sys/kern/imgact_shell.c

   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("$FreeBSD$");
  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.  This code should be changed to know how to
  50  * read in the second page, but I'm not doing that just yet...
  51  */
  52 #if MAXSHELLCMDLEN > PAGE_SIZE
  53 #error "MAXSHELLCMDLEN is larger than a single page!"
  54 #endif
  55
  56 /**
  57  * Shell interpreter image activator. An interpreter name beginning at
  58  * imgp->args->begin_argv is the minimal successful exit requirement.
  59  *
  60  * If the given file is a shell-script, then the first line will start
  61  * with the two characters `#!' (aka SHELLMAGIC), followed by the name
  62  * of the shell-interpreter to run, followed by zero or more tokens.
  63  *
  64  * The interpreter is then started up such that it will see:
  65  *    arg[0] -> The name of interpreter as specified after `#!' in the
  66  *              first line of the script.  The interpreter name must
  67  *              not be longer than MAXSHELLCMDLEN bytes.
  68  *    arg[1] -> *If* there are any additional tokens on the first line,
  69  *              then we add a new arg[1], which is a copy of the rest of
  70  *              that line.  The copy starts at the first token after the
  71  *              interpreter name.  We leave it to the interpreter to
  72  *              parse the tokens in that value.
  73  *    arg[x] -> the full pathname of the script.  This will either be
  74  *              arg[2] or arg[1], depending on whether or not tokens
  75  *              were found after the interpreter name.
  76  *  arg[x+1] -> all the arguments that were specified on the original
  77  *              command line.
  78  *
  79  * This processing is described in the execve(2) man page.
  80  */
  81
  82 /*
  83  * HISTORICAL NOTE: From 1993 to mid-2005, FreeBSD parsed out the tokens as
  84  * found on the first line of the script, and setup each token as a separate
  85  * value in arg[].  This extra processing did not match the behavior of other
  86  * OS's, and caused a few subtle problems.  For one, it meant the kernel was
  87  * deciding how those values should be parsed (wrt characters for quoting or
  88  * comments, etc), while the interpreter might have other rules for parsing.
  89  * It also meant the interpreter had no way of knowing which arguments came
  90  * from the first line of the shell script, and which arguments were specified
  91  * by the user on the command line.  That extra processing was dropped in the
  92  * 6.x branch on May 28, 2005 (matching __FreeBSD_version 600029).
  93  */
  94 int
  95 exec_shell_imgact(imgp)
  96         struct image_params *imgp;
  97 {
  98         const char *image_header = imgp->image_header;
  99         const char *ihp, *interpb, *interpe, *maxp, *optb, *opte, *fname;
 100         int error, offset;
 101         size_t length, clength;
 102         struct vattr vattr;
 103         struct sbuf *sname;
 104
 105         /* a shell script? */
 106         if (((const short *) image_header)[0] != SHELLMAGIC)
 107                 return(-1);
 108
 109         /*
 110          * Don't allow a shell script to be the shell for a shell
 111          *      script. :-)
 112          */
 113         if (imgp->interpreted)
 114                 return(ENOEXEC);
 115
 116         imgp->interpreted = 1;
 117
 118         /*
 119          * At this point we have the first page of the file mapped.
 120          * However, we don't know how far into the page the contents are
 121          * valid -- the actual file might be much shorter than the page.
 122          * So find out the file size.
 123          */
 124         error = VOP_GETATTR(imgp->vp, &vattr, imgp->proc->p_ucred);
 125         if (error)
 126                 return (error);
 127
 128         /*
 129          * Copy shell name and arguments from image_header into a string
 130          *      buffer.  Remember that the caller has mapped only the
 131          *      first page of the file into memory.
 132          */
 133         clength = (vattr.va_size > PAGE_SIZE) ? PAGE_SIZE : vattr.va_size;
 134
 135         maxp = &image_header[clength];
 136         ihp = &image_header[2];
 137
 138         /*
 139          * Find the beginning and end of the interpreter_name.  If the
 140          * line does not include any interpreter, or if the name which
 141          * was found is too long, we bail out.
 142          */
 143         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
 144                 ihp++;
 145         interpb = ihp;
 146         while (ihp < maxp && ((*ihp != ' ') && (*ihp != '\t') && (*ihp != '\n')
 147             && (*ihp != '\0')))
 148                 ihp++;
 149         interpe = ihp;
 150         if (interpb == interpe)
 151                 return (ENOEXEC);
 152         if ((interpe - interpb) >= MAXSHELLCMDLEN)
 153                 return (ENAMETOOLONG);
 154
 155         /*
 156          * Find the beginning of the options (if any), and the end-of-line.
 157          * Then trim the trailing blanks off the value.  Note that some
 158          * other operating systems do *not* trim the trailing whitespace...
 159          */
 160         while (ihp < maxp && ((*ihp == ' ') || (*ihp == '\t')))
 161                 ihp++;
 162         optb = ihp;
 163         while (ihp < maxp && ((*ihp != '\n') && (*ihp != '\0')))
 164                 ihp++;
 165         opte = ihp;
 166         while (--ihp > optb && ((*ihp == ' ') || (*ihp == '\t')))
 167                 opte = ihp;
 168
 169         if (imgp->args->fname != NULL) {
 170                 fname = imgp->args->fname;
 171                 sname = NULL;
 172         } else {
 173                 sname = sbuf_new_auto();
 174                 sbuf_printf(sname, "/dev/fd/%d", imgp->args->fd);
 175                 sbuf_finish(sname);
 176                 fname = sbuf_data(sname);
 177         }
 178
 179         /*
 180          * We need to "pop" (remove) the present value of arg[0], and "push"
 181          * either two or three new values in the arg[] list.  To do this,
 182          * we first shift all the other values in the `begin_argv' area to
 183          * provide the exact amount of room for the values added.  Set up
 184          * `offset' as the number of bytes to be added to the `begin_argv'
 185          * area, and 'length' as the number of bytes being removed.
 186          */
 187         offset = interpe - interpb + 1;                 /* interpreter */
 188         if (opte > optb)                                /* options (if any) */
 189                 offset += opte - optb + 1;
 190         offset += strlen(fname) + 1;                    /* fname of script */
 191         length = (imgp->args->argc == 0) ? 0 :
 192             strlen(imgp->args->begin_argv) + 1;         /* bytes to delete */
 193
 194         if (offset - length > imgp->args->stringspace) {
 195                 if (sname != NULL)
 196                         sbuf_delete(sname);
 197                 return (E2BIG);
 198         }
 199
 200         bcopy(imgp->args->begin_argv + length, imgp->args->begin_argv + offset,
 201             imgp->args->endp - (imgp->args->begin_argv + length));
 202
 203         offset -= length;               /* calculate actual adjustment */
 204         imgp->args->begin_envv += offset;
 205         imgp->args->endp += offset;
 206         imgp->args->stringspace -= offset;
 207
 208         /*
 209          * If there was no arg[0] when we started, then the interpreter_name
 210          * is adding an argument (instead of replacing the arg[0] we started
 211          * with).  And we're always adding an argument when we include the
 212          * full pathname of the original script.
 213          */
 214         if (imgp->args->argc == 0)
 215                 imgp->args->argc = 1;
 216         imgp->args->argc++;
 217
 218         /*
 219          * The original arg[] list has been shifted appropriately.  Copy in
 220          * the interpreter name and options-string.
 221          */
 222         length = interpe - interpb;
 223         bcopy(interpb, imgp->args->buf, length);
 224         *(imgp->args->buf + length) = '\0';
 225         offset = length + 1;
 226         if (opte > optb) {
 227                 length = opte - optb;
 228                 bcopy(optb, imgp->args->buf + offset, length);
 229                 *(imgp->args->buf + offset + length) = '\0';
 230                 offset += length + 1;
 231                 imgp->args->argc++;
 232         }
 233
 234         /*
 235          * Finally, add the filename onto the end for the interpreter to
 236          * use and copy the interpreter's name to imgp->interpreter_name
 237          * for exec to use.
 238          */
 239         error = copystr(fname, imgp->args->buf + offset, imgp->args->stringspace,
 240             &length);
 241
 242         if (error == 0)
 243                 error = copystr(imgp->args->begin_argv, imgp->interpreter_name,
 244                     MAXSHELLCMDLEN, &length);
 245
 246         if (sname != NULL)
 247                 sbuf_delete(sname);
 248         return (error);
 249 }
 250
 251 /*
 252  * Tell kern_execve.c about it, with a little help from the linker.
 253  */
 254 static struct execsw shell_execsw = { exec_shell_imgact, "#!" };
 255 EXEC_SET(shell, shell_execsw);