/*
 * 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 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright 2012 Milan Jurik. All rights reserved.
 * Copyright 2019 Joyent, Inc.
 */

/*      Copyright (c) 1988 AT&T */
/*        All Rights Reserved   */


/* from S5R4 1.6 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/sysmacros.h>
#include <sys/signal.h>
#include <sys/cred.h>
#include <sys/user.h>
#include <sys/errno.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <sys/cmn_err.h>
#include <sys/debug.h>
#include <sys/pathname.h>
#include <sys/disp.h>
#include <sys/exec.h>
#include <sys/kmem.h>
#include <sys/note.h>
#include <sys/sdt.h>

/*
 * This is the loadable module wrapper.
 */
#include <sys/modctl.h>

extern int intpexec(struct vnode *, struct execa *, struct uarg *,
    struct intpdata *, int, size_t *, int, caddr_t, struct cred *, int);

static struct execsw esw = {
        intpmagicstr,
        0,
        2,
        intpexec,
        NULL
};

/*
 * Module linkage information for the kernel.
 */
extern struct mod_ops mod_execops;

static struct modlexec modlexec = {
        &mod_execops, "exec mod for interp", &esw
};

static struct modlinkage modlinkage = {
        MODREV_1, (void *)&modlexec, NULL
};

int
_init()
{
        return (mod_install(&modlinkage));
}

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

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


/*
 * Crack open a '#!' line.
 */
static int
getintphead(struct vnode *vp, struct intpdata *idatap)
{
        int error;
        char *cp, *linep = idatap->intp;
        ssize_t resid;

        /*
         * Read the entire line and confirm that it starts with '#!'.
         */
        if (error = vn_rdwr(UIO_READ, vp, linep, INTPSZ, (offset_t)0,
            UIO_SYSSPACE, 0, (rlim64_t)0, CRED(), &resid))
                return (error);
        if (resid > INTPSZ-2 || linep[0] != '#' || linep[1] != '!')
                return (ENOEXEC);
        /*
         * Blank all white space and find the newline.
         */
        for (cp = &linep[2]; cp < &linep[INTPSZ] && *cp != '\n'; cp++)
                if (*cp == '\t')
                        *cp = ' ';
        if (cp >= &linep[INTPSZ])
                return (ENOEXEC);
        ASSERT(*cp == '\n');
        *cp = '\0';

        /*
         * Locate the beginning and end of the interpreter name.
         * In addition to the name, one additional argument may
         * optionally be included here, to be prepended to the
         * arguments provided on the command line.  Thus, for
         * example, you can say
         *
         *      #! /usr/bin/awk -f
         */
        for (cp = &linep[2]; *cp == ' '; cp++)
                ;
        if (*cp == '\0')
                return (ENOEXEC);
        idatap->intp_name[0] = cp;
        while (*cp && *cp != ' ')
                cp++;
        if (*cp == '\0') {
                idatap->intp_arg[0] = NULL;
        } else {
                *cp++ = '\0';
                while (*cp == ' ')
                        cp++;
                if (*cp == '\0')
                        idatap->intp_arg[0] = NULL;
                else {
                        idatap->intp_arg[0] = cp;
                        while (*cp && *cp != ' ')
                                cp++;
                        *cp = '\0';
                }
        }
        return (0);
}

/*
 * We support nested interpreters up to a depth of INTP_MAXDEPTH (this value
 * matches the depth on Linux). When a nested interpreter is in use, the
 * previous name and argument must be passed along. We use the intpdata_t
 * name and argument arrays for this. In the normal, non-nested case, only the
 * first element in those arrays will be populated.
 *
 * For setid scripts the "script hole" is a security race condition between
 * when we exec the interpreter and when the interpreter reads the script. We
 * handle this below for the initial script, but we don't allow setid scripts
 * when using nested interpreters. Because gexec only modifies the credentials
 * for a setid script at level 0, then if we come back through for a nested
 * interpreter we know that args->fname will be set (the first script is setid)
 * and we can return an error. If an intermediate nested interpreter is setid
 * then it will not be run with different credentials because of the gexec
 * handling, so it is effectively no longer setid and we don't have to worry
 * about the "script hole".
 */
int
intpexec(
        struct vnode *vp,
        struct execa *uap,
        struct uarg *args,
        struct intpdata *idatap,
        int level,
        size_t *execsz,
        int setid,
        caddr_t exec_file,
        struct cred *cred,
        int brand_action)
{
        _NOTE(ARGUNUSED(brand_action))
        vnode_t *nvp;
        int error = 0;
        struct intpdata idata;
        struct pathname intppn;
        struct pathname resolvepn;
        char *opath;
        char devfd[19]; /* 32-bit int fits in 10 digits + 8 for "/dev/fd/" */
        int fd = -1;

        if (level >= INTP_MAXDEPTH) {   /* Can't recurse past maxdepth */
                error = ELOOP;
                goto bad;
        }

        if (level == 0)
                ASSERT(idatap == (struct intpdata *)NULL);

        bzero(&idata, sizeof (intpdata_t));

        /*
         * Allocate a buffer to read in the interpreter pathname.
         */
        idata.intp = kmem_alloc(INTPSZ, KM_SLEEP);
        if (error = getintphead(vp, &idata))
                goto fail;

        /*
         * Look the new vnode up.
         */
        if (error = pn_get(idata.intp_name[0], UIO_SYSSPACE, &intppn))
                goto fail;
        pn_alloc(&resolvepn);
        if (error = lookuppn(&intppn, &resolvepn, FOLLOW, NULLVPP, &nvp)) {
                pn_free(&resolvepn);
                pn_free(&intppn);
                goto fail;
        }

        if (level > 0) {
                /*
                 * We have a nested interpreter. The previous name(s) and
                 * argument(s) need to be passed along. We also keep track
                 * of how often this zone uses nested interpreters.
                 */
                int i;

                atomic_inc_32(&curproc->p_zone->zone_nested_intp);

                ASSERT(idatap != NULL);
                /* since we're shifting up, loop stops one short */
                for (i = 0; i < (INTP_MAXDEPTH - 1); i++) {
                        idata.intp_name[i + 1] = idatap->intp_name[i];
                        idata.intp_arg[i + 1] = idatap->intp_arg[i];
                }

                DTRACE_PROBE3(nested__intp, int, level, void *, &idata,
                    void *, nvp);
        }

        opath = args->pathname;
        args->pathname = resolvepn.pn_path;
        /* don't free resolvepn until we are done with args */
        pn_free(&intppn);

        /*
         * Disallow setuid or additional privilege execution for nested
         * interpreters.
         */
        if (level > 0 && args->fname != NULL) {
                error = ENOEXEC;
                goto done;
        }

        /*
         * When we're executing a set-uid script resulting in uids
         * mismatching or when we execute with additional privileges,
         * we close the "replace script between exec and open by shell"
         * hole by passing the script as /dev/fd parameter.
         */
        if ((setid & EXECSETID_PRIVS) != 0 ||
            (setid & (EXECSETID_UGIDS|EXECSETID_SETID)) ==
            (EXECSETID_UGIDS|EXECSETID_SETID)) {
                (void) strcpy(devfd, "/dev/fd/");
                if (error = execopen(&vp, &fd))
                        goto done;
                numtos(fd, &devfd[8]);
                args->fname = devfd;
        }

        error = gexec(&nvp, uap, args, &idata, ++level, execsz, exec_file, cred,
            EBA_NONE);

        if (!error) {
                /*
                 * Close this executable as the interpreter
                 * will open and close it later on.
                 */
                (void) VOP_CLOSE(vp, FREAD, 1, (offset_t)0, cred, NULL);
        }
done:
        VN_RELE(nvp);
        args->pathname = opath;
        pn_free(&resolvepn);
fail:
        kmem_free(idata.intp, INTPSZ);
        if (error && fd != -1)
                (void) execclose(fd);
bad:
        return (error);
}