sys_procdesc.c

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/*-
 * Copyright (c) 2009 Robert N. M. Watson
 * All rights reserved.
 *
 * This software was developed at the University of Cambridge Computer
 * Laboratory with support from a grant from Google, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*-
 * FreeBSD process descriptor facility.
 *
 * Some processes are represented by a file descriptor, which will be used in
 * preference to signaling and pids for the purposes of process management,
 * and is, in effect, a form of capability.  When a process descriptor is
 * used with a process, it ceases to be visible to certain traditional UNIX
 * process facilities, such as waitpid(2).
 *
 * Some semantics:
 *
 * - At most one process descriptor will exist for any process, although
 *   references to that descriptor may be held from many processes (or even
 *   be in flight between processes over a local domain socket).
 * - Last close on the process descriptor will terminate the process using
 *   SIGKILL and reparent it to init so that there's a process to reap it
 *   when it's done exiting.
 * - If the process exits before the descriptor is closed, it will not
 *   generate SIGCHLD on termination, or be picked up by waitpid().
 * - The pdkill(2) system call may be used to deliver a signal to the process
 *   using its process descriptor.
 * - The pdwait4(2) system call may be used to block (or not) on a process
 *   descriptor to collect termination information.
 *
 * Open questions:
 *
 * - How to handle ptrace(2)?
 * - Will we want to add a pidtoprocdesc(2) system call to allow process
 *   descriptors to be created for processes without pfork(2)?
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include "opt_procdesc.h"

#include <sys/param.h>
#include <sys/capability.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/poll.h>
#include <sys/proc.h>
#include <sys/procdesc.h>
#include <sys/resourcevar.h>
#include <sys/stat.h>
#include <sys/sysproto.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/ucred.h>

#include <security/audit/audit.h>

#include <vm/uma.h>

#ifdef PROCDESC

FEATURE(process_descriptors, "Process Descriptors");

static uma_zone_t procdesc_zone;

static fo_rdwr_t        procdesc_read;
static fo_rdwr_t        procdesc_write;
static fo_truncate_t    procdesc_truncate;
static fo_ioctl_t       procdesc_ioctl;
static fo_poll_t        procdesc_poll;
static fo_kqfilter_t    procdesc_kqfilter;
static fo_stat_t        procdesc_stat;
static fo_close_t       procdesc_close;
static fo_chmod_t       procdesc_chmod;
static fo_chown_t       procdesc_chown;

static struct fileops procdesc_ops = {
        .fo_read = procdesc_read,
        .fo_write = procdesc_write,
        .fo_truncate = procdesc_truncate,
        .fo_ioctl = procdesc_ioctl,
        .fo_poll = procdesc_poll,
        .fo_kqfilter = procdesc_kqfilter,
        .fo_stat = procdesc_stat,
        .fo_close = procdesc_close,
        .fo_chmod = procdesc_chmod,
        .fo_chown = procdesc_chown,
        .fo_flags = DFLAG_PASSABLE,
};

/*
 * Initialize with VFS so that process descriptors are available along with
 * other file descriptor types.  As long as it runs before init(8) starts,
 * there shouldn't be a problem.
 */
static void
procdesc_init(void *dummy __unused)
{

        procdesc_zone = uma_zcreate("procdesc", sizeof(struct procdesc),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
        if (procdesc_zone == NULL)
                panic("procdesc_init: procdesc_zone not initialized");
}
SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, procdesc_init, NULL);

/*
 * Return a locked process given a process descriptor, or ESRCH if it has
 * died.
 */
int
procdesc_find(struct thread *td, int fd, cap_rights_t rights,
    struct proc **p)
{
        struct procdesc *pd;
        struct file *fp;
        int error;

        error = fget(td, fd, rights, &fp);
        if (error)
                return (error);
        if (fp->f_type != DTYPE_PROCDESC) {
                error = EBADF;
                goto out;
        }
        pd = fp->f_data;
        sx_slock(&proctree_lock);
        if (pd->pd_proc != NULL) {
                *p = pd->pd_proc;
                PROC_LOCK(*p);
        } else
                error = ESRCH;
        sx_sunlock(&proctree_lock);
out:
        fdrop(fp, td);
        return (error);
}

/*
 * Function to be used by procstat(1) sysctls when returning procdesc
 * information.
 */
pid_t
procdesc_pid(struct file *fp_procdesc)
{
        struct procdesc *pd;

        KASSERT(fp_procdesc->f_type == DTYPE_PROCDESC,
           ("procdesc_pid: !procdesc"));

        pd = fp_procdesc->f_data;
        return (pd->pd_pid);
}

/*
 * Retrieve the PID associated with a process descriptor.
 */
int
kern_pdgetpid(struct thread *td, int fd, cap_rights_t rights, pid_t *pidp)
{
        struct file *fp;
        int error;

        error = fget(td, fd, rights, &fp);
        if (error)
                return (error);
        if (fp->f_type != DTYPE_PROCDESC) {
                error = EBADF;
                goto out;
        }
        *pidp = procdesc_pid(fp);
out:
        fdrop(fp, td);
        return (error);
}

/*
 * System call to return the pid of a process given its process descriptor.
 */
int
sys_pdgetpid(struct thread *td, struct pdgetpid_args *uap)
{
        pid_t pid;
        int error;

        AUDIT_ARG_FD(uap->fd);
        error = kern_pdgetpid(td, uap->fd, CAP_PDGETPID, &pid);
        if (error == 0)
                error = copyout(&pid, uap->pidp, sizeof(pid));
        return (error);
}

/*
 * When a new process is forked by pdfork(), a file descriptor is allocated
 * by the fork code first, then the process is forked, and then we get a
 * chance to set up the process descriptor.  Failure is not permitted at this
 * point, so procdesc_new() must succeed.
 */
void
procdesc_new(struct proc *p, int flags)
{
        struct procdesc *pd;

        pd = uma_zalloc(procdesc_zone, M_WAITOK | M_ZERO);
        pd->pd_proc = p;
        pd->pd_pid = p->p_pid;
        p->p_procdesc = pd;
        pd->pd_flags = 0;
        if (flags & PD_DAEMON)
                pd->pd_flags |= PDF_DAEMON;
        PROCDESC_LOCK_INIT(pd);

        /*
         * Process descriptors start out with two references: one from their
         * struct file, and the other from their struct proc.
         */
        refcount_init(&pd->pd_refcount, 2);
}

/*
 * Initialize a file with a process descriptor.
 */
void
procdesc_finit(struct procdesc *pdp, struct file *fp)
{

        finit(fp, FREAD | FWRITE, DTYPE_PROCDESC, pdp, &procdesc_ops);
}

static void
procdesc_free(struct procdesc *pd)
{

        /*
         * When the last reference is released, we assert that the descriptor
         * has been closed, but not that the process has exited, as we will
         * detach the descriptor before the process dies if the descript is
         * closed, as we can't wait synchronously.
         */
        if (refcount_release(&pd->pd_refcount)) {
                KASSERT(pd->pd_proc == NULL,
                    ("procdesc_free: pd_proc != NULL"));
                KASSERT((pd->pd_flags & PDF_CLOSED),
                    ("procdesc_free: !PDF_CLOSED"));

                PROCDESC_LOCK_DESTROY(pd);
                uma_zfree(procdesc_zone, pd);
        }
}

/*
 * procdesc_exit() - notify a process descriptor that its process is exiting.
 * We use the proctree_lock to ensure that process exit either happens
 * strictly before or strictly after a concurrent call to procdesc_close().
 */
int
procdesc_exit(struct proc *p)
{
        struct procdesc *pd;

        sx_assert(&proctree_lock, SA_XLOCKED);
        PROC_LOCK_ASSERT(p, MA_OWNED);
        KASSERT(p->p_procdesc != NULL, ("procdesc_exit: p_procdesc NULL"));

        pd = p->p_procdesc;

        PROCDESC_LOCK(pd);
        KASSERT((pd->pd_flags & PDF_CLOSED) == 0 || p->p_pptr == initproc,
            ("procdesc_exit: closed && parent not init"));

        pd->pd_flags |= PDF_EXITED;

        /*
         * If the process descriptor has been closed, then we have nothing
         * to do; return 1 so that init will get SIGCHLD and do the reaping.
         * Clean up the procdesc now rather than letting it happen during
         * that reap.
         */
        if (pd->pd_flags & PDF_CLOSED) {
                PROCDESC_UNLOCK(pd);
                pd->pd_proc = NULL;
                p->p_procdesc = NULL;
                procdesc_free(pd);
                return (1);
        }
        if (pd->pd_flags & PDF_SELECTED) {
                pd->pd_flags &= ~PDF_SELECTED;
                selwakeup(&pd->pd_selinfo);
        }
        PROCDESC_UNLOCK(pd);
        return (0);
}

/*
 * When a process descriptor is reaped, perhaps as a result of close() or
 * pdwait4(), release the process's reference on the process descriptor.
 */
void
procdesc_reap(struct proc *p)
{
        struct procdesc *pd;

        sx_assert(&proctree_lock, SA_XLOCKED);
        KASSERT(p->p_procdesc != NULL, ("procdesc_reap: p_procdesc == NULL"));

        pd = p->p_procdesc;
        pd->pd_proc = NULL;
        procdesc_free(pd);
}

/*
 * procdesc_close() - last close on a process descriptor.  If the process is
 * still running, terminate with SIGKILL (unless PD_DAEMON is set) and let
 * init(8) clean up the mess; if not, we have to clean up the zombie ourselves.
 */
static int
procdesc_close(struct file *fp, struct thread *td)
{
        struct procdesc *pd;
        struct proc *p;

        KASSERT(fp->f_type == DTYPE_PROCDESC, ("procdesc_close: !procdesc"));

        pd = fp->f_data;
        fp->f_ops = &badfileops;
        fp->f_data = NULL;

        sx_xlock(&proctree_lock);
        PROCDESC_LOCK(pd);
        pd->pd_flags |= PDF_CLOSED;
        PROCDESC_UNLOCK(pd);
        p = pd->pd_proc;
        PROC_LOCK(p);
        if (p->p_state == PRS_ZOMBIE) {
                /*
                 * If the process is already dead and just awaiting reaping,
                 * do that now.  This will release the process's reference to
                 * the process descriptor when it calls back into
                 * procdesc_reap().
                 */
                PROC_SLOCK(p);
                proc_reap(curthread, p, NULL, 0);
        } else {
                /*
                 * If the process is not yet dead, we need to kill it, but we
                 * can't wait around synchronously for it to go away, as that
                 * path leads to madness (and deadlocks).  First, detach the
                 * process from its descriptor so that its exit status will
                 * be reported normally.
                 */
                pd->pd_proc = NULL;
                p->p_procdesc = NULL;
                procdesc_free(pd);

                /*
                 * Next, reparent it to init(8) so that there's someone to
                 * pick up the pieces; finally, terminate with prejudice.
                 */
                p->p_sigparent = SIGCHLD;
                proc_reparent(p, initproc);
                if ((pd->pd_flags & PD_DAEMON) == 0)
                        kern_psignal(p, SIGKILL);
                PROC_UNLOCK(p);
                sx_xunlock(&proctree_lock);
        }

        /*
         * Release the file descriptor's reference on the process descriptor.
         */
        procdesc_free(pd);
        return (0);
}

static int
procdesc_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{

        return (EOPNOTSUPP);
}

static int
procdesc_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
    int flags, struct thread *td)
{

        return (EOPNOTSUPP);
}

static int
procdesc_truncate(struct file *fp, off_t length, struct ucred *active_cred,
    struct thread *td)
{

        return (EOPNOTSUPP);
}

static int
procdesc_ioctl(struct file *fp, u_long com, void *data,
    struct ucred *active_cred, struct thread *td)
{

        return (EOPNOTSUPP);
}

static int
procdesc_poll(struct file *fp, int events, struct ucred *active_cred,
    struct thread *td)
{
        struct procdesc *pd;
        int revents;

        revents = 0;
        pd = fp->f_data;
        PROCDESC_LOCK(pd);
        if (pd->pd_flags & PDF_EXITED)
                revents |= POLLHUP;
        if (revents == 0) {
                selrecord(td, &pd->pd_selinfo);
                pd->pd_flags |= PDF_SELECTED;
        }
        PROCDESC_UNLOCK(pd);
        return (revents);
}

static int
procdesc_kqfilter(struct file *fp, struct knote *kn)
{

        return (EOPNOTSUPP);
}

static int
procdesc_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
    struct thread *td)
{
        struct procdesc *pd;
        struct timeval pstart;

        /*
         * XXXRW: Perhaps we should cache some more information from the
         * process so that we can return it reliably here even after it has
         * died.  For example, caching its credential data.
         */
        bzero(sb, sizeof(*sb));
        pd = fp->f_data;
        sx_slock(&proctree_lock);
        if (pd->pd_proc != NULL) {
                PROC_LOCK(pd->pd_proc);

                /* Set birth and [acm] times to process start time. */
                pstart = pd->pd_proc->p_stats->p_start;
                timevaladd(&pstart, &boottime);
                TIMEVAL_TO_TIMESPEC(&pstart, &sb->st_birthtim);
                sb->st_atim = sb->st_birthtim;
                sb->st_ctim = sb->st_birthtim;
                sb->st_mtim = sb->st_birthtim;
                if (pd->pd_proc->p_state != PRS_ZOMBIE)
                        sb->st_mode = S_IFREG | S_IRWXU;
                else
                        sb->st_mode = S_IFREG;
                sb->st_uid = pd->pd_proc->p_ucred->cr_ruid;
                sb->st_gid = pd->pd_proc->p_ucred->cr_rgid;
                PROC_UNLOCK(pd->pd_proc);
        } else
                sb->st_mode = S_IFREG;
        sx_sunlock(&proctree_lock);
        return (0);
}

static int
procdesc_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
    struct thread *td)
{

        return (EOPNOTSUPP);
}

static int
procdesc_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
    struct thread *td)
{

        return (EOPNOTSUPP);
}

#else /* !PROCDESC */

int
sys_pdgetpid(struct thread *td, struct pdgetpid_args *uap)
{

        return (ENOSYS);
}

#endif /* PROCDESC */