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  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 1993, David Greenman
    5  * All rights reserved.
    6  *
    7  * Redistribution and use in source and binary forms, with or without
    8  * modification, are permitted provided that the following conditions
    9  * are met:
   10  * 1. Redistributions of source code must retain the above copyright
   11  *    notice, this list of conditions and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  */
   28 
   29 #include <sys/cdefs.h>
   30 __FBSDID("$FreeBSD: stable/12/sys/kern/imgact_shell.c 330842 2018-03-13 13:09:10Z emaste $");
   31 
   32 #include <sys/param.h>
   33 #include <sys/vnode.h>
   34 #include <sys/proc.h>
   35 #include <sys/sbuf.h>
   36 #include <sys/systm.h>
   37 #include <sys/sysproto.h>
   38 #include <sys/exec.h>
   39 #include <sys/imgact.h>
   40 #include <sys/kernel.h>
   41 
   42 #if BYTE_ORDER == LITTLE_ENDIAN
   43 #define SHELLMAGIC      0x2123 /* #! */
   44 #else
   45 #define SHELLMAGIC      0x2321
   46 #endif
   47 
   48 /*
   49  * At the time of this writing, MAXSHELLCMDLEN == PAGE_SIZE.  This is
   50  * significant because the caller has only mapped in one page of the
   51  * file we're reading.
   52  */
   53 #if MAXSHELLCMDLEN > PAGE_SIZE
   54 #error "MAXSHELLCMDLEN is larger than a single page!"
   55 #endif
   56 
   57 /*
   58  * MAXSHELLCMDLEN must be at least MAXINTERP plus the size of the `#!'
   59  * prefix and terminating newline.
   60  */
   61 CTASSERT(MAXSHELLCMDLEN >= MAXINTERP + 3);
   62 
   63 /**
   64  * Shell interpreter image activator. An interpreter name beginning at
   65  * imgp->args->begin_argv is the minimal successful exit requirement.
   66  *
   67  * If the given file is a shell-script, then the first line will start
   68  * with the two characters `#!' (aka SHELLMAGIC), followed by the name
   69  * of the shell-interpreter to run, followed by zero or more tokens.
   70  *
   71  * The interpreter is then started up such that it will see:
   72  *    arg[0] -> The name of interpreter as specified after `#!' in the
   73  *              first line of the script.  The interpreter name must
   74  *              not be longer than MAXSHELLCMDLEN bytes.
   75  *    arg[1] -> *If* there are any additional tokens on the first line,
   76  *              then we add a new arg[1], which is a copy of the rest of
   77  *              that line.  The copy starts at the first token after the
   78  *              interpreter name.  We leave it to the interpreter to
   79  *              parse the tokens in that value.
   80  *    arg[x] -> the full pathname of the script.  This will either be
   81  *              arg[2] or arg[1], depending on whether or not tokens
   82  *              were found after the interpreter name.
   83  *  arg[x+1] -> all the arguments that were specified on the original
   84  *              command line.
   85  *
   86  * This processing is described in the execve(2) man page.
   87  */
   88 
   89 /*
   90  * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
   91  * found on the first line of the script, and setup each token as a separate
   92  * value in arg[].  This extra processing did not match the behavior of other
   93  * OS's, and caused a few subtle problems.  For one, it meant the kernel was
   94  * deciding how those values should be parsed (wrt characters for quoting or
   95  * comments, etc), while the interpreter might have other rules for parsing.
   96  * It also meant the interpreter had no way of knowing which arguments came
   97  * from the first line of the shell script, and which arguments were specified
   98  * by the user on the command line.  That extra processing was dropped in the
   99  * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
  100  */
  101 int
  102 exec_shell_imgact(struct image_params *imgp)
  103 {
  104         const char *image_header = imgp->image_header;
  105         const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
  106         int error, offset;
  107         size_t length;
  108         struct vattr vattr;
  109         struct sbuf *sname;
  110 
  111         /* a shell script? */
  112         if (((const short *)image_header)[0] != SHELLMAGIC)
  113                 return (-1);
  114 
  115         /*
  116          * Don't allow a shell script to be the shell for a shell
  117          *      script. :-)
  118          */
  119         if (imgp->interpreted & IMGACT_SHELL)
  120                 return (ENOEXEC);
  121 
  122         imgp->interpreted |= IMGACT_SHELL;
  123 
  124         /*
  125          * At this point we have the first page of the file mapped.
  126          * However, we don't know how far into the page the contents are
  127          * valid -- the actual file might be much shorter than the page.
  128          * So find out the file size.
  129          */
  130         error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
  131         if (error)
  132                 return (error);
  133 
  134         /*
  135          * Copy shell name and arguments from image_header into a string
  136          * buffer.
  137          */
  138         maxp = &image_header[MIN(vattr.va_size, MAXSHELLCMDLEN)];
  139         ihp = &image_header[2];
  140 
  141         /*
  142          * Find the beginning and end of the interpreter_name.  If the
  143          * line does not include any interpreter, or if the name which
  144          * was found is too long, we bail out.
  145          */
  146         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  147                 ihp++;
  148         interpb = ihp;
  149         while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
  150             && (*ihp != '\0')))
  151                 ihp++;
  152         interpe = ihp;
  153         if (interpb == interpe)
  154                 return (ENOEXEC);
  155         if (interpe - interpb >= MAXINTERP)
  156                 return (ENAMETOOLONG);
  157 
  158         /*
  159          * Find the beginning of the options (if any), and the end-of-line.
  160          * Then trim the trailing blanks off the value.  Note that some
  161          * other operating systems do *not* trim the trailing whitespace...
  162          */
  163         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
  164                 ihp++;
  165         optb = ihp;
  166         while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
  167                 ihp++;
  168         opte = ihp;
  169         if (opte == maxp)
  170                 return (ENOEXEC);
  171         while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
  172                 opte = ihp;
  173 
  174         if (imgp->args->fname != NULL) {
  175                 fname = imgp->args->fname;
  176                 sname = NULL;
  177         } else {
  178                 sname = sbuf_new_auto();
  179                 sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
  180                 sbuf_finish(sname);
  181                 fname = sbuf_data(sname);
  182         }
  183 
  184         /*
  185          * We need to "pop" (remove) the present value of arg[0], and "push"
  186          * either two or three new values in the arg[] list.  To do this,
  187          * we first shift all the other values in the `begin_argv' area to
  188          * provide the exact amount of room for the values added.  Set up
  189          * `offset' as the number of bytes to be added to the `begin_argv'
  190          * area, and 'length' as the number of bytes being removed.
  191          */
  192         offset = interpe - interpb + 1;                 /* interpreter */
  193         if (opte > optb)                                /* options (if any) */
  194                 offset += opte - optb + 1;
  195         offset += strlen(fname) + 1;                    /* fname of script */
  196         length = (imgp->args->argc == 0) ? 0 :
  197             strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
  198 
  199         if (offset > imgp->args->stringspace + length) {
  200                 if (sname != NULL)
  201                         sbuf_delete(sname);
  202                 return (E2BIG);
  203         }
  204 
  205         bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
  206             imgp->args->endp - (imgp->args->begin_argv + length));
  207 
  208         offset -= length;               /* calculate actual adjustment */
  209         imgp->args->begin_envv += offset;
  210         imgp->args->endp += offset;
  211         imgp->args->stringspace -= offset;
  212 
  213         /*
  214          * If there was no arg[0] when we started, then the interpreter_name
  215          * is adding an argument (instead of replacing the arg[0] we started
  216          * with).  And we're always adding an argument when we include the
  217          * full pathname of the original script.
  218          */
  219         if (imgp->args->argc == 0)
  220                 imgp->args->argc = 1;
  221         imgp->args->argc++;
  222 
  223         /*
  224          * The original arg[] list has been shifted appropriately.  Copy in
  225          * the interpreter name and options-string.
  226          */
  227         length = interpe - interpb;
  228         bcopy(interpb, imgp->args->begin_argv, length);
  229         *(imgp->args->begin_argv + length) = '\0';
  230         offset = length + 1;
  231         if (opte > optb) {
  232                 length = opte - optb;
  233                 bcopy(optb, imgp->args->begin_argv + offset, length);
  234                 *(imgp->args->begin_argv + offset + length) = '\0';
  235                 offset += length + 1;
  236                 imgp->args->argc++;
  237         }
  238 
  239         /*
  240          * Finally, add the filename onto the end for the interpreter to
  241          * use and copy the interpreter's name to imgp->interpreter_name
  242          * for exec to use.
  243          */
  244         error = copystr(fname, imgp->args->begin_argv + offset,
  245             imgp->args->stringspace, NULL);
  246 
  247         if (error == 0)
  248                 imgp->interpreter_name = imgp->args->begin_argv;
  249 
  250         if (sname != NULL)
  251                 sbuf_delete(sname);
  252         return (error);
  253 }
  254 
  255 /*
  256  * Tell kern_execve.c about it, with a little help from the linker.
  257  */
  258 static struct execsw shell_execsw = {
  259         .ex_imgact = exec_shell_imgact,
  260         .ex_name = "#!"
  261 };
  262 EXEC_SET(shell, shell_execsw);

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