imgact_shell.c revision 210475
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: head/sys/kern/imgact_shell.c 210475 2010-07-25 17:43:38Z alc $"); 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 */ 94int 95exec_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->begin_argv, length); 224 *(imgp->args->begin_argv + length) = '\0'; 225 offset = length + 1; 226 if (opte > optb) { 227 length = opte - optb; 228 bcopy(optb, imgp->args->begin_argv + offset, length); 229 *(imgp->args->begin_argv + 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->begin_argv + offset, 240 imgp->args->stringspace, NULL); 241 242 if (error == 0) 243 error = copystr(imgp->args->begin_argv, imgp->interpreter_name, 244 MAXSHELLCMDLEN, NULL); 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 */ 254static struct execsw shell_execsw = { exec_shell_imgact, "#!" }; 255EXEC_SET(shell, shell_execsw); 256