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: releng/6.4/sys/kern/imgact_shell.c 147479 2005-06-19 02:21:03Z gad $");
   29 
   30 #include <sys/param.h>
   31 #include <sys/vnode.h>
   32 #include <sys/proc.h>
   33 #include <sys/systm.h>
   34 #include <sys/sysproto.h>
   35 #include <sys/exec.h>
   36 #include <sys/imgact.h>
   37 #include <sys/kernel.h>
   38 
   39 #if BYTE_ORDER == LITTLE_ENDIAN
   40 #define SHELLMAGIC      0x2123 /* #! */
   41 #else
   42 #define SHELLMAGIC      0x2321
   43 #endif
   44 
   45 /*
   46  * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE.  This is
   47  * significant because the caller has only mapped in one page of the
   48  * file we're reading.  This code should be changed to know how to
   49  * read in the second page, but I'm not doing that just yet...
   50  */
   51 #if MAXSHELLCMDLEN > PAGE_SIZE
   52 #error "MAXSHELLCMDLEN is larger than a single page!"
   53 #endif
   54 
   55 /**
   56  * Shell interpreter image activator. An interpreter name beginning at
   57  * imgp->args->begin_argv is the minimal successful exit requirement.
   58  *
   59  * If the given file is a shell-script, then the first line will start
   60  * with the two characters `#!' (aka SHELLMAGIC), followed by the name
   61  * of the shell-interpreter to run, followed by zero or more tokens.
   62  *
   63  * The interpreter is then started up such that it will see:
   64  *    arg[0] -> The name of interpreter as specified after `#!' in the
   65  *              first line of the script.  The interpreter name must
   66  *              not be longer than MAXSHELLCMDLEN bytes.
   67  *    arg[1] -> *If* there are any additional tokens on the first line,
   68  *              then we add a new arg[1], which is a copy of the rest of
   69  *              that line.  The copy starts at the first token after the
   70  *              interpreter name.  We leave it to the interpreter to
   71  *              parse the tokens in that value.
   72  *    arg[x] -> the full pathname of the script.  This will either be
   73  *              arg[2] or arg[1], depending on whether or not tokens
   74  *              were found after the interpreter name.
   75  *  arg[x+1] -> all the arguments that were specified on the original
   76  *              command line.
   77  *
   78  * This processing is described in the execve(2) man page.
   79  */
   80 
   81 /*
   82  * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
   83  * found on the first line of the script, and setup each token as a separate
   84  * value in arg[].  This extra processing did not match the behavior of other
   85  * OS's, and caused a few subtle problems.  For one, it meant the kernel was
   86  * deciding how those values should be parsed (wrt characters for quoting or
   87  * comments, etc), while the interpreter might have other rules for parsing.
   88  * It also meant the interpreter had no way of knowing which arguments came
   89  * from the first line of the shell script, and which arguments were specified
   90  * by the user on the command line.  That extra processing was dropped in the
   91  * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
   92  */
   93 int
   94 exec_shell_imgact(imgp)
   95         struct image_params *imgp;
   96 {
   97         const char *image_header = imgp->image_header;
   98         const char *ihp, *interpb, *interpe, *maxp, *optb, *opte;
   99         int error, offset;
  100         size_t length, clength;
  101         struct vattr vattr;
  102 
  103         /* a shell script? */
  104         if (((const short *) image_header)[0] != SHELLMAGIC)
  105                 return(-1);
  106 
  107         /*
  108          * Don't allow a shell script to be the shell for a shell
  109          *      script. :-)
  110          */
  111         if (imgp->interpreted)
  112                 return(ENOEXEC);
  113 
  114         imgp->interpreted = 1;
  115 
  116         /*
  117          * At this point we have the first page of the file mapped.
  118          * However, we don't know how far into the page the contents are
  119          * valid -- the actual file might be much shorter than the page.
  120          * So find out the file size.
  121          */
  122         error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred, curthread);
  123         if (error)
  124                 return (error);
  125 
  126         /*
  127          * Copy shell name and arguments from image_header into a string
  128          *      buffer.  Remember that the caller has mapped only the
  129          *      first page of the file into memory.
  130          */
  131         clength = (vattr.va_size > PAGE_SIZE) ? PAGE_SIZE : vattr.va_size;
  132 
  133         maxp = &image_header[clength];
  134         ihp = &image_header[2];
  135 
  136         /*
  137          * Find the beginning and end of the interpreter_name.  If the
  138          * line does not include any interpreter, or if the name which
  139          * was found is too long, we bail out.
  140          */
  141         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  142                 ihp++;
  143         interpb = ihp;
  144         while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
  145             && (*ihp != '\0')))
  146                 ihp++;
  147         interpe = ihp;
  148         if (interpb == interpe)
  149                 return (ENOEXEC);
  150         if ((interpe - interpb) >= MAXSHELLCMDLEN)
  151                 return (ENAMETOOLONG);
  152 
  153         /*
  154          * Find the beginning of the options (if any), and the end-of-line.
  155          * Then trim the trailing blanks off the value.  Note that some
  156          * other operating systems do *not* trim the trailing whitespace...
  157          */
  158         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  159                 ihp++;
  160         optb = ihp;
  161         while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
  162                 ihp++;
  163         opte = ihp;
  164         while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
  165                 opte = ihp;
  166 
  167         /*
  168          * We need to "pop" (remove) the present value of arg[0], and "push"
  169          * either two or three new values in the arg[] list.  To do this,
  170          * we first shift all the other values in the `begin_argv' area to
  171          * provide the exact amount of room for the values added.  Set up
  172          * `offset' as the number of bytes to be added to the `begin_argv'
  173          * area, and 'length' as the number of bytes being removed.
  174          */
  175         offset = interpe - interpb + 1;                 /* interpreter */
  176         if (opte > optb)                                /* options (if any) */
  177                 offset += opte - optb + 1;
  178         offset += strlen(imgp->args->fname) + 1;        /* fname of script */
  179         length = (imgp->args->argc == 0) ? 0 :
  180             strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
  181 
  182         if (offset - length > imgp->args->stringspace)
  183                 return (E2BIG);
  184 
  185         bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
  186             imgp->args->endp - (imgp->args->begin_argv + length));
  187 
  188         offset -= length;               /* calculate actual adjustment */
  189         imgp->args->begin_envv += offset;
  190         imgp->args->endp += offset;
  191         imgp->args->stringspace -= offset;
  192 
  193         /*
  194          * If there was no arg[0] when we started, then the interpreter_name
  195          * is adding an argument (instead of replacing the arg[0] we started
  196          * with).  And we're always adding an argument when we include the
  197          * full pathname of the original script.
  198          */
  199         if (imgp->args->argc == 0)
  200                 imgp->args->argc = 1;
  201         imgp->args->argc++;
  202 
  203         /*
  204          * The original arg[] list has been shifted appropriately.  Copy in
  205          * the interpreter name and options-string.
  206          */
  207         length = interpe - interpb;
  208         bcopy(interpb, imgp->args->buf, length);
  209         *(imgp->args->buf + length) = '\0';
  210         offset = length + 1;
  211         if (opte > optb) {
  212                 length = opte - optb;
  213                 bcopy(optb, imgp->args->buf + offset, length);
  214                 *(imgp->args->buf + offset + length) = '\0';
  215                 offset += length + 1;
  216                 imgp->args->argc++;
  217         }
  218 
  219         /*
  220          * Finally, add the filename onto the end for the interpreter to
  221          * use and copy the interpreter's name to imgp->interpreter_name
  222          * for exec to use.
  223          */
  224         error = copystr(imgp->args->fname, imgp->args->buf + offset,
  225             imgp->args->stringspace, &length);
  226 
  227         if (error == 0)
  228                 error = copystr(imgp->args->begin_argv, imgp->interpreter_name,
  229                     MAXSHELLCMDLEN, &length);
  230 
  231         return (error);
  232 }
  233 
  234 /*
  235  * Tell kern_execve.c about it, with a little help from the linker.
  236  */
  237 static struct execsw shell_execsw = { exec_shell_imgact, "#!" };
  238 EXEC_SET(shell, shell_execsw);

Cache object: dd5a1677572becd482365a714e739949


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