Ejemplo n.º 1
0
Archivo: core.c Proyecto: qmuntada/sh1
void			exec_core(t_lenv *env, char **param)
{
	char		*exec;

	param = check_exec_param(env, param);
	g_bool = 0;
	if (!fork())
	{
		g_bool = 1;
		if (param && param[0][0] == '/' && access(param[0], X_OK) == 0)
			execve(param[0], param, list_to_char(env));
		else if (param && param[0][0] == '.' && param[0][1] == '/' &&
				access(param[0], X_OK) == 0)
			execve(param[0], param, list_to_char(env));
		else if (param && (exec = check_exec(param[0], env)) != NULL)
			execve(exec, param, list_to_char(env));
		else
		{
			ft_putstr(param[0]);
			ft_putstr(": command not found\n");
		}
		exit(0);
	}
	else
		wait(0);
}
Ejemplo n.º 2
0
/* ARGSUSED */
int
sys_execve(struct proc *p, void *v, register_t *retval)
{
	struct sys_execve_args /* {
		syscallarg(const char *) path;
		syscallarg(char *const *) argp;
		syscallarg(char *const *) envp;
	} */ *uap = v;
	int error;
	struct exec_package pack;
	struct nameidata nid;
	struct vattr attr;
	struct ucred *cred = p->p_ucred;
	char *argp;
	char * const *cpp, *dp, *sp;
#ifdef KTRACE
	char *env_start;
#endif
	struct process *pr = p->p_p;
	long argc, envc;
	size_t len, sgap;
#ifdef MACHINE_STACK_GROWS_UP
	size_t slen;
#endif
	char *stack;
	struct ps_strings arginfo;
	struct vmspace *vm = pr->ps_vmspace;
	char **tmpfap;
	extern struct emul emul_native;
#if NSYSTRACE > 0
	int wassugid = ISSET(pr->ps_flags, PS_SUGID | PS_SUGIDEXEC);
	size_t pathbuflen;
#endif
	char *pathbuf = NULL;
	struct vnode *otvp;

	/* get other threads to stop */
	if ((error = single_thread_set(p, SINGLE_UNWIND, 1)))
		return (error);

	/*
	 * Cheap solution to complicated problems.
	 * Mark this process as "leave me alone, I'm execing".
	 */
	atomic_setbits_int(&pr->ps_flags, PS_INEXEC);

#if NSYSTRACE > 0
	if (ISSET(p->p_flag, P_SYSTRACE)) {
		systrace_execve0(p);
		pathbuf = pool_get(&namei_pool, PR_WAITOK);
		error = copyinstr(SCARG(uap, path), pathbuf, MAXPATHLEN,
		    &pathbuflen);
		if (error != 0)
			goto clrflag;
	}
#endif
	if (pathbuf != NULL) {
		NDINIT(&nid, LOOKUP, NOFOLLOW, UIO_SYSSPACE, pathbuf, p);
	} else {
		NDINIT(&nid, LOOKUP, NOFOLLOW, UIO_USERSPACE,
		    SCARG(uap, path), p);
	}

	/*
	 * initialize the fields of the exec package.
	 */
	if (pathbuf != NULL)
		pack.ep_name = pathbuf;
	else
		pack.ep_name = (char *)SCARG(uap, path);
	pack.ep_hdr = malloc(exec_maxhdrsz, M_EXEC, M_WAITOK);
	pack.ep_hdrlen = exec_maxhdrsz;
	pack.ep_hdrvalid = 0;
	pack.ep_ndp = &nid;
	pack.ep_interp = NULL;
	pack.ep_emul_arg = NULL;
	VMCMDSET_INIT(&pack.ep_vmcmds);
	pack.ep_vap = &attr;
	pack.ep_emul = &emul_native;
	pack.ep_flags = 0;

	/* see if we can run it. */
	if ((error = check_exec(p, &pack)) != 0) {
		goto freehdr;
	}

	/* XXX -- THE FOLLOWING SECTION NEEDS MAJOR CLEANUP */

	/* allocate an argument buffer */
	argp = km_alloc(NCARGS, &kv_exec, &kp_pageable, &kd_waitok);
#ifdef DIAGNOSTIC
	if (argp == NULL)
		panic("execve: argp == NULL");
#endif
	dp = argp;
	argc = 0;

	/* copy the fake args list, if there's one, freeing it as we go */
	if (pack.ep_flags & EXEC_HASARGL) {
		tmpfap = pack.ep_fa;
		while (*tmpfap != NULL) {
			char *cp;

			cp = *tmpfap;
			while (*cp)
				*dp++ = *cp++;
			*dp++ = '\0';

			free(*tmpfap, M_EXEC, 0);
			tmpfap++; argc++;
		}
		free(pack.ep_fa, M_EXEC, 0);
		pack.ep_flags &= ~EXEC_HASARGL;
	}

	/* Now get argv & environment */
	if (!(cpp = SCARG(uap, argp))) {
		error = EFAULT;
		goto bad;
	}

	if (pack.ep_flags & EXEC_SKIPARG)
		cpp++;

	while (1) {
		len = argp + ARG_MAX - dp;
		if ((error = copyin(cpp, &sp, sizeof(sp))) != 0)
			goto bad;
		if (!sp)
			break;
		if ((error = copyinstr(sp, dp, len, &len)) != 0) {
			if (error == ENAMETOOLONG)
				error = E2BIG;
			goto bad;
		}
		dp += len;
		cpp++;
		argc++;
	}

	/* must have at least one argument */
	if (argc == 0) {
		error = EINVAL;
		goto bad;
	}

#ifdef KTRACE
	if (KTRPOINT(p, KTR_EXECARGS))
		ktrexec(p, KTR_EXECARGS, argp, dp - argp);
#endif

	envc = 0;
	/* environment does not need to be there */
	if ((cpp = SCARG(uap, envp)) != NULL ) {
#ifdef KTRACE
		env_start = dp;
#endif
		while (1) {
			len = argp + ARG_MAX - dp;
			if ((error = copyin(cpp, &sp, sizeof(sp))) != 0)
				goto bad;
			if (!sp)
				break;
			if ((error = copyinstr(sp, dp, len, &len)) != 0) {
				if (error == ENAMETOOLONG)
					error = E2BIG;
				goto bad;
			}
			dp += len;
			cpp++;
			envc++;
		}

#ifdef KTRACE
		if (KTRPOINT(p, KTR_EXECENV))
			ktrexec(p, KTR_EXECENV, env_start, dp - env_start);
#endif
	}

	dp = (char *)(((long)dp + _STACKALIGNBYTES) & ~_STACKALIGNBYTES);

	sgap = STACKGAPLEN;

	/*
	 * If we have enabled random stackgap, the stack itself has already
	 * been moved from a random location, but is still aligned to a page
	 * boundary.  Provide the lower bits of random placement now.
	 */
	if (stackgap_random != 0) {
		sgap += arc4random() & PAGE_MASK;
		sgap = (sgap + _STACKALIGNBYTES) & ~_STACKALIGNBYTES;
	}

	/* Now check if args & environ fit into new stack */
	len = ((argc + envc + 2 + pack.ep_emul->e_arglen) * sizeof(char *) +
	    sizeof(long) + dp + sgap + sizeof(struct ps_strings)) - argp;

	len = (len + _STACKALIGNBYTES) &~ _STACKALIGNBYTES;

	if (len > pack.ep_ssize) { /* in effect, compare to initial limit */
		error = ENOMEM;
		goto bad;
	}

	/* adjust "active stack depth" for process VSZ */
	pack.ep_ssize = len;	/* maybe should go elsewhere, but... */

	/*
	 * we're committed: any further errors will kill the process, so
	 * kill the other threads now.
	 */
	single_thread_set(p, SINGLE_EXIT, 0);

	/*
	 * Prepare vmspace for remapping. Note that uvmspace_exec can replace
	 * pr_vmspace!
	 */
	uvmspace_exec(p, VM_MIN_ADDRESS, VM_MAXUSER_ADDRESS);

	vm = pr->ps_vmspace;
	/* Now map address space */
	vm->vm_taddr = (char *)trunc_page(pack.ep_taddr);
	vm->vm_tsize = atop(round_page(pack.ep_taddr + pack.ep_tsize) -
	    trunc_page(pack.ep_taddr));
	vm->vm_daddr = (char *)trunc_page(pack.ep_daddr);
	vm->vm_dsize = atop(round_page(pack.ep_daddr + pack.ep_dsize) -
	    trunc_page(pack.ep_daddr));
	vm->vm_dused = 0;
	vm->vm_ssize = atop(round_page(pack.ep_ssize));
	vm->vm_maxsaddr = (char *)pack.ep_maxsaddr;
	vm->vm_minsaddr = (char *)pack.ep_minsaddr;

	/* create the new process's VM space by running the vmcmds */
#ifdef DIAGNOSTIC
	if (pack.ep_vmcmds.evs_used == 0)
		panic("execve: no vmcmds");
#endif
	error = exec_process_vmcmds(p, &pack);

	/* if an error happened, deallocate and punt */
	if (error)
		goto exec_abort;

	/* old "stackgap" is gone now */
	pr->ps_stackgap = 0;

#ifdef MACHINE_STACK_GROWS_UP
	pr->ps_strings = (vaddr_t)vm->vm_maxsaddr + sgap;
        if (uvm_map_protect(&vm->vm_map, (vaddr_t)vm->vm_maxsaddr,
            trunc_page(pr->ps_strings), PROT_NONE, TRUE))
                goto exec_abort;
#else
	pr->ps_strings = (vaddr_t)vm->vm_minsaddr - sizeof(arginfo) - sgap;
        if (uvm_map_protect(&vm->vm_map,
            round_page(pr->ps_strings + sizeof(arginfo)),
            (vaddr_t)vm->vm_minsaddr, PROT_NONE, TRUE))
                goto exec_abort;
#endif

	/* remember information about the process */
	arginfo.ps_nargvstr = argc;
	arginfo.ps_nenvstr = envc;

#ifdef MACHINE_STACK_GROWS_UP
	stack = (char *)vm->vm_maxsaddr + sizeof(arginfo) + sgap;
	slen = len - sizeof(arginfo) - sgap;
#else
	stack = (char *)(vm->vm_minsaddr - len);
#endif
	/* Now copy argc, args & environ to new stack */
	if (!(*pack.ep_emul->e_copyargs)(&pack, &arginfo, stack, argp))
		goto exec_abort;

	/* copy out the process's ps_strings structure */
	if (copyout(&arginfo, (char *)pr->ps_strings, sizeof(arginfo)))
		goto exec_abort;

	stopprofclock(pr);	/* stop profiling */
	fdcloseexec(p);		/* handle close on exec */
	execsigs(p);		/* reset caught signals */
	TCB_SET(p, NULL);	/* reset the TCB address */
	pr->ps_kbind_addr = 0;	/* reset the kbind bits */
	pr->ps_kbind_cookie = 0;

	/* set command name & other accounting info */
	memset(p->p_comm, 0, sizeof(p->p_comm));
	len = min(nid.ni_cnd.cn_namelen, MAXCOMLEN);
	memcpy(p->p_comm, nid.ni_cnd.cn_nameptr, len);
	pr->ps_acflag &= ~AFORK;

	/* record proc's vnode, for use by sysctl */
	otvp = pr->ps_textvp;
	vref(pack.ep_vp);
	pr->ps_textvp = pack.ep_vp;
	if (otvp)
		vrele(otvp);

	atomic_setbits_int(&pr->ps_flags, PS_EXEC);
	if (pr->ps_flags & PS_PPWAIT) {
		atomic_clearbits_int(&pr->ps_flags, PS_PPWAIT);
		atomic_clearbits_int(&pr->ps_pptr->ps_flags, PS_ISPWAIT);
		wakeup(pr->ps_pptr);
	}

	/*
	 * If process does execve() while it has a mismatched real,
	 * effective, or saved uid/gid, we set PS_SUGIDEXEC.
	 */
	if (cred->cr_uid != cred->cr_ruid ||
	    cred->cr_uid != cred->cr_svuid ||
	    cred->cr_gid != cred->cr_rgid ||
	    cred->cr_gid != cred->cr_svgid)
		atomic_setbits_int(&pr->ps_flags, PS_SUGIDEXEC);
	else
		atomic_clearbits_int(&pr->ps_flags, PS_SUGIDEXEC);

	atomic_clearbits_int(&pr->ps_flags, PS_TAMED);
	tame_dropwpaths(pr);

	/*
	 * deal with set[ug]id.
	 * MNT_NOEXEC has already been used to disable s[ug]id.
	 */
	if ((attr.va_mode & (VSUID | VSGID)) && proc_cansugid(p)) {
		int i;

		atomic_setbits_int(&pr->ps_flags, PS_SUGID|PS_SUGIDEXEC);

#ifdef KTRACE
		/*
		 * If process is being ktraced, turn off - unless
		 * root set it.
		 */
		if (pr->ps_tracevp && !(pr->ps_traceflag & KTRFAC_ROOT))
			ktrcleartrace(pr);
#endif
		p->p_ucred = cred = crcopy(cred);
		if (attr.va_mode & VSUID)
			cred->cr_uid = attr.va_uid;
		if (attr.va_mode & VSGID)
			cred->cr_gid = attr.va_gid;

		/*
		 * For set[ug]id processes, a few caveats apply to
		 * stdin, stdout, and stderr.
		 */
		error = 0;
		fdplock(p->p_fd);
		for (i = 0; i < 3; i++) {
			struct file *fp = NULL;

			/*
			 * NOTE - This will never return NULL because of
			 * immature fds. The file descriptor table is not
			 * shared because we're suid.
			 */
			fp = fd_getfile(p->p_fd, i);

			/*
			 * Ensure that stdin, stdout, and stderr are already
			 * allocated.  We do not want userland to accidentally
			 * allocate descriptors in this range which has implied
			 * meaning to libc.
			 */
			if (fp == NULL) {
				short flags = FREAD | (i == 0 ? 0 : FWRITE);
				struct vnode *vp;
				int indx;

				if ((error = falloc(p, &fp, &indx)) != 0)
					break;
#ifdef DIAGNOSTIC
				if (indx != i)
					panic("sys_execve: falloc indx != i");
#endif
				if ((error = cdevvp(getnulldev(), &vp)) != 0) {
					fdremove(p->p_fd, indx);
					closef(fp, p);
					break;
				}
				if ((error = VOP_OPEN(vp, flags, cred, p)) != 0) {
					fdremove(p->p_fd, indx);
					closef(fp, p);
					vrele(vp);
					break;
				}
				if (flags & FWRITE)
					vp->v_writecount++;
				fp->f_flag = flags;
				fp->f_type = DTYPE_VNODE;
				fp->f_ops = &vnops;
				fp->f_data = (caddr_t)vp;
				FILE_SET_MATURE(fp, p);
			}
		}
		fdpunlock(p->p_fd);
		if (error)
			goto exec_abort;
	} else
		atomic_clearbits_int(&pr->ps_flags, PS_SUGID);

	/*
	 * Reset the saved ugids and update the process's copy of the
	 * creds if the creds have been changed
	 */
	if (cred->cr_uid != cred->cr_svuid ||
	    cred->cr_gid != cred->cr_svgid) {
		/* make sure we have unshared ucreds */
		p->p_ucred = cred = crcopy(cred);
		cred->cr_svuid = cred->cr_uid;
		cred->cr_svgid = cred->cr_gid;
	}

	if (pr->ps_ucred != cred) {
		struct ucred *ocred;

		ocred = pr->ps_ucred;
		crhold(cred);
		pr->ps_ucred = cred;
		crfree(ocred);
	}

	if (pr->ps_flags & PS_SUGIDEXEC) {
		int i, s = splclock();

		timeout_del(&pr->ps_realit_to);
		for (i = 0; i < nitems(pr->ps_timer); i++) {
			timerclear(&pr->ps_timer[i].it_interval);
			timerclear(&pr->ps_timer[i].it_value);
		}
		splx(s);
	}

	/* reset CPU time usage for the thread, but not the process */
	timespecclear(&p->p_tu.tu_runtime);
	p->p_tu.tu_uticks = p->p_tu.tu_sticks = p->p_tu.tu_iticks = 0;

	km_free(argp, NCARGS, &kv_exec, &kp_pageable);

	pool_put(&namei_pool, nid.ni_cnd.cn_pnbuf);
	vn_close(pack.ep_vp, FREAD, cred, p);

	/*
	 * notify others that we exec'd
	 */
	KNOTE(&pr->ps_klist, NOTE_EXEC);

	/* setup new registers and do misc. setup. */
	if (pack.ep_emul->e_fixup != NULL) {
		if ((*pack.ep_emul->e_fixup)(p, &pack) != 0)
			goto free_pack_abort;
	}
#ifdef MACHINE_STACK_GROWS_UP
	(*pack.ep_emul->e_setregs)(p, &pack, (u_long)stack + slen, retval);
#else
	(*pack.ep_emul->e_setregs)(p, &pack, (u_long)stack, retval);
#endif

	/* map the process's signal trampoline code */
	if (exec_sigcode_map(pr, pack.ep_emul))
		goto free_pack_abort;

#ifdef __HAVE_EXEC_MD_MAP
	/* perform md specific mappings that process might need */
	if (exec_md_map(p, &pack))
		goto free_pack_abort;
#endif

	if (pr->ps_flags & PS_TRACED)
		psignal(p, SIGTRAP);

	free(pack.ep_hdr, M_EXEC, pack.ep_hdrlen);

	/*
	 * Call emulation specific exec hook. This can setup per-process
	 * p->p_emuldata or do any other per-process stuff an emulation needs.
	 *
	 * If we are executing process of different emulation than the
	 * original forked process, call e_proc_exit() of the old emulation
	 * first, then e_proc_exec() of new emulation. If the emulation is
	 * same, the exec hook code should deallocate any old emulation
	 * resources held previously by this process.
	 */
	if (pr->ps_emul && pr->ps_emul->e_proc_exit &&
	    pr->ps_emul != pack.ep_emul)
		(*pr->ps_emul->e_proc_exit)(p);

	p->p_descfd = 255;
	if ((pack.ep_flags & EXEC_HASFD) && pack.ep_fd < 255)
		p->p_descfd = pack.ep_fd;

	/*
	 * Call exec hook. Emulation code may NOT store reference to anything
	 * from &pack.
	 */
	if (pack.ep_emul->e_proc_exec)
		(*pack.ep_emul->e_proc_exec)(p, &pack);

#if defined(KTRACE) && defined(COMPAT_LINUX)
	/* update ps_emul, but don't ktrace it if native-execing-native */
	if (pr->ps_emul != pack.ep_emul || pack.ep_emul != &emul_native) {
		pr->ps_emul = pack.ep_emul;

		if (KTRPOINT(p, KTR_EMUL))
			ktremul(p);
	}
#else
	/* update ps_emul, the old value is no longer needed */
	pr->ps_emul = pack.ep_emul;
#endif

	atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);
	single_thread_clear(p, P_SUSPSIG);

#if NSYSTRACE > 0
	if (ISSET(p->p_flag, P_SYSTRACE) &&
	    wassugid && !ISSET(pr->ps_flags, PS_SUGID | PS_SUGIDEXEC))
		systrace_execve1(pathbuf, p);
#endif

	if (pathbuf != NULL)
		pool_put(&namei_pool, pathbuf);

	return (0);

bad:
	/* free the vmspace-creation commands, and release their references */
	kill_vmcmds(&pack.ep_vmcmds);
	/* kill any opened file descriptor, if necessary */
	if (pack.ep_flags & EXEC_HASFD) {
		pack.ep_flags &= ~EXEC_HASFD;
		fdplock(p->p_fd);
		(void) fdrelease(p, pack.ep_fd);
		fdpunlock(p->p_fd);
	}
	if (pack.ep_interp != NULL)
		pool_put(&namei_pool, pack.ep_interp);
	if (pack.ep_emul_arg != NULL)
		free(pack.ep_emul_arg, M_TEMP, pack.ep_emul_argsize);
	/* close and put the exec'd file */
	vn_close(pack.ep_vp, FREAD, cred, p);
	pool_put(&namei_pool, nid.ni_cnd.cn_pnbuf);
	km_free(argp, NCARGS, &kv_exec, &kp_pageable);

 freehdr:
	free(pack.ep_hdr, M_EXEC, pack.ep_hdrlen);
#if NSYSTRACE > 0
 clrflag:
#endif
	atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);
	single_thread_clear(p, P_SUSPSIG);

	if (pathbuf != NULL)
		pool_put(&namei_pool, pathbuf);

	return (error);

exec_abort:
	/*
	 * the old process doesn't exist anymore.  exit gracefully.
	 * get rid of the (new) address space we have created, if any, get rid
	 * of our namei data and vnode, and exit noting failure
	 */
	uvm_deallocate(&vm->vm_map, VM_MIN_ADDRESS,
		VM_MAXUSER_ADDRESS - VM_MIN_ADDRESS);
	if (pack.ep_interp != NULL)
		pool_put(&namei_pool, pack.ep_interp);
	if (pack.ep_emul_arg != NULL)
		free(pack.ep_emul_arg, M_TEMP, pack.ep_emul_argsize);
	pool_put(&namei_pool, nid.ni_cnd.cn_pnbuf);
	vn_close(pack.ep_vp, FREAD, cred, p);
	km_free(argp, NCARGS, &kv_exec, &kp_pageable);

free_pack_abort:
	free(pack.ep_hdr, M_EXEC, pack.ep_hdrlen);
	if (pathbuf != NULL)
		pool_put(&namei_pool, pathbuf);
	exit1(p, W_EXITCODE(0, SIGABRT), EXIT_NORMAL);

	/* NOTREACHED */
	atomic_clearbits_int(&pr->ps_flags, PS_INEXEC);

	return (0);
}
Ejemplo n.º 3
0
/*
 * exec_script_makecmds(): Check if it's an executable shell script.
 *
 * Given a proc pointer and an exec package pointer, see if the referent
 * of the epp is in shell script.  If it is, then set things up so that
 * the script can be run.  This involves preparing the address space
 * and arguments for the shell which will run the script.
 *
 * This function is ultimately responsible for creating a set of vmcmds
 * which can be used to build the process's vm space and inserting them
 * into the exec package.
 */
int
exec_script_makecmds(struct proc *p, struct exec_package *epp)
{
    int error, hdrlinelen, shellnamelen, shellarglen;
    char *hdrstr = epp->ep_hdr;
    char *cp, *shellname, *shellarg, *oldpnbuf;
    char **shellargp = NULL, **tmpsap;
    struct vnode *scriptvp;
#ifdef SETUIDSCRIPTS
    uid_t script_uid = -1;
    gid_t script_gid = -1;
    u_short script_sbits;
#endif

    /*
     * remember the old vp and pnbuf for later, so we can restore
     * them if check_exec() fails.
     */
    scriptvp = epp->ep_vp;
    oldpnbuf = epp->ep_ndp->ni_cnd.cn_pnbuf;

    /*
     * if the magic isn't that of a shell script, or we've already
     * done shell script processing for this exec, punt on it.
     */
    if ((epp->ep_flags & EXEC_INDIR) != 0 ||
            epp->ep_hdrvalid < EXEC_SCRIPT_MAGICLEN ||
            strncmp(hdrstr, EXEC_SCRIPT_MAGIC, EXEC_SCRIPT_MAGICLEN))
        return ENOEXEC;

    /*
     * check that the shell spec is terminated by a newline,
     * and that it isn't too large.  Don't modify the
     * buffer unless we're ready to commit to handling it.
     * (The latter requirement means that we have to check
     * for both spaces and tabs later on.)
     */
    hdrlinelen = min(epp->ep_hdrvalid, MAXINTERP);
    for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; cp < hdrstr + hdrlinelen;
            cp++) {
        if (*cp == '\n') {
            *cp = '\0';
            break;
        }
    }
    if (cp >= hdrstr + hdrlinelen)
        return ENOEXEC;

    shellname = NULL;
    shellarg = NULL;
    shellarglen = 0;

    /* strip spaces before the shell name */
    for (cp = hdrstr + EXEC_SCRIPT_MAGICLEN; *cp == ' ' || *cp == '\t';
            cp++)
        ;

    /* collect the shell name; remember its length for later */
    shellname = cp;
    shellnamelen = 0;
    if (*cp == '\0')
        goto check_shell;
    for ( /* cp = cp */ ; *cp != '\0' && *cp != ' ' && *cp != '\t'; cp++)
        shellnamelen++;
    if (*cp == '\0')
        goto check_shell;
    *cp++ = '\0';

    /* skip spaces before any argument */
    for ( /* cp = cp */ ; *cp == ' ' || *cp == '\t'; cp++)
        ;
    if (*cp == '\0')
        goto check_shell;

    /*
     * collect the shell argument.  everything after the shell name
     * is passed as ONE argument; that's the correct (historical)
     * behaviour.
     */
    shellarg = cp;
    for ( /* cp = cp */ ; *cp != '\0'; cp++)
        shellarglen++;
    *cp++ = '\0';

check_shell:
#ifdef SETUIDSCRIPTS
    /*
     * MNT_NOSUID and STRC are already taken care of by check_exec,
     * so we don't need to worry about them now or later.
     */
    script_sbits = epp->ep_vap->va_mode & (VSUID | VSGID);
    if (script_sbits != 0) {
        script_uid = epp->ep_vap->va_uid;
        script_gid = epp->ep_vap->va_gid;
    }
#endif
#ifdef FDSCRIPTS
    /*
     * if the script isn't readable, or it's set-id, then we've
     * gotta supply a "/dev/fd/..." for the shell to read.
     * Note that stupid shells (csh) do the wrong thing, and
     * close all open fd's when they start.  That kills this
     * method of implementing "safe" set-id and x-only scripts.
     */
    vn_lock(scriptvp, LK_EXCLUSIVE|LK_RETRY, p);
    error = VOP_ACCESS(scriptvp, VREAD, p->p_ucred, p);
    VOP_UNLOCK(scriptvp, 0, p);
    if (error == EACCES
#ifdef SETUIDSCRIPTS
            || script_sbits
#endif
       ) {
        struct file *fp;

#ifdef DIAGNOSTIC
        if (epp->ep_flags & EXEC_HASFD)
            panic("exec_script_makecmds: epp already has a fd");
#endif

        if ((error = falloc(p, &fp, &epp->ep_fd)))
            goto fail;

        epp->ep_flags |= EXEC_HASFD;
        fp->f_type = DTYPE_VNODE;
        fp->f_ops = &vnops;
        fp->f_data = (caddr_t) scriptvp;
        fp->f_flag = FREAD;
        FILE_SET_MATURE(fp);
    }
#endif

    /* set up the parameters for the recursive check_exec() call */
    epp->ep_ndp->ni_dirp = shellname;
    epp->ep_ndp->ni_segflg = UIO_SYSSPACE;
    epp->ep_flags |= EXEC_INDIR;

    /* and set up the fake args list, for later */
    MALLOC(shellargp, char **, 4 * sizeof(char *), M_EXEC, M_WAITOK);
    tmpsap = shellargp;
    *tmpsap = malloc(shellnamelen + 1, M_EXEC, M_WAITOK);
    strlcpy(*tmpsap++, shellname, shellnamelen + 1);
    if (shellarg != NULL) {
        *tmpsap = malloc(shellarglen + 1, M_EXEC, M_WAITOK);
        strlcpy(*tmpsap++, shellarg, shellarglen + 1);
    }
    *tmpsap = malloc(MAXPATHLEN, M_EXEC, M_WAITOK);
#ifdef FDSCRIPTS
    if ((epp->ep_flags & EXEC_HASFD) == 0) {
#endif
        /* normally can't fail, but check for it if diagnostic */
#if NSYSTRACE > 0
        if (ISSET(p->p_flag, P_SYSTRACE)) {
            error = systrace_scriptname(p, *tmpsap);
            if (error == 0)
                tmpsap++;
            else
                /*
                 * Since systrace_scriptname() provides a
                 * convenience, not a security issue, we are
                 * safe to do this.
                 */
                error = copystr(epp->ep_name, *tmpsap++,
                                MAXPATHLEN, NULL);
        } else
            error = copyinstr(epp->ep_name, *tmpsap++, MAXPATHLEN,
                              NULL);
#else
        error = copyinstr(epp->ep_name, *tmpsap++, MAXPATHLEN,
                          (size_t *)0);
#endif
#ifdef DIAGNOSTIC
        if (error != 0)
            panic("exec_script: copyinstr couldn't fail");
#endif
#ifdef FDSCRIPTS
    } else
        snprintf(*tmpsap++, MAXPATHLEN, "/dev/fd/%d", epp->ep_fd);
#endif
    *tmpsap = NULL;

    /*
     * mark the header we have as invalid; check_exec will read
     * the header from the new executable
     */
    epp->ep_hdrvalid = 0;

    if ((error = check_exec(p, epp)) == 0) {
        /* note that we've clobbered the header */
        epp->ep_flags |= EXEC_DESTR;

        /*
         * It succeeded.  Unlock the script and
         * close it if we aren't using it any more.
         * Also, set things up so that the fake args
         * list will be used.
         */
        if ((epp->ep_flags & EXEC_HASFD) == 0)
            vn_close(scriptvp, FREAD, p->p_ucred, p);

        /* free the old pathname buffer */
        pool_put(&namei_pool, oldpnbuf);

        epp->ep_flags |= (EXEC_HASARGL | EXEC_SKIPARG);
        epp->ep_fa = shellargp;
#ifdef SETUIDSCRIPTS
        /*
         * set things up so that set-id scripts will be
         * handled appropriately
         */
        epp->ep_vap->va_mode |= script_sbits;
        if (script_sbits & VSUID)
            epp->ep_vap->va_uid = script_uid;
        if (script_sbits & VSGID)
            epp->ep_vap->va_gid = script_gid;
#endif
        return (0);
    }

    /* XXX oldpnbuf not set for "goto fail" path */
    epp->ep_ndp->ni_cnd.cn_pnbuf = oldpnbuf;
#ifdef FDSCRIPTS
fail:
#endif
    /* note that we've clobbered the header */
    epp->ep_flags |= EXEC_DESTR;

    /* kill the opened file descriptor, else close the file */
    if (epp->ep_flags & EXEC_HASFD) {
        epp->ep_flags &= ~EXEC_HASFD;
        (void) fdrelease(p, epp->ep_fd);
    } else
        vn_close(scriptvp, FREAD, p->p_ucred, p);

    pool_put(&namei_pool, epp->ep_ndp->ni_cnd.cn_pnbuf);

    /* free the fake arg list, because we're not returning it */
    if ((tmpsap = shellargp) != NULL) {
        while (*tmpsap != NULL) {
            free(*tmpsap, M_EXEC);
            tmpsap++;
        }
        FREE(shellargp, M_EXEC);
    }

    /*
     * free any vmspace-creation commands,
     * and release their references
     */
    kill_vmcmds(&epp->ep_vmcmds);

    return error;
}