imgact_shell.c

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/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * 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.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include <sys/param.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/systm.h>
#include <sys/sysproto.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
 
/*
 * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE.  This is
 * significant because the caller has only mapped in one page of the
 * file we're reading.
 */
#if MAXSHELLCMDLEN > PAGE_SIZE
#error "MAXSHELLCMDLEN is larger than a single page!"
#endif
 
/*
 * MAXSHELLCMDLEN must be at least MAXINTERP plus the size of the `#!'
 * prefix and terminating newline.
 */
CTASSERT(MAXSHELLCMDLEN >= MAXINTERP + 3);
 
/*
 * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
 * found on the first line of the script, and setup each token as a separate
 * value in arg[].  This extra processing did not match the behavior of other
 * OS's, and caused a few subtle problems.  For one, it meant the kernel was
 * deciding how those values should be parsed (wrt characters for quoting or
 * comments, etc), while the interpreter might have other rules for parsing.
 * It also meant the interpreter had no way of knowing which arguments came
 * from the first line of the shell script, and which arguments were specified
 * by the user on the command line.  That extra processing was dropped in the
 * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
 */
int
exec_shell_imgact(struct image_params *imgp)
{
        const char *image_header = imgp->image_header;
        const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
        int error, offset;
        size_t length;
        struct vattr vattr;
        struct sbuf *sname;
 
        /* 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 & IMGACT_SHELL)
                return (ENOEXEC);
 
        imgp->interpreted |= IMGACT_SHELL;
 
        /*
         * At this point we have the first page of the file mapped.
         * However, we don't know how far into the page the contents are
         * valid -- the actual file might be much shorter than the page.
         * So find out the file size.
         */
        error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
        if (error)
                return (error);
 
        /*
         * Copy shell name and arguments from image_header into a string
         * buffer.
         */
        maxp = &image_header[MIN(vattr.va_size, MAXSHELLCMDLEN)];
        ihp = &image_header[2];
 
        /*
         * Find the beginning and end of the interpreter_name.  If the
         * line does not include any interpreter, or if the name which
         * was found is too long, we bail out.
         */
        while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
                ihp++;
        interpb = ihp;
        while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
            && (*ihp != '\0')))
                ihp++;
        interpe = ihp;
        if (interpb == interpe)
                return (ENOEXEC);
        if (interpe - interpb >= MAXINTERP)
                return (ENAMETOOLONG);
 
        /*
         * Find the beginning of the options (if any), and the end-of-line.
         * Then trim the trailing blanks off the value.  Note that some
         * other operating systems do *not* trim the trailing whitespace...
         */
        while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
                ihp++;
        optb = ihp;
        while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
                ihp++;
        opte = ihp;
        if (opte == maxp)
                return (ENOEXEC);
        while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
                opte = ihp;
 
        if (imgp->args->fname != NULL) {
                fname = imgp->args->fname;
                sname = NULL;
        } else {
                sname = sbuf_new_auto();
                sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
                sbuf_finish(sname);
                fname = sbuf_data(sname);
        }
 
        /*
         * We need to "pop" (remove) the present value of arg[0], and "push"
         * either two or three new values in the arg[] list.  To do this,
         * we first shift all the other values in the `begin_argv' area to
         * provide the exact amount of room for the values added.  Set up
         * `offset' as the number of bytes to be added to the `begin_argv'
         * area, and 'length' as the number of bytes being removed.
         */
        offset = interpe - interpb + 1;                 /* interpreter */
        if (opte > optb)                                /* options (if any) */
                offset += opte - optb + 1;
        offset += strlen(fname) + 1;                    /* fname of script */
        length = (imgp->args->argc == 0) ? 0 :
            strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
 
        error = exec_args_adjust_args(imgp->args, length, offset);
        if (error != 0) {
                if (sname != NULL)
                        sbuf_delete(sname);
                return (error);
        }
 
        /*
         * If there was no arg[0] when we started, then the interpreter_name
         * is adding an argument (instead of replacing the arg[0] we started
         * with).  And we're always adding an argument when we include the
         * full pathname of the original script.
         */
        if (imgp->args->argc == 0)
                imgp->args->argc = 1;
        imgp->args->argc++;
 
        /*
         * The original arg[] list has been shifted appropriately.  Copy in
         * the interpreter name and options-string.
         */
        length = interpe - interpb;
        bcopy(interpb, imgp->args->begin_argv, length);
        *(imgp->args->begin_argv + length) = '\0';
        offset = length + 1;
        if (opte > optb) {
                length = opte - optb;
                bcopy(optb, imgp->args->begin_argv + offset, length);
                *(imgp->args->begin_argv + offset + length) = '\0';
                offset += length + 1;
                imgp->args->argc++;
        }
 
        /*
         * 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(fname, imgp->args->begin_argv + offset,
            imgp->args->stringspace, NULL);
 
        if (error == 0)
                imgp->interpreter_name = imgp->args->begin_argv;
 
        if (sname != NULL)
                sbuf_delete(sname);
        return (error);
}
 
/*
 * Tell kern_execve.c about it, with a little help from the linker.
 */
static struct execsw shell_execsw = {
        .ex_imgact = exec_shell_imgact,
        .ex_name = "#!"
};
EXEC_SET(shell, shell_execsw);