1 /* $NetBSD: exec_script.c,v 1.52 2006/07/26 09:33:57 dogcow Exp $ */ 2 3 /* 4 * Copyright (c) 1993, 1994, 1996 Christopher G. Demetriou 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 * 3. All advertising materials mentioning features or use of this software 16 * must display the following acknowledgement: 17 * This product includes software developed by Christopher G. Demetriou. 18 * 4. The name of the author may not be used to endorse or promote products 19 * derived from this software without specific prior written permission 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __KERNEL_RCSID(0, "$NetBSD: exec_script.c,v 1.52 2006/07/26 09:33:57 dogcow Exp $"); 35 36 #if defined(SETUIDSCRIPTS) && !defined(FDSCRIPTS) 37 #define FDSCRIPTS /* Need this for safe set-id scripts. */ 38 #endif 39 40 #include "veriexec.h" 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/proc.h> 45 #include <sys/malloc.h> 46 #include <sys/vnode.h> 47 #include <sys/namei.h> 48 #include <sys/file.h> 49 #ifdef SETUIDSCRIPTS 50 #include <sys/stat.h> 51 #endif 52 #include <sys/filedesc.h> 53 #include <sys/exec.h> 54 #include <sys/resourcevar.h> 55 56 #include <sys/exec_script.h> 57 #include <sys/exec_elf.h> 58 59 #if NVERIEXEC > 0 60 #include <sys/verified_exec.h> 61 #endif /* NVERIEXEC > 0 */ 62 63 #ifdef SYSTRACE 64 #include <sys/systrace.h> 65 #endif /* SYSTRACE */ 66 67 /* 68 * exec_script_makecmds(): Check if it's an executable shell script. 69 * 70 * Given a proc pointer and an exec package pointer, see if the referent 71 * of the epp is in shell script. If it is, then set thing up so that 72 * the script can be run. This involves preparing the address space 73 * and arguments for the shell which will run the script. 74 * 75 * This function is ultimately responsible for creating a set of vmcmds 76 * which can be used to build the process's vm space and inserting them 77 * into the exec package. 78 */ 79 int 80 exec_script_makecmds(struct lwp *l, struct exec_package *epp) 81 { 82 int error, hdrlinelen, shellnamelen, shellarglen; 83 char *hdrstr = epp->ep_hdr; 84 char *cp, *shellname, *shellarg, *oldpnbuf; 85 char **shellargp, **tmpsap; 86 struct vnode *scriptvp; 87 #ifdef SETUIDSCRIPTS 88 /* Gcc needs those initialized for spurious uninitialized warning */ 89 uid_t script_uid = (uid_t) -1; 90 gid_t script_gid = NOGROUP; 91 u_short script_sbits; 92 #endif 93 94 /* 95 * if the magic isn't that of a shell script, or we've already 96 * done shell script processing for this exec, punt on it. 97 */ 98 if ((epp->ep_flags & EXEC_INDIR) != 0 || 99 epp->ep_hdrvalid < EXEC_SCRIPT_MAGICLEN || 100 strncmp(hdrstr, EXEC_SCRIPT_MAGIC, EXEC_SCRIPT_MAGICLEN)) 101 return ENOEXEC; 102 103 /* 104 * check that the shell spec is terminated by a newline, 105 * and that it isn't too large. Don't modify the 106 * buffer unless we're ready to commit to handling it. 107 * (The latter requirement means that we have to check 108 * for both spaces and tabs later on.) 109 */ 110 hdrlinelen = min(epp->ep_hdrvalid, SCRIPT_HDR_SIZE); 111 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; cp < hdrstr + hdrlinelen; 112 cp++) { 113 if (*cp == '\n') { 114 *cp = '\0'; 115 break; 116 } 117 } 118 if (cp >= hdrstr + hdrlinelen) 119 return ENOEXEC; 120 121 /* 122 * If the script has an ELF header, don't exec it. 123 */ 124 if (epp->ep_hdrvalid >= sizeof(ELFMAG)-1 && 125 memcmp(hdrstr, ELFMAG, sizeof(ELFMAG)-1) == 0) 126 return ENOEXEC; 127 128 shellname = NULL; 129 shellarg = NULL; 130 shellarglen = 0; 131 132 /* strip spaces before the shell name */ 133 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; *cp == ' ' || *cp == '\t'; 134 cp++) 135 ; 136 137 /* collect the shell name; remember it's length for later */ 138 shellname = cp; 139 shellnamelen = 0; 140 if (*cp == '\0') 141 goto check_shell; 142 for ( /* cp = cp */ ; *cp != '\0' && *cp != ' ' && *cp != '\t'; cp++) 143 shellnamelen++; 144 if (*cp == '\0') 145 goto check_shell; 146 *cp++ = '\0'; 147 148 /* skip spaces before any argument */ 149 for ( /* cp = cp */ ; *cp == ' ' || *cp == '\t'; cp++) 150 ; 151 if (*cp == '\0') 152 goto check_shell; 153 154 /* 155 * collect the shell argument. everything after the shell name 156 * is passed as ONE argument; that's the correct (historical) 157 * behaviour. 158 */ 159 shellarg = cp; 160 for ( /* cp = cp */ ; *cp != '\0'; cp++) 161 shellarglen++; 162 *cp++ = '\0'; 163 164 check_shell: 165 #ifdef SETUIDSCRIPTS 166 /* 167 * MNT_NOSUID has already taken care of by check_exec, 168 * so we don't need to worry about it now or later. We 169 * will need to check P_TRACED later, however. 170 */ 171 script_sbits = epp->ep_vap->va_mode & (S_ISUID | S_ISGID); 172 if (script_sbits != 0) { 173 script_uid = epp->ep_vap->va_uid; 174 script_gid = epp->ep_vap->va_gid; 175 } 176 #endif 177 #ifdef FDSCRIPTS 178 /* 179 * if the script isn't readable, or it's set-id, then we've 180 * gotta supply a "/dev/fd/..." for the shell to read. 181 * Note that stupid shells (csh) do the wrong thing, and 182 * close all open fd's when the start. That kills this 183 * method of implementing "safe" set-id and x-only scripts. 184 */ 185 vn_lock(epp->ep_vp, LK_EXCLUSIVE | LK_RETRY); 186 error = VOP_ACCESS(epp->ep_vp, VREAD, l->l_cred, l); 187 VOP_UNLOCK(epp->ep_vp, 0); 188 if (error == EACCES 189 #ifdef SETUIDSCRIPTS 190 || script_sbits 191 #endif 192 ) { 193 struct file *fp; 194 195 #if defined(DIAGNOSTIC) && defined(FDSCRIPTS) 196 if (epp->ep_flags & EXEC_HASFD) 197 panic("exec_script_makecmds: epp already has a fd"); 198 #endif 199 200 /* falloc() will use the descriptor for us */ 201 if ((error = falloc(l, &fp, &epp->ep_fd)) != 0) { 202 scriptvp = NULL; 203 shellargp = NULL; 204 goto fail; 205 } 206 207 epp->ep_flags |= EXEC_HASFD; 208 fp->f_type = DTYPE_VNODE; 209 fp->f_ops = &vnops; 210 fp->f_data = (caddr_t) epp->ep_vp; 211 fp->f_flag = FREAD; 212 FILE_SET_MATURE(fp); 213 FILE_UNUSE(fp, l); 214 } 215 #endif 216 217 /* set up the parameters for the recursive check_exec() call */ 218 epp->ep_ndp->ni_dirp = shellname; 219 epp->ep_ndp->ni_segflg = UIO_SYSSPACE; 220 epp->ep_flags |= EXEC_INDIR; 221 222 /* and set up the fake args list, for later */ 223 MALLOC(shellargp, char **, 4 * sizeof(char *), M_EXEC, M_WAITOK); 224 tmpsap = shellargp; 225 *tmpsap = malloc(shellnamelen + 1, M_EXEC, M_WAITOK); 226 strlcpy(*tmpsap++, shellname, shellnamelen + 1); 227 if (shellarg != NULL) { 228 *tmpsap = malloc(shellarglen + 1, M_EXEC, M_WAITOK); 229 strlcpy(*tmpsap++, shellarg, shellarglen + 1); 230 } 231 MALLOC(*tmpsap, char *, MAXPATHLEN, M_EXEC, M_WAITOK); 232 #ifdef FDSCRIPTS 233 if ((epp->ep_flags & EXEC_HASFD) == 0) { 234 #endif 235 /* normally can't fail, but check for it if diagnostic */ 236 #ifdef SYSTRACE 237 error = 1; 238 if (ISSET(l->l_proc->p_flag, P_SYSTRACE)) { 239 error = systrace_scriptname(p, *tmpsap); 240 if (error == 0) 241 tmpsap++; 242 } 243 if (error) { 244 /* 245 * Since systrace_scriptname() provides a 246 * convenience, not a security issue, we are 247 * safe to do this. 248 */ 249 error = copystr(epp->ep_name, *tmpsap++, MAXPATHLEN, 250 NULL); 251 } 252 #else 253 error = copyinstr(epp->ep_name, *tmpsap++, MAXPATHLEN, 254 (size_t *)0); 255 #endif /* SYSTRACE */ 256 #ifdef DIAGNOSTIC 257 if (error != 0) 258 panic("exec_script: copyinstr couldn't fail"); 259 #endif 260 #ifdef FDSCRIPTS 261 } else 262 snprintf(*tmpsap++, MAXPATHLEN, "/dev/fd/%d", epp->ep_fd); 263 #endif 264 *tmpsap = NULL; 265 266 /* 267 * mark the header we have as invalid; check_exec will read 268 * the header from the new executable 269 */ 270 epp->ep_hdrvalid = 0; 271 272 /* 273 * remember the old vp and pnbuf for later, so we can restore 274 * them if check_exec() fails. 275 */ 276 scriptvp = epp->ep_vp; 277 oldpnbuf = epp->ep_ndp->ni_cnd.cn_pnbuf; 278 279 #if NVERIEXEC > 0 280 if ((error = check_exec(l, epp, VERIEXEC_INDIRECT)) == 0) { 281 #else 282 if ((error = check_exec(l, epp, 0)) == 0) { 283 #endif /* NVERIEXEC > 0 */ 284 /* note that we've clobbered the header */ 285 epp->ep_flags |= EXEC_DESTR|EXEC_HASES; 286 287 /* 288 * It succeeded. Unlock the script and 289 * close it if we aren't using it any more. 290 * Also, set things up so that the fake args 291 * list will be used. 292 */ 293 if ((epp->ep_flags & EXEC_HASFD) == 0) { 294 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY); 295 VOP_CLOSE(scriptvp, FREAD, l->l_cred, l); 296 vput(scriptvp); 297 } 298 299 /* free the old pathname buffer */ 300 PNBUF_PUT(oldpnbuf); 301 302 epp->ep_flags |= (EXEC_HASARGL | EXEC_SKIPARG); 303 epp->ep_fa = shellargp; 304 #ifdef SETUIDSCRIPTS 305 /* 306 * set thing up so that set-id scripts will be 307 * handled appropriately. P_TRACED will be 308 * checked later when the shell is actually 309 * exec'd. 310 */ 311 epp->ep_vap->va_mode |= script_sbits; 312 if (script_sbits & S_ISUID) 313 epp->ep_vap->va_uid = script_uid; 314 if (script_sbits & S_ISGID) 315 epp->ep_vap->va_gid = script_gid; 316 #endif 317 return (0); 318 } 319 320 /* XXX oldpnbuf not set for "goto fail" path */ 321 epp->ep_ndp->ni_cnd.cn_pnbuf = oldpnbuf; 322 #ifdef FDSCRIPTS 323 fail: 324 #endif 325 /* note that we've clobbered the header */ 326 epp->ep_flags |= EXEC_DESTR; 327 328 /* kill the opened file descriptor, else close the file */ 329 if (epp->ep_flags & EXEC_HASFD) { 330 epp->ep_flags &= ~EXEC_HASFD; 331 (void) fdrelease(l, epp->ep_fd); 332 } else if (scriptvp) { 333 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY); 334 VOP_CLOSE(scriptvp, FREAD, l->l_cred, l); 335 vput(scriptvp); 336 } 337 338 PNBUF_PUT(epp->ep_ndp->ni_cnd.cn_pnbuf); 339 340 /* free the fake arg list, because we're not returning it */ 341 if ((tmpsap = shellargp) != NULL) { 342 while (*tmpsap != NULL) { 343 FREE(*tmpsap, M_EXEC); 344 tmpsap++; 345 } 346 FREE(shellargp, M_EXEC); 347 } 348 349 /* 350 * free any vmspace-creation commands, 351 * and release their references 352 */ 353 kill_vmcmds(&epp->ep_vmcmds); 354 355 return error; 356 } 357