The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/imgact_shell.c

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    1 /*-
    2  * Copyright (c) 1993, David Greenman
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: stable/10/sys/kern/imgact_shell.c 325514 2017-11-07 14:28:10Z pfg $");
   29 
   30 #include <sys/param.h>
   31 #include <sys/vnode.h>
   32 #include <sys/proc.h>
   33 #include <sys/sbuf.h>
   34 #include <sys/systm.h>
   35 #include <sys/sysproto.h>
   36 #include <sys/exec.h>
   37 #include <sys/imgact.h>
   38 #include <sys/kernel.h>
   39 
   40 #if BYTE_ORDER == LITTLE_ENDIAN
   41 #define SHELLMAGIC      0x2123 /* #! */
   42 #else
   43 #define SHELLMAGIC      0x2321
   44 #endif
   45 
   46 /*
   47  * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE.  This is
   48  * significant because the caller has only mapped in one page of the
   49  * file we're reading.
   50  */
   51 #if MAXSHELLCMDLEN > PAGE_SIZE
   52 #error "MAXSHELLCMDLEN is larger than a single page!"
   53 #endif
   54 
   55 /*
   56  * MAXSHELLCMDLEN must be at least MAXINTERP plus the size of the `#!'
   57  * prefix and terminating newline.
   58  */
   59 CTASSERT(MAXSHELLCMDLEN >= MAXINTERP + 3);
   60 
   61 /**
   62  * Shell interpreter image activator. An interpreter name beginning at
   63  * imgp->args->begin_argv is the minimal successful exit requirement.
   64  *
   65  * If the given file is a shell-script, then the first line will start
   66  * with the two characters `#!' (aka SHELLMAGIC), followed by the name
   67  * of the shell-interpreter to run, followed by zero or more tokens.
   68  *
   69  * The interpreter is then started up such that it will see:
   70  *    arg[0] -> The name of interpreter as specified after `#!' in the
   71  *              first line of the script.  The interpreter name must
   72  *              not be longer than MAXSHELLCMDLEN bytes.
   73  *    arg[1] -> *If* there are any additional tokens on the first line,
   74  *              then we add a new arg[1], which is a copy of the rest of
   75  *              that line.  The copy starts at the first token after the
   76  *              interpreter name.  We leave it to the interpreter to
   77  *              parse the tokens in that value.
   78  *    arg[x] -> the full pathname of the script.  This will either be
   79  *              arg[2] or arg[1], depending on whether or not tokens
   80  *              were found after the interpreter name.
   81  *  arg[x+1] -> all the arguments that were specified on the original
   82  *              command line.
   83  *
   84  * This processing is described in the execve(2) man page.
   85  */
   86 
   87 /*
   88  * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
   89  * found on the first line of the script, and setup each token as a separate
   90  * value in arg[].  This extra processing did not match the behavior of other
   91  * OS's, and caused a few subtle problems.  For one, it meant the kernel was
   92  * deciding how those values should be parsed (wrt characters for quoting or
   93  * comments, etc), while the interpreter might have other rules for parsing.
   94  * It also meant the interpreter had no way of knowing which arguments came
   95  * from the first line of the shell script, and which arguments were specified
   96  * by the user on the command line.  That extra processing was dropped in the
   97  * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
   98  */
   99 int
  100 exec_shell_imgact(struct image_params *imgp)
  101 {
  102         const char *image_header = imgp->image_header;
  103         const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
  104         int error, offset;
  105         size_t length;
  106         struct vattr vattr;
  107         struct sbuf *sname;
  108 
  109         /* a shell script? */
  110         if (((const short *)image_header)[0] != SHELLMAGIC)
  111                 return (-1);
  112 
  113         /*
  114          * Don't allow a shell script to be the shell for a shell
  115          *      script. :-)
  116          */
  117         if (imgp->interpreted & IMGACT_SHELL)
  118                 return (ENOEXEC);
  119 
  120         imgp->interpreted |= IMGACT_SHELL;
  121 
  122         /*
  123          * At this point we have the first page of the file mapped.
  124          * However, we don't know how far into the page the contents are
  125          * valid -- the actual file might be much shorter than the page.
  126          * So find out the file size.
  127          */
  128         error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
  129         if (error)
  130                 return (error);
  131 
  132         /*
  133          * Copy shell name and arguments from image_header into a string
  134          * buffer.
  135          */
  136         maxp = &image_header[MIN(vattr.va_size, MAXSHELLCMDLEN)];
  137         ihp = &image_header[2];
  138 
  139         /*
  140          * Find the beginning and end of the interpreter_name.  If the
  141          * line does not include any interpreter, or if the name which
  142          * was found is too long, we bail out.
  143          */
  144         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  145                 ihp++;
  146         interpb = ihp;
  147         while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
  148             && (*ihp != '\0')))
  149                 ihp++;
  150         interpe = ihp;
  151         if (interpb == interpe)
  152                 return (ENOEXEC);
  153         if (interpe - interpb >= MAXINTERP)
  154                 return (ENAMETOOLONG);
  155 
  156         /*
  157          * Find the beginning of the options (if any), and the end-of-line.
  158          * Then trim the trailing blanks off the value.  Note that some
  159          * other operating systems do *not* trim the trailing whitespace...
  160          */
  161         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  162                 ihp++;
  163         optb = ihp;
  164         while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
  165                 ihp++;
  166         opte = ihp;
  167         if (opte == maxp)
  168                 return (ENOEXEC);
  169         while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
  170                 opte = ihp;
  171 
  172         if (imgp->args->fname != NULL) {
  173                 fname = imgp->args->fname;
  174                 sname = NULL;
  175         } else {
  176                 sname = sbuf_new_auto();
  177                 sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
  178                 sbuf_finish(sname);
  179                 fname = sbuf_data(sname);
  180         }
  181 
  182         /*
  183          * We need to "pop" (remove) the present value of arg[0], and "push"
  184          * either two or three new values in the arg[] list.  To do this,
  185          * we first shift all the other values in the `begin_argv' area to
  186          * provide the exact amount of room for the values added.  Set up
  187          * `offset' as the number of bytes to be added to the `begin_argv'
  188          * area, and 'length' as the number of bytes being removed.
  189          */
  190         offset = interpe - interpb + 1;                 /* interpreter */
  191         if (opte > optb)                                /* options (if any) */
  192                 offset += opte - optb + 1;
  193         offset += strlen(fname) + 1;                    /* fname of script */
  194         length = (imgp->args->argc == 0) ? 0 :
  195             strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
  196 
  197         if (offset > imgp->args->stringspace + length) {
  198                 if (sname != NULL)
  199                         sbuf_delete(sname);
  200                 return (E2BIG);
  201         }
  202 
  203         bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
  204             imgp->args->endp - (imgp->args->begin_argv + length));
  205 
  206         offset -= length;               /* calculate actual adjustment */
  207         imgp->args->begin_envv += offset;
  208         imgp->args->endp += offset;
  209         imgp->args->stringspace -= offset;
  210 
  211         /*
  212          * If there was no arg[0] when we started, then the interpreter_name
  213          * is adding an argument (instead of replacing the arg[0] we started
  214          * with).  And we're always adding an argument when we include the
  215          * full pathname of the original script.
  216          */
  217         if (imgp->args->argc == 0)
  218                 imgp->args->argc = 1;
  219         imgp->args->argc++;
  220 
  221         /*
  222          * The original arg[] list has been shifted appropriately.  Copy in
  223          * the interpreter name and options-string.
  224          */
  225         length = interpe - interpb;
  226         bcopy(interpb, imgp->args->begin_argv, length);
  227         *(imgp->args->begin_argv + length) = '\0';
  228         offset = length + 1;
  229         if (opte > optb) {
  230                 length = opte - optb;
  231                 bcopy(optb, imgp->args->begin_argv + offset, length);
  232                 *(imgp->args->begin_argv + offset + length) = '\0';
  233                 offset += length + 1;
  234                 imgp->args->argc++;
  235         }
  236 
  237         /*
  238          * Finally, add the filename onto the end for the interpreter to
  239          * use and copy the interpreter's name to imgp->interpreter_name
  240          * for exec to use.
  241          */
  242         error = copystr(fname, imgp->args->begin_argv + offset,
  243             imgp->args->stringspace, NULL);
  244 
  245         if (error == 0)
  246                 imgp->interpreter_name = imgp->args->begin_argv;
  247 
  248         if (sname != NULL)
  249                 sbuf_delete(sname);
  250         return (error);
  251 }
  252 
  253 /*
  254  * Tell kern_execve.c about it, with a little help from the linker.
  255  */
  256 static struct execsw shell_execsw = { exec_shell_imgact, "#!" };
  257 EXEC_SET(shell, shell_execsw);

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