/*
 * Copyright (c) 1993, David Greenman
 * All rights reserved.
 *
 * 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: src/sys/kern/imgact_shell.c,v 1.21.2.2 2001/12/22 01:21:39 jwd Exp $
 * $DragonFly: src/sys/kern/imgact_shell.c,v 1.6 2005/02/28 05:44:52 dillon Exp $
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/sysmsg.h>
#include <sys/exec.h>
#include <sys/imgact.h>
#include <sys/kernel.h>

#if BYTE_ORDER == LITTLE_ENDIAN
#define SHELLMAGIC      0x2123 /* #! */
#else
#define SHELLMAGIC      0x2321
#endif

/*
 * Shell interpreter image activator. A interpreter name beginning
 *      at imgp->args->begin_argv is the minimal successful exit requirement.
 */
int
exec_shell_imgact(struct image_params *imgp)
{
        const char *image_header = imgp->image_header;
        const char *ihp;
        size_t length, offset;
        int error;

        /* a shell script? */
        if (((const short *) image_header)[0] != SHELLMAGIC)
                return(-1);

        /*
         * Don't allow a shell script to be the shell for a shell
         *      script. :-)
         */
        if (imgp->interpreted)
                return(ENOEXEC);

        imgp->interpreted = 1;

        /*
         * Figure out the number of bytes that need to be reserved in the
         * argument string to copy the contents of the interpreter's command
         * line into the argument string.
         */
        ihp = &image_header[2];
        offset = 0;
        while (ihp < &image_header[PAGE_SIZE]) {
                /* Skip any whitespace */
                if (*ihp == ' ' || *ihp == '\t') {
                        ++ihp;
                        continue;
                }

                /* End of line? */
                if (*ihp == '\n' || *ihp == '#' || *ihp == '\0')
                        break;

                /* Found a token */
                do {
                        ++offset;
                        ++ihp;
                } while (ihp < &image_header[PAGE_SIZE] &&
                         *ihp != ' ' && *ihp != '\t' && 
                         *ihp != '\n' && *ihp != '#' && *ihp != '\0');

                /* Take into account the \0 that will terminate the token */
                ++offset;
        }

        /* If the script gives a null line as the interpreter, we bail */
        if (offset == 0)
                return (ENOEXEC);

        /* It should not be possible for offset to exceed PAGE_SIZE */
        KKASSERT(offset <= PAGE_SIZE);

        /* Check that we aren't too big */
        if (ihp == &image_header[PAGE_SIZE])
                return (ENAMETOOLONG);

        /*
         * The full path name of the original script file must be tagged
         * onto the end, adjust the offset to deal with it.  
         *
         * The original argv0 is being replaced, set 'length' to the number
         * of bytes being removed.  So 'offset' is the number of bytes being
         * added and 'length' is the number of bytes being removed.
         */
        offset += strlen(imgp->args->fname) + 1;        /* add fname */
        length = strlen(imgp->args->begin_argv) + 1;    /* bytes to delete */

        if (offset > imgp->args->space + length)
                return (E2BIG);

        bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
                imgp->args->endp - (imgp->args->begin_argv + length));

        offset -= length;               /* calculate actual adjustment */
        imgp->args->begin_envv += offset;
        imgp->args->endp += offset;
        imgp->args->space -= offset;
        /* decr argc remove old argv[0], incr argc for fname add, net 0 */

        /*
         * Loop through the interpreter name yet again, copying as
         * we go.
         */
        ihp = &image_header[2];
        offset = 0;
        while (ihp < &image_header[PAGE_SIZE]) {
                /* Skip whitespace */
                if (*ihp == ' ' || *ihp == '\t') {
                        ++ihp;
                        continue;
                }

                /* End of line? */
                if (*ihp == '\n' || *ihp == '#' || *ihp == '\0')
                        break;

                /* Found a token, copy it */
                do {
                        imgp->args->begin_argv[offset] = *ihp;
                        ++ihp;
                        ++offset;
                } while (ihp < &image_header[PAGE_SIZE] &&
                         *ihp != ' ' && *ihp != '\t' && 
                         *ihp != '\n' && *ihp != '#' && *ihp != '\0');

                /* And terminate the argument */
                imgp->args->begin_argv[offset] = '\0';
                imgp->args->argc++;
                ++offset;
        }

        /*
         * Finally, add the filename onto the end for the interpreter to
         * use and copy the interpreter's name to imgp->interpreter_name
         * for exec to use.
         */
        error = copystr(imgp->args->fname, imgp->args->buf + offset,
                        imgp->args->space, &length);

        if (error == 0) {
                error = copystr(imgp->args->begin_argv, imgp->interpreter_name,
                                MAXSHELLCMDLEN, &length);
        }
        return (error);
}

/*
 * Tell kern_execve.c about it, with a little help from the linker.
 */
static struct execsw shell_execsw = { exec_shell_imgact, "#!" };
EXEC_SET(shell, shell_execsw);