
                         * course it's possible that they weren't in the
                         * foreground process group and didn't get our
                         * signal (or they could be stopped by job control
                         * in which case our signal wouldn't matter until
                         * they are restarted).  in this case we won't
                         * exit until someone else sends them a signal.
                         */
                        cv_wait(&sp->s_cnt_cv, &sp->s_lock);
                        mutex_exit(&sp->s_lock);
                        continue;
                }

                if (!cv_wait_sig(&sp->s_cnt_cv, &sp->s_lock)) {
                        got_sig = B_TRUE;
                }

                mutex_exit(&sp->s_lock);
                sess_rele(sp, B_FALSE);

                if (got_sig)
                        return (EINTR);
        }
        ASSERT(sp->s_cnt == 0);

        /* save some pointers for later */
        cred = sp->s_cred;
        pgidp = stp->sd_pgidp;
        sidp = stp->sd_sidp;

        /* clear the session ctty bindings */
        sess_ctty_clear(sp, stp);

        /* wake up anyone blocked in tty_hold() */
        if (at_exit) {
                ASSERT(sp->s_exit);
                sp->s_exit = B_FALSE;
                cv_broadcast(&sp->s_exit_cv);
        }

        /* we can drop these locks now */
        mutex_exit(&sp->s_lock);
        mutex_exit(&p->p_splock);
        mutex_exit(&pidlock);
        mutex_exit(&stp->sd_lock);

        /* This is the only remaining thread with access to this vnode */
        (void) VOP_CLOSE(vp, 0, 1, (offset_t)0, cred, NULL);
        VN_RELE(vp);
        crfree(cred);

        /* release our holds on assorted structures and return */
        mutex_enter(&pidlock);
        PID_RELE(pgidp);
        PID_RELE(sidp);
        mutex_exit(&pidlock);

        return (1);
}

/*
 *      ++++++++++++++++++++++++
 *      ++  SunOS4.1 Buyback  ++
 *      ++++++++++++++++++++++++
 *
 * vhangup: Revoke access of the current tty by all processes
 * Used by privileged users to give a "clean" terminal at login
 */
int
vhangup(void)
{
        if (secpolicy_sys_config(CRED(), B_FALSE) != 0)
                return (set_errno(EPERM));
        /*
         * This routine used to call freectty() under a condition that
         * could never happen.  So this code has never actually done
         * anything, and evidently nobody has ever noticed.
         */
        return (0);
}

dev_t
cttydev(proc_t *pp)
{
        sess_t  *sp;
        dev_t   dev;

        mutex_enter(&pp->p_splock);     /* protects p->p_sessp */
        sp = pp->p_sessp;

#ifdef DEBUG
        mutex_enter(&sp->s_lock);       /* protects sp->* */
        if (sp->s_vp == NULL)
                ASSERT(sp->s_dev == NODEV);
        else
                ASSERT(sp->s_dev != NODEV);
        mutex_exit(&sp->s_lock);
#endif /* DEBUG */

        dev = sp->s_dev;
        mutex_exit(&pp->p_splock);
        return (dev);
}

void
ctty_clear_sighuped(void)
{
        ASSERT(MUTEX_HELD(&pidlock) || MUTEX_HELD(&curproc->p_splock));
        curproc->p_sessp->s_sighuped = B_FALSE;
}