1 /* $NetBSD: exec_script.c,v 1.75 2018/04/27 18:33:24 christos 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 1.75 2018/04/27 18:33:24 christos Exp $"); 35 36 #if defined(SETUIDSCRIPTS) && !defined(FDSCRIPTS) 37 #define FDSCRIPTS /* Need this for safe set-id scripts. */ 38 #endif 39 40 #include <sys/param.h> 41 #include <sys/systm.h> 42 #include <sys/proc.h> 43 #include <sys/kmem.h> 44 #include <sys/vnode.h> 45 #include <sys/namei.h> 46 #include <sys/file.h> 47 #ifdef SETUIDSCRIPTS 48 #include <sys/stat.h> 49 #endif 50 #include <sys/filedesc.h> 51 #include <sys/exec.h> 52 #include <sys/resourcevar.h> 53 #include <sys/module.h> 54 #include <sys/exec_script.h> 55 #include <sys/exec_elf.h> 56 57 MODULE(MODULE_CLASS_EXEC, exec_script, NULL); 58 59 static struct execsw exec_script_execsw = { 60 .es_hdrsz = SCRIPT_HDR_SIZE, 61 .es_makecmds = exec_script_makecmds, 62 .u = { 63 .elf_probe_func = NULL, 64 }, 65 .es_emul = NULL, 66 .es_prio = EXECSW_PRIO_ANY, 67 .es_arglen = 0, 68 .es_copyargs = NULL, 69 .es_setregs = NULL, 70 .es_coredump = NULL, 71 .es_setup_stack = exec_setup_stack, 72 }; 73 74 static int 75 exec_script_modcmd(modcmd_t cmd, void *arg) 76 { 77 78 switch (cmd) { 79 case MODULE_CMD_INIT: 80 return exec_add(&exec_script_execsw, 1); 81 82 case MODULE_CMD_FINI: 83 return exec_remove(&exec_script_execsw, 1); 84 85 case MODULE_CMD_AUTOUNLOAD: 86 /* 87 * We don't want to be autounloaded because our use is 88 * transient: no executables with p_execsw equal to 89 * exec_script_execsw will exist, so FINI will never 90 * return EBUSY. However, the system will run scripts 91 * often. Return EBUSY here to prevent this module from 92 * ping-ponging in and out of the kernel. 93 */ 94 return EBUSY; 95 96 default: 97 return ENOTTY; 98 } 99 } 100 101 /* 102 * exec_script_makecmds(): Check if it's an executable shell script. 103 * 104 * Given a proc pointer and an exec package pointer, see if the referent 105 * of the epp is in shell script. If it is, then set thing up so that 106 * the script can be run. This involves preparing the address space 107 * and arguments for the shell which will run the script. 108 * 109 * This function is ultimately responsible for creating a set of vmcmds 110 * which can be used to build the process's vm space and inserting them 111 * into the exec package. 112 */ 113 int 114 exec_script_makecmds(struct lwp *l, struct exec_package *epp) 115 { 116 int error, hdrlinelen, shellnamelen, shellarglen; 117 char *hdrstr = epp->ep_hdr; 118 char *cp, *shellname, *shellarg; 119 size_t shellargp_len; 120 struct exec_fakearg *shellargp; 121 struct exec_fakearg *tmpsap; 122 struct pathbuf *shell_pathbuf; 123 struct vnode *scriptvp; 124 #ifdef SETUIDSCRIPTS 125 /* Gcc needs those initialized for spurious uninitialized warning */ 126 uid_t script_uid = (uid_t) -1; 127 gid_t script_gid = NOGROUP; 128 u_short script_sbits; 129 #endif 130 131 /* 132 * if the magic isn't that of a shell script, or we've already 133 * done shell script processing for this exec, punt on it. 134 */ 135 if ((epp->ep_flags & EXEC_INDIR) != 0 || 136 epp->ep_hdrvalid < EXEC_SCRIPT_MAGICLEN || 137 strncmp(hdrstr, EXEC_SCRIPT_MAGIC, EXEC_SCRIPT_MAGICLEN)) 138 return ENOEXEC; 139 140 /* 141 * Check that the shell spec is terminated by a newline, and that 142 * it isn't too large. 143 */ 144 hdrlinelen = min(epp->ep_hdrvalid, SCRIPT_HDR_SIZE); 145 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; cp < hdrstr + hdrlinelen; 146 cp++) { 147 if (*cp == '\n') { 148 *cp = '\0'; 149 break; 150 } 151 } 152 if (cp >= hdrstr + hdrlinelen) 153 return ENOEXEC; 154 155 /* strip spaces before the shell name */ 156 for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; *cp == ' ' || *cp == '\t'; 157 cp++) 158 ; 159 if (*cp == '\0') 160 return ENOEXEC; 161 162 shellarg = NULL; 163 shellarglen = 0; 164 165 /* collect the shell name; remember its length for later */ 166 shellname = cp; 167 shellnamelen = 0; 168 for ( /* cp = cp */ ; *cp != '\0' && *cp != ' ' && *cp != '\t'; cp++) 169 shellnamelen++; 170 if (*cp == '\0') 171 goto check_shell; 172 *cp++ = '\0'; 173 174 /* skip spaces before any argument */ 175 for ( /* cp = cp */ ; *cp == ' ' || *cp == '\t'; cp++) 176 ; 177 if (*cp == '\0') 178 goto check_shell; 179 180 /* 181 * collect the shell argument. everything after the shell name 182 * is passed as ONE argument; that's the correct (historical) 183 * behaviour. 184 */ 185 shellarg = cp; 186 for ( /* cp = cp */ ; *cp != '\0'; cp++) 187 shellarglen++; 188 *cp++ = '\0'; 189 190 check_shell: 191 #ifdef SETUIDSCRIPTS 192 /* 193 * MNT_NOSUID has already taken care of by check_exec, 194 * so we don't need to worry about it now or later. We 195 * will need to check PSL_TRACED later, however. 196 */ 197 script_sbits = epp->ep_vap->va_mode & (S_ISUID | S_ISGID); 198 if (script_sbits != 0) { 199 script_uid = epp->ep_vap->va_uid; 200 script_gid = epp->ep_vap->va_gid; 201 } 202 #endif 203 #ifdef FDSCRIPTS 204 /* 205 * if the script isn't readable, or it's set-id, then we've 206 * gotta supply a "/dev/fd/..." for the shell to read. 207 * Note that stupid shells (csh) do the wrong thing, and 208 * close all open fd's when the start. That kills this 209 * method of implementing "safe" set-id and x-only scripts. 210 */ 211 vn_lock(epp->ep_vp, LK_EXCLUSIVE | LK_RETRY); 212 error = VOP_ACCESS(epp->ep_vp, VREAD, l->l_cred); 213 VOP_UNLOCK(epp->ep_vp); 214 if (error == EACCES 215 #ifdef SETUIDSCRIPTS 216 || script_sbits 217 #endif 218 ) { 219 struct file *fp; 220 221 KASSERT(!(epp->ep_flags & EXEC_HASFD)); 222 223 if ((error = fd_allocfile(&fp, &epp->ep_fd)) != 0) { 224 scriptvp = NULL; 225 shellargp = NULL; 226 goto fail; 227 } 228 epp->ep_flags |= EXEC_HASFD; 229 fp->f_type = DTYPE_VNODE; 230 fp->f_ops = &vnops; 231 fp->f_vnode = epp->ep_vp; 232 fp->f_flag = FREAD; 233 fd_affix(curproc, fp, epp->ep_fd); 234 } 235 #endif 236 237 /* set up the fake args list */ 238 shellargp_len = 4 * sizeof(*shellargp); 239 shellargp = kmem_alloc(shellargp_len, KM_SLEEP); 240 tmpsap = shellargp; 241 tmpsap->fa_len = shellnamelen + 1; 242 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP); 243 strlcpy(tmpsap->fa_arg, shellname, tmpsap->fa_len); 244 tmpsap++; 245 if (shellarg != NULL) { 246 tmpsap->fa_len = shellarglen + 1; 247 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP); 248 strlcpy(tmpsap->fa_arg, shellarg, tmpsap->fa_len); 249 tmpsap++; 250 } 251 tmpsap->fa_len = MAXPATHLEN; 252 tmpsap->fa_arg = kmem_alloc(tmpsap->fa_len, KM_SLEEP); 253 #ifdef FDSCRIPTS 254 if ((epp->ep_flags & EXEC_HASFD) == 0) { 255 #endif 256 /* normally can't fail, but check for it if diagnostic */ 257 error = copystr(epp->ep_kname, tmpsap->fa_arg, MAXPATHLEN, 258 NULL); 259 KASSERT(error == 0); 260 tmpsap++; 261 #ifdef FDSCRIPTS 262 } else { 263 snprintf(tmpsap->fa_arg, MAXPATHLEN, "/dev/fd/%d", epp->ep_fd); 264 tmpsap++; 265 } 266 #endif 267 tmpsap->fa_arg = NULL; 268 269 /* Save the old vnode so we can clean it up later. */ 270 scriptvp = epp->ep_vp; 271 epp->ep_vp = NULL; 272 273 /* Note that we're trying recursively. */ 274 epp->ep_flags |= EXEC_INDIR; 275 276 /* 277 * mark the header we have as invalid; check_exec will read 278 * the header from the new executable 279 */ 280 epp->ep_hdrvalid = 0; 281 282 /* try loading the interpreter */ 283 if ((error = exec_makepathbuf(l, shellname, UIO_SYSSPACE, 284 &shell_pathbuf, NULL)) == 0) { 285 error = check_exec(l, epp, shell_pathbuf); 286 pathbuf_destroy(shell_pathbuf); 287 } 288 289 /* note that we've clobbered the header */ 290 epp->ep_flags |= EXEC_DESTR; 291 292 if (error == 0) { 293 /* 294 * It succeeded. Unlock the script and 295 * close it if we aren't using it any more. 296 * Also, set things up so that the fake args 297 * list will be used. 298 */ 299 if ((epp->ep_flags & EXEC_HASFD) == 0) { 300 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY); 301 VOP_CLOSE(scriptvp, FREAD, l->l_cred); 302 vput(scriptvp); 303 } 304 305 epp->ep_flags |= (EXEC_HASARGL | EXEC_SKIPARG); 306 epp->ep_fa = shellargp; 307 epp->ep_fa_len = shellargp_len; 308 #ifdef SETUIDSCRIPTS 309 /* 310 * set thing up so that set-id scripts will be 311 * handled appropriately. PSL_TRACED will be 312 * checked later when the shell is actually 313 * exec'd. 314 */ 315 epp->ep_vap->va_mode |= script_sbits; 316 if (script_sbits & S_ISUID) 317 epp->ep_vap->va_uid = script_uid; 318 if (script_sbits & S_ISGID) 319 epp->ep_vap->va_gid = script_gid; 320 #endif 321 return (0); 322 } 323 324 #ifdef FDSCRIPTS 325 fail: 326 #endif 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 fd_close(epp->ep_fd); 332 } else if (scriptvp) { 333 vn_lock(scriptvp, LK_EXCLUSIVE | LK_RETRY); 334 VOP_CLOSE(scriptvp, FREAD, l->l_cred); 335 vput(scriptvp); 336 } 337 338 /* free the fake arg list, because we're not returning it */ 339 if ((tmpsap = shellargp) != NULL) { 340 while (tmpsap->fa_arg != NULL) { 341 kmem_free(tmpsap->fa_arg, tmpsap->fa_len); 342 tmpsap++; 343 } 344 kmem_free(shellargp, shellargp_len); 345 } 346 347 /* 348 * free any vmspace-creation commands, 349 * and release their references 350 */ 351 kill_vmcmds(&epp->ep_vmcmds); 352 353 return error; 354 } 355