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NetBSD/lib/libutil/login_cap.c
mjf d4a648c345 Implement a new magic string for magic symlinks, @ruid, which exapnds to the 
real user id of the process and use this magic string for per-user tmp.
This should fix PR/35687

Kernel parts reviewed by wrstuden@
2007-12-04 22:09:01 +00:00

988 lines
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/* $NetBSD: login_cap.c,v 1.29 2007/12/04 22:09:02 mjf Exp $ */
/*-
* Copyright (c) 1995,1997 Berkeley Software Design, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Berkeley Software Design,
* Inc.
* 4. The name of Berkeley Software Design, Inc. may not be used to endorse
* or promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN, INC. ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN, INC. BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* BSDI login_cap.c,v 2.13 1998/02/07 03:17:05 prb Exp
*/
#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: login_cap.c,v 1.29 2007/12/04 22:09:02 mjf Exp $");
#endif /* LIBC_SCCS and not lint */
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <sys/param.h>
#include <assert.h>
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <login_cap.h>
#include <paths.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <unistd.h>
#include <util.h>
static u_quad_t multiply(u_quad_t, u_quad_t);
static u_quad_t strtolimit(const char *, char **, int);
static u_quad_t strtosize(const char *, char **, int);
static int gsetrl(login_cap_t *, int, const char *, int type);
static int isinfinite(const char *);
static int envset(void *, const char *, const char *, int);
login_cap_t *
login_getclass(const char *class)
{
const char *classfiles[2];
login_cap_t *lc;
int res;
/* class may be NULL */
if (secure_path(_PATH_LOGIN_CONF) == 0) {
classfiles[0] = _PATH_LOGIN_CONF;
classfiles[1] = NULL;
} else {
classfiles[0] = NULL;
}
if ((lc = malloc(sizeof(login_cap_t))) == NULL) {
syslog(LOG_ERR, "%s:%d malloc: %m", __FILE__, __LINE__);
return (0);
}
lc->lc_cap = 0;
lc->lc_style = 0;
if (class == NULL || class[0] == '\0')
class = LOGIN_DEFCLASS;
if ((lc->lc_class = strdup(class)) == NULL) {
syslog(LOG_ERR, "%s:%d strdup: %m", __FILE__, __LINE__);
free(lc);
return (0);
}
/*
* Not having a login.conf file is not an error condition.
* The individual routines deal reasonably with missing
* capabilities and use default values.
*/
if (classfiles[0] == NULL)
return(lc);
if ((res = cgetent(&lc->lc_cap, classfiles, lc->lc_class)) != 0) {
lc->lc_cap = 0;
switch (res) {
case 1:
syslog(LOG_ERR, "%s: couldn't resolve 'tc'",
lc->lc_class);
break;
case -1:
if (strcmp(lc->lc_class, LOGIN_DEFCLASS) == 0)
return (lc);
syslog(LOG_ERR, "%s: unknown class", lc->lc_class);
break;
case -2:
syslog(LOG_ERR, "%s: getting class information: %m",
lc->lc_class);
break;
case -3:
syslog(LOG_ERR, "%s: 'tc' reference loop",
lc->lc_class);
break;
default:
syslog(LOG_ERR, "%s: unexpected cgetent error",
lc->lc_class);
break;
}
free(lc->lc_class);
free(lc);
return (0);
}
return (lc);
}
login_cap_t *
login_getpwclass(const struct passwd *pwd)
{
/* pwd may be NULL */
return login_getclass(pwd ? pwd->pw_class : NULL);
}
char *
login_getcapstr(login_cap_t *lc, const char *cap, char *def, char *e)
{
char *res = NULL;
int status;
errno = 0;
_DIAGASSERT(cap != NULL);
if (!lc || !lc->lc_cap)
return (def);
switch (status = cgetstr(lc->lc_cap, cap, &res)) {
case -1:
if (res)
free(res);
return (def);
case -2:
syslog(LOG_ERR, "%s: getting capability %s: %m",
lc->lc_class, cap);
if (res)
free(res);
return (e);
default:
if (status >= 0)
return (res);
syslog(LOG_ERR, "%s: unexpected error with capability %s",
lc->lc_class, cap);
if (res)
free(res);
return (e);
}
}
quad_t
login_getcaptime(login_cap_t *lc, const char *cap, quad_t def, quad_t e)
{
char *ep;
char *res = NULL, *sres;
int status;
quad_t q, r;
_DIAGASSERT(cap != NULL);
errno = 0;
if (!lc || !lc->lc_cap)
return (def);
switch (status = cgetstr(lc->lc_cap, cap, &res)) {
case -1:
if (res)
free(res);
return (def);
case -2:
syslog(LOG_ERR, "%s: getting capability %s: %m",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
default:
if (status >= 0)
break;
syslog(LOG_ERR, "%s: unexpected error with capability %s",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
}
if (isinfinite(res))
return (RLIM_INFINITY);
errno = 0;
q = 0;
sres = res;
while (*res) {
r = strtoq(res, &ep, 0);
if (!ep || ep == res ||
((r == QUAD_MIN || r == QUAD_MAX) && errno == ERANGE)) {
invalid:
syslog(LOG_ERR, "%s:%s=%s: invalid time",
lc->lc_class, cap, sres);
errno = ERANGE;
free(sres);
return (e);
}
switch (*ep++) {
case '\0':
--ep;
break;
case 's': case 'S':
break;
case 'm': case 'M':
r *= 60;
break;
case 'h': case 'H':
r *= 60 * 60;
break;
case 'd': case 'D':
r *= 60 * 60 * 24;
break;
case 'w': case 'W':
r *= 60 * 60 * 24 * 7;
break;
case 'y': case 'Y': /* Pretty absurd */
r *= 60 * 60 * 24 * 365;
break;
default:
goto invalid;
}
res = ep;
q += r;
}
free(sres);
return (q);
}
quad_t
login_getcapnum(login_cap_t *lc, const char *cap, quad_t def, quad_t e)
{
char *ep;
char *res = NULL;
int status;
quad_t q;
_DIAGASSERT(cap != NULL);
errno = 0;
if (!lc || !lc->lc_cap)
return (def);
switch (status = cgetstr(lc->lc_cap, cap, &res)) {
case -1:
if (res)
free(res);
return (def);
case -2:
syslog(LOG_ERR, "%s: getting capability %s: %m",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
default:
if (status >= 0)
break;
syslog(LOG_ERR, "%s: unexpected error with capability %s",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
}
if (isinfinite(res))
return (RLIM_INFINITY);
errno = 0;
q = strtoq(res, &ep, 0);
if (!ep || ep == res || ep[0] ||
((q == QUAD_MIN || q == QUAD_MAX) && errno == ERANGE)) {
syslog(LOG_ERR, "%s:%s=%s: invalid number",
lc->lc_class, cap, res);
errno = ERANGE;
free(res);
return (e);
}
free(res);
return (q);
}
quad_t
login_getcapsize(login_cap_t *lc, const char *cap, quad_t def, quad_t e)
{
char *ep;
char *res = NULL;
int status;
quad_t q;
_DIAGASSERT(cap != NULL);
errno = 0;
if (!lc || !lc->lc_cap)
return (def);
switch (status = cgetstr(lc->lc_cap, cap, &res)) {
case -1:
if (res)
free(res);
return (def);
case -2:
syslog(LOG_ERR, "%s: getting capability %s: %m",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
default:
if (status >= 0)
break;
syslog(LOG_ERR, "%s: unexpected error with capability %s",
lc->lc_class, cap);
errno = ERANGE;
if (res)
free(res);
return (e);
}
errno = 0;
q = strtolimit(res, &ep, 0);
if (!ep || ep == res || (ep[0] && ep[1]) ||
((q == QUAD_MIN || q == QUAD_MAX) && errno == ERANGE)) {
syslog(LOG_ERR, "%s:%s=%s: invalid size",
lc->lc_class, cap, res);
errno = ERANGE;
free(res);
return (e);
}
free(res);
return (q);
}
int
login_getcapbool(login_cap_t *lc, const char *cap, u_int def)
{
_DIAGASSERT(cap != NULL);
if (!lc || !lc->lc_cap)
return (def);
return (cgetcap(lc->lc_cap, cap, ':') != NULL);
}
void
login_close(login_cap_t *lc)
{
if (lc) {
if (lc->lc_class)
free(lc->lc_class);
if (lc->lc_cap)
free(lc->lc_cap);
if (lc->lc_style)
free(lc->lc_style);
free(lc);
}
}
#define R_CTIME 1
#define R_CSIZE 2
#define R_CNUMB 3
static struct {
int what;
int type;
const char *name;
} r_list[] = {
{ RLIMIT_CPU, R_CTIME, "cputime", },
{ RLIMIT_FSIZE, R_CSIZE, "filesize", },
{ RLIMIT_DATA, R_CSIZE, "datasize", },
{ RLIMIT_STACK, R_CSIZE, "stacksize", },
{ RLIMIT_RSS, R_CSIZE, "memoryuse", },
{ RLIMIT_MEMLOCK, R_CSIZE, "memorylocked", },
{ RLIMIT_NPROC, R_CNUMB, "maxproc", },
{ RLIMIT_NOFILE, R_CNUMB, "openfiles", },
{ RLIMIT_CORE, R_CSIZE, "coredumpsize", },
{ RLIMIT_SBSIZE, R_CSIZE, "sbsize", },
{ -1, 0, 0 }
};
static int
gsetrl(login_cap_t *lc, int what, const char *name, int type)
{
struct rlimit rl;
struct rlimit r;
char name_cur[32];
char name_max[32];
_DIAGASSERT(name != NULL);
(void)snprintf(name_cur, sizeof(name_cur), "%s-cur", name);
(void)snprintf(name_max, sizeof(name_max), "%s-max", name);
if (getrlimit(what, &r)) {
syslog(LOG_ERR, "getting resource limit: %m");
return (-1);
}
#define RCUR r.rlim_cur
#define RMAX r.rlim_max
switch (type) {
case R_CTIME:
RCUR = login_getcaptime(lc, name, RCUR, RCUR);
RMAX = login_getcaptime(lc, name, RMAX, RMAX);
rl.rlim_cur = login_getcaptime(lc, name_cur, RCUR, RCUR);
rl.rlim_max = login_getcaptime(lc, name_max, RMAX, RMAX);
break;
case R_CSIZE:
RCUR = login_getcapsize(lc, name, RCUR, RCUR);
RMAX = login_getcapsize(lc, name, RMAX, RMAX);
rl.rlim_cur = login_getcapsize(lc, name_cur, RCUR, RCUR);
rl.rlim_max = login_getcapsize(lc, name_max, RMAX, RMAX);
break;
case R_CNUMB:
RCUR = login_getcapnum(lc, name, RCUR, RCUR);
RMAX = login_getcapnum(lc, name, RMAX, RMAX);
rl.rlim_cur = login_getcapnum(lc, name_cur, RCUR, RCUR);
rl.rlim_max = login_getcapnum(lc, name_max, RMAX, RMAX);
break;
default:
syslog(LOG_ERR, "%s: invalid type %d setting resource limit %s",
lc->lc_class, type, name);
return (-1);
}
if (setrlimit(what, &rl)) {
syslog(LOG_ERR, "%s: setting resource limit %s: %m",
lc->lc_class, name);
return (-1);
}
#undef RCUR
#undef RMAX
return (0);
}
static int
/*ARGSUSED*/
envset(void *envp __unused, const char *name, const char *value, int overwrite)
{
return setenv(name, value, overwrite);
}
int
setuserenv(login_cap_t *lc, envfunc_t senv, void *envp)
{
const char *stop = ", \t";
size_t i, count;
char *ptr;
char **res;
char *str = login_getcapstr(lc, "setenv", NULL, NULL);
if (str == NULL || *str == '\0')
return 0;
/*
* count the sub-strings, this may over-count since we don't
* account for escaped delimiters.
*/
for (i = 1, ptr = str; *ptr; i++) {
ptr += strcspn(ptr, stop);
if (*ptr)
ptr++;
}
/* allocate ptr array and string */
count = i;
res = malloc(count * sizeof(char *) + strlen(str) + 1);
if (!res)
return -1;
ptr = (char *)(void *)&res[count];
(void)strcpy(ptr, str);
/* split string */
for (i = 0; (res[i] = stresep(&ptr, stop, '\\')) != NULL; )
if (*res[i])
i++;
count = i;
for (i = 0; i < count; i++) {
if ((ptr = strchr(res[i], '=')) != NULL)
*ptr++ = '\0';
else
ptr = NULL;
(void)(*senv)(envp, res[i], ptr ? ptr : "", 1);
}
free(res);
return 0;
}
int
setclasscontext(const char *class, u_int flags)
{
int ret;
login_cap_t *lc;
flags &= LOGIN_SETRESOURCES | LOGIN_SETPRIORITY | LOGIN_SETUMASK |
LOGIN_SETPATH;
lc = login_getclass(class);
ret = lc ? setusercontext(lc, NULL, 0, flags) : -1;
login_close(lc);
return (ret);
}
int
setusercontext(login_cap_t *lc, struct passwd *pwd, uid_t uid, u_int flags)
{
char per_user_tmp[MAXPATHLEN + 1];
const char *component_name;
login_cap_t *flc;
quad_t p;
int i;
ssize_t len;
flc = NULL;
if (!lc)
flc = lc = login_getclass(pwd ? pwd->pw_class : NULL);
/*
* Without the pwd entry being passed we cannot set either
* the group or the login. We could complain about it.
*/
if (pwd == NULL)
flags &= ~(LOGIN_SETGROUP|LOGIN_SETLOGIN);
#ifdef LOGIN_OSETGROUP
if (pwd == NULL)
flags &= ~LOGIN_OSETGROUP;
if (flags & LOGIN_OSETGROUP)
flags = (flags & ~LOGIN_OSETGROUP) | LOGIN_SETGROUP;
#endif
if (flags & LOGIN_SETRESOURCES)
for (i = 0; r_list[i].name; ++i)
(void)gsetrl(lc, r_list[i].what, r_list[i].name,
r_list[i].type);
if (flags & LOGIN_SETPRIORITY) {
p = login_getcapnum(lc, "priority", (quad_t)0, (quad_t)0);
if (setpriority(PRIO_PROCESS, 0, (int)p) == -1)
syslog(LOG_ERR, "%s: setpriority: %m", lc->lc_class);
}
if (flags & LOGIN_SETUMASK) {
p = login_getcapnum(lc, "umask", (quad_t) LOGIN_DEFUMASK,
(quad_t)LOGIN_DEFUMASK);
umask((mode_t)p);
}
if (flags & LOGIN_SETGID) {
if (setgid(pwd->pw_gid) == -1) {
syslog(LOG_ERR, "setgid(%d): %m", pwd->pw_gid);
login_close(flc);
return (-1);
}
}
if (flags & LOGIN_SETGROUPS) {
if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) {
syslog(LOG_ERR, "initgroups(%s,%d): %m",
pwd->pw_name, pwd->pw_gid);
login_close(flc);
return (-1);
}
}
/* Create per-user temporary directories if needed. */
if ((len = readlink("/tmp", per_user_tmp,
sizeof(per_user_tmp) - 6)) != -1) {
static const char atuid[] = "/@ruid";
char *lp;
/* readlink does not nul-terminate the string */
per_user_tmp[len] = '\0';
/* Check if it's magic symlink. */
lp = strstr(per_user_tmp, atuid);
if (lp != NULL && *(lp + (sizeof(atuid) - 1)) == '\0') {
lp++;
if (snprintf(lp, 11, "/%u", pwd->pw_uid) > 10) {
syslog(LOG_ERR, "real temporary path too long");
login_close(flc);
return (-1);
}
if (mkdir(per_user_tmp, S_IRWXU) != -1) {
if (chown(per_user_tmp, pwd->pw_uid,
pwd->pw_gid)) {
component_name = "chown";
goto out;
}
/*
* Must set sticky bit for tmp directory, some
* programs rely on this.
*/
if(chmod(per_user_tmp, S_IRWXU | S_ISVTX)) {
component_name = "chmod";
goto out;
}
} else {
if (errno != EEXIST) {
component_name = "mkdir";
goto out;
} else {
/*
* We must ensure that we own the
* directory and that is has the correct
* permissions, otherwise a DOS attack
* is possible.
*/
struct stat sb;
if (stat(per_user_tmp, &sb) == -1) {
component_name = "stat";
goto out;
}
if (sb.st_uid != pwd->pw_uid) {
if (chown(per_user_tmp,
pwd->pw_uid, pwd->pw_gid)) {
component_name = "chown";
goto out;
}
}
if (sb.st_mode != (S_IRWXU | S_ISVTX)) {
if (chmod(per_user_tmp,
S_IRWXU | S_ISVTX)) {
component_name = "chmod";
goto out;
}
}
}
}
}
}
errno = 0;
if (flags & LOGIN_SETLOGIN)
if (setlogin(pwd->pw_name) == -1) {
syslog(LOG_ERR, "setlogin(%s) failure: %m",
pwd->pw_name);
login_close(flc);
return (-1);
}
if (flags & LOGIN_SETUSER)
if (setuid(uid) == -1) {
syslog(LOG_ERR, "setuid(%d): %m", uid);
login_close(flc);
return (-1);
}
if (flags & LOGIN_SETENV)
setuserenv(lc, envset, NULL);
if (flags & LOGIN_SETPATH)
setuserpath(lc, pwd ? pwd->pw_dir : "", envset, NULL);
login_close(flc);
return (0);
out:
if (component_name != NULL) {
syslog(LOG_ERR, "%s %s: %m", component_name, per_user_tmp);
login_close(flc);
return (-1);
} else {
syslog(LOG_ERR, "%s: %m", per_user_tmp);
login_close(flc);
return (-1);
}
}
void
setuserpath(login_cap_t *lc, const char *home, envfunc_t senv, void *envp)
{
size_t hlen, plen;
int cnt = 0;
char *path;
const char *cpath;
char *p, *q;
_DIAGASSERT(home != NULL);
hlen = strlen(home);
p = path = login_getcapstr(lc, "path", NULL, NULL);
if (p) {
while (*p)
if (*p++ == '~')
++cnt;
plen = (p - path) + cnt * (hlen + 1) + 1;
p = path;
q = path = malloc(plen);
if (q) {
while (*p) {
p += strspn(p, " \t");
if (*p == '\0')
break;
plen = strcspn(p, " \t");
if (hlen == 0 && *p == '~') {
p += plen;
continue;
}
if (q != path)
*q++ = ':';
if (*p == '~') {
strcpy(q, home);
q += hlen;
++p;
--plen;
}
memcpy(q, p, plen);
p += plen;
q += plen;
}
*q = '\0';
cpath = path;
} else
cpath = _PATH_DEFPATH;
} else
cpath = _PATH_DEFPATH;
if ((*senv)(envp, "PATH", cpath, 1))
warn("could not set PATH");
}
/*
* Convert an expression of the following forms
* 1) A number.
* 2) A number followed by a b (mult by 512).
* 3) A number followed by a k (mult by 1024).
* 5) A number followed by a m (mult by 1024 * 1024).
* 6) A number followed by a g (mult by 1024 * 1024 * 1024).
* 7) A number followed by a t (mult by 1024 * 1024 * 1024 * 1024).
* 8) Two or more numbers (with/without k,b,m,g, or t).
* separated by x (also * for backwards compatibility), specifying
* the product of the indicated values.
*/
static u_quad_t
strtosize(const char *str, char **endptr, int radix)
{
u_quad_t num, num2;
char *expr, *expr2;
_DIAGASSERT(str != NULL);
/* endptr may be NULL */
errno = 0;
num = strtouq(str, &expr, radix);
if (errno || expr == str) {
if (endptr)
*endptr = expr;
return (num);
}
switch(*expr) {
case 'b': case 'B':
num = multiply(num, (u_quad_t)512);
++expr;
break;
case 'k': case 'K':
num = multiply(num, (u_quad_t)1024);
++expr;
break;
case 'm': case 'M':
num = multiply(num, (u_quad_t)1024 * 1024);
++expr;
break;
case 'g': case 'G':
num = multiply(num, (u_quad_t)1024 * 1024 * 1024);
++expr;
break;
case 't': case 'T':
num = multiply(num, (u_quad_t)1024 * 1024);
num = multiply(num, (u_quad_t)1024 * 1024);
++expr;
break;
}
if (errno)
goto erange;
switch(*expr) {
case '*': /* Backward compatible. */
case 'x':
num2 = strtosize(expr+1, &expr2, radix);
if (errno) {
expr = expr2;
goto erange;
}
if (expr2 == expr + 1) {
if (endptr)
*endptr = expr;
return (num);
}
expr = expr2;
num = multiply(num, num2);
if (errno)
goto erange;
break;
}
if (endptr)
*endptr = expr;
return (num);
erange:
if (endptr)
*endptr = expr;
errno = ERANGE;
return (UQUAD_MAX);
}
static u_quad_t
strtolimit(const char *str, char **endptr, int radix)
{
_DIAGASSERT(str != NULL);
/* endptr may be NULL */
if (isinfinite(str)) {
if (endptr)
*endptr = (char *)__UNCONST(str) + strlen(str);
return ((u_quad_t)RLIM_INFINITY);
}
return (strtosize(str, endptr, radix));
}
static int
isinfinite(const char *s)
{
static const char *infs[] = {
"infinity",
"inf",
"unlimited",
"unlimit",
NULL
};
const char **i;
_DIAGASSERT(s != NULL);
for (i = infs; *i; i++) {
if (!strcasecmp(s, *i))
return 1;
}
return 0;
}
static u_quad_t
multiply(u_quad_t n1, u_quad_t n2)
{
static int bpw = 0;
u_quad_t m;
u_quad_t r;
int b1, b2;
/*
* Get rid of the simple cases
*/
if (n1 == 0 || n2 == 0)
return (0);
if (n1 == 1)
return (n2);
if (n2 == 1)
return (n1);
/*
* sizeof() returns number of bytes needed for storage.
* This may be different from the actual number of useful bits.
*/
if (!bpw) {
bpw = sizeof(u_quad_t) * 8;
while (((u_quad_t)1 << (bpw-1)) == 0)
--bpw;
}
/*
* First check the magnitude of each number. If the sum of the
* magnatude is way to high, reject the number. (If this test
* is not done then the first multiply below may overflow.)
*/
for (b1 = bpw; (((u_quad_t)1 << (b1-1)) & n1) == 0; --b1)
;
for (b2 = bpw; (((u_quad_t)1 << (b2-1)) & n2) == 0; --b2)
;
if (b1 + b2 - 2 > bpw) {
errno = ERANGE;
return (UQUAD_MAX);
}
/*
* Decompose the multiplication to be:
* h1 = n1 & ~1
* h2 = n2 & ~1
* l1 = n1 & 1
* l2 = n2 & 1
* (h1 + l1) * (h2 + l2)
* (h1 * h2) + (h1 * l2) + (l1 * h2) + (l1 * l2)
*
* Since h1 && h2 do not have the low bit set, we can then say:
*
* (h1>>1 * h2>>1 * 4) + ...
*
* So if (h1>>1 * h2>>1) > (1<<(bpw - 2)) then the result will
* overflow.
*
* Finally, if MAX - ((h1 * l2) + (l1 * h2) + (l1 * l2)) < (h1*h2)
* then adding in residual amout will cause an overflow.
*/
m = (n1 >> 1) * (n2 >> 1);
if (m >= ((u_quad_t)1 << (bpw-2))) {
errno = ERANGE;
return (UQUAD_MAX);
}
m *= 4;
r = (n1 & n2 & 1)
+ (n2 & 1) * (n1 & ~(u_quad_t)1)
+ (n1 & 1) * (n2 & ~(u_quad_t)1);
if ((u_quad_t)(m + r) < m) {
errno = ERANGE;
return (UQUAD_MAX);
}
m += r;
return (m);
}
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