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Rely on /dev/urandom

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This removes quite a bit of code. All reasonable systems have /dev/urandom
these days. Linux, Solaris and the BSDs do.  In case we find a system
without /dev/urandom, we will have to go hunting in other libraries.

The main reason for this is speed: On Ubuntu 14.04 doing direct reads from
/dev/urandom is 2-3 times faster than our md4 based code. On virtualized
FreeBSD 10 the difference is even larger.

My first approach was to use fopen/fread. It was even faster, but less
than twice as fast. So I thought we could save the additional complexity
when having to deal with throwing away buffers when forking and the
additional memory footprint per process.

With this simple generate_random_buffer it will be easier to adapt new
syscalls to get randomness.

Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Tue Oct 13 04:25:39 CEST 2015 on sn-devel-104
This commit is contained in:
Volker Lendecke 2015-10-02 00:27:22 +02:00 committed by Jeremy Allison
parent 5380f7b636
commit e73ccc06ef
10 changed files with 18 additions and 376 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

261
lib/util/genrand.c
View File

@ -21,268 +21,41 @@
#include "replace.h"
#include "system/filesys.h"
#include "../lib/crypto/crypto.h"
#include "lib/util/genrand.h"
#include "sys_rw_data.h"
#include "lib/util/blocking.h"
#include "lib/util/time_basic.h"
#include "lib/util/byteorder.h"
/**
* @file
* @brief Random number generation
*/
static unsigned char hash[258];
static uint32_t counter;
static bool done_reseed = false;
static unsigned int bytes_since_reseed = 0;
static int urand_fd = -1;
static void (*reseed_callback)(void *userdata, int *newseed);
static void *reseed_callback_userdata = NULL;
/**
Copy any user given reseed data.
**/
_PUBLIC_ void set_rand_reseed_callback(void (*fn)(void *, int *), void *userdata)
static void open_urandom(void)
{
reseed_callback = fn;
reseed_callback_userdata = userdata;
set_need_random_reseed();
}
/**
* Tell the random number generator it needs to reseed.
*/
_PUBLIC_ void set_need_random_reseed(void)
{
done_reseed = false;
bytes_since_reseed = 0;
}
static void get_rand_reseed_data(int *reseed_data)
{
if (reseed_callback) {
reseed_callback(reseed_callback_userdata, reseed_data);
} else {
*reseed_data = 0;
}
}
/****************************************************************
Setup the seed.
*****************************************************************/
static void seed_random_stream(unsigned char *seedval, size_t seedlen)
{
unsigned char j = 0;
size_t ind;
for (ind = 0; ind < 256; ind++)
hash[ind] = (unsigned char)ind;
for( ind = 0; ind < 256; ind++) {
unsigned char tc;
j += (hash[ind] + seedval[ind%seedlen]);
tc = hash[ind];
hash[ind] = hash[j];
hash[j] = tc;
}
hash[256] = 0;
hash[257] = 0;
}
/****************************************************************
Get datasize bytes worth of random data.
*****************************************************************/
static void get_random_stream(unsigned char *data, size_t datasize)
{
unsigned char index_i = hash[256];
unsigned char index_j = hash[257];
size_t ind;
for( ind = 0; ind < datasize; ind++) {
unsigned char tc;
unsigned char t;
index_i++;
index_j += hash[index_i];
tc = hash[index_i];
hash[index_i] = hash[index_j];
hash[index_j] = tc;
t = hash[index_i] + hash[index_j];
data[ind] = hash[t];
}
hash[256] = index_i;
hash[257] = index_j;
}
/****************************************************************
Get a 16 byte hash from the contents of a file.
Note that the hash is initialised, because the extra entropy is not
worth the valgrind pain.
*****************************************************************/
static void do_filehash(const char *fname, unsigned char *the_hash)
{
unsigned char buf[1011]; /* deliberate weird size */
unsigned char tmp_md4[16];
int fd, n;
ZERO_STRUCT(tmp_md4);
fd = open(fname,O_RDONLY,0);
if (fd == -1)
if (urand_fd != -1) {
return;
while ((n = read(fd, (char *)buf, sizeof(buf))) > 0) {
mdfour(tmp_md4, buf, n);
for (n=0;n<16;n++)
the_hash[n] ^= tmp_md4[n];
}
close(fd);
urand_fd = open( "/dev/urandom", O_RDONLY,0);
if (urand_fd == -1) {
abort();
}
smb_set_close_on_exec(urand_fd);
}
/**************************************************************
Try and get a good random number seed. Try a number of
different factors. Firstly, try /dev/urandom - use if exists.
We use /dev/urandom as a read of /dev/random can block if
the entropy pool dries up. This leads clients to timeout
or be very slow on connect.
If we can't use /dev/urandom then seed the stream random generator
above...
**************************************************************/
static int do_reseed(int fd)
{
unsigned char seed_inbuf[40];
uint32_t v1, v2; struct timeval tval; pid_t mypid;
int reseed_data = 0;
if (fd == -1) {
fd = open( "/dev/urandom", O_RDONLY,0);
if (fd != -1) {
smb_set_close_on_exec(fd);
}
}
if (fd != -1
&& (read(fd, seed_inbuf, sizeof(seed_inbuf)) == sizeof(seed_inbuf))) {
seed_random_stream(seed_inbuf, sizeof(seed_inbuf));
return fd;
}
/* Add in some secret file contents */
do_filehash("/etc/shadow", &seed_inbuf[0]);
/*
* Add the counter, time of day, and pid.
*/
GetTimeOfDay(&tval);
mypid = getpid();
v1 = (counter++) + mypid + tval.tv_sec;
v2 = (counter++) * mypid + tval.tv_usec;
SIVAL(seed_inbuf, 32, v1 ^ IVAL(seed_inbuf, 32));
SIVAL(seed_inbuf, 36, v2 ^ IVAL(seed_inbuf, 36));
/*
* Add any user-given reseed data.
*/
get_rand_reseed_data(&reseed_data);
if (reseed_data) {
size_t i;
for (i = 0; i < sizeof(seed_inbuf); i++)
seed_inbuf[i] ^= ((char *)(&reseed_data))[i % sizeof(reseed_data)];
}
seed_random_stream(seed_inbuf, sizeof(seed_inbuf));
return -1;
}
/**
Interface to the (hopefully) good crypto random number generator.
Will use our internal PRNG if more than 40 bytes of random generation
has been requested, otherwise tries to read from /dev/random
**/
_PUBLIC_ void generate_random_buffer(uint8_t *out, int len)
{
unsigned char md4_buf[64];
unsigned char tmp_buf[16];
unsigned char *p;
ssize_t rw_ret;
if(!done_reseed) {
bytes_since_reseed += len;
open_urandom();
/* Magic constant to try and avoid reading 40 bytes
* and setting up the PRNG if the app only ever wants
* a few bytes */
if (bytes_since_reseed < 40) {
if (urand_fd == -1) {
urand_fd = open( "/dev/urandom", O_RDONLY,0);
if (urand_fd != -1) {
smb_set_close_on_exec(urand_fd);
}
}
if(urand_fd != -1 && (read(urand_fd, out, len) == len)) {
return;
}
}
urand_fd = do_reseed(urand_fd);
done_reseed = true;
}
/*
* Generate random numbers in chunks of 64 bytes,
* then md4 them & copy to the output buffer.
* This way the raw state of the stream is never externally
* seen.
*/
p = out;
while(len > 0) {
int copy_len = len > 16 ? 16 : len;
get_random_stream(md4_buf, sizeof(md4_buf));
mdfour(tmp_buf, md4_buf, sizeof(md4_buf));
memcpy(p, tmp_buf, copy_len);
p += copy_len;
len -= copy_len;
rw_ret = read_data(urand_fd, out, len);
if (rw_ret != len) {
abort();
}
}
/**
Interface to the (hopefully) good crypto random number generator.
Will always use /dev/urandom if available.
**/
/*
* Keep generate_secret_buffer in case we ever want to do something
* different
*/
_PUBLIC_ void generate_secret_buffer(uint8_t *out, int len)
{
if (urand_fd == -1) {
urand_fd = open( "/dev/urandom", O_RDONLY,0);
if (urand_fd != -1) {
smb_set_close_on_exec(urand_fd);
}
}
if(urand_fd != -1 && (read(urand_fd, out, len) == len)) {
return;
}
generate_random_buffer(out, len);
}

11
lib/util/genrand.h
View File

@ -19,17 +19,6 @@
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
Copy any user given reseed data.
**/
void set_rand_reseed_callback(void (*fn)(void *, int *), void *userdata);
/**
* Tell the random number generator it needs to reseed.
*/
void set_need_random_reseed(void);
/**
Interface to the (hopefully) good crypto random number generator.
Will use our internal PRNG if more than 40 bytes of random generation

12
lib/util/tests/genrand.c
View File

@ -23,17 +23,6 @@
#include "torture/torture.h"
#include "torture/local/proto.h"
static void dummy_reseed(void *userdata, int *d)
{
*d = 42;
}
static bool test_reseed_callback(struct torture_context *tctx)
{
set_rand_reseed_callback(dummy_reseed, NULL);
return true;
}
static bool test_check_password_quality(struct torture_context *tctx)
{
torture_assert(tctx, !check_password_quality(""), "empty password");
@ -64,7 +53,6 @@ static bool test_generate_random_str(struct torture_context *tctx)
struct torture_suite *torture_local_genrand(TALLOC_CTX *mem_ctx)
{
struct torture_suite *suite = torture_suite_create(mem_ctx, "genrand");
torture_suite_add_simple_test(suite, "reseed_callback", test_reseed_callback);
torture_suite_add_simple_test(suite, "check_password_quality", test_check_password_quality);
torture_suite_add_simple_test(suite, "generate_random_str", test_generate_random_str);
return suite;

2
lib/util/wscript_build
View File

@ -84,7 +84,7 @@ if not bld.env.SAMBA_UTIL_CORE_ONLY:
bld.SAMBA_LIBRARY('genrand',
source='genrand.c',
deps='time-basic socket-blocking LIBCRYPTO',
deps='replace socket-blocking sys_rw',
local_include=False,
private_library=True)

6
source3/lib/util.c
View File

@ -441,12 +441,6 @@ NTSTATUS reinit_after_fork(struct messaging_context *msg_ctx,
reinit_after_fork_pipe[1] = -1;
}
/* Reset the state of the random
* number generation system, so
* children do not get the same random
* numbers as each other */
set_need_random_reseed();
/* tdb needs special fork handling */
if (tdb_reopen_all(parent_longlived ? 1 : 0) != 0) {
DEBUG(0,("tdb_reopen_all failed.\n"));

29
source3/passdb/secrets.c
View File

@ -37,28 +37,10 @@
static struct db_context *db_ctx;
/**
* Use a TDB to store an incrementing random seed.
*
* Initialised to the current pid, the very first time Samba starts,
* and incremented by one each time it is needed.
*
* @note Not called by systems with a working /dev/urandom.
*/
static void get_rand_seed(void *userdata, int *new_seed)
{
*new_seed = getpid();
if (db_ctx) {
dbwrap_trans_change_int32_atomic_bystring(
db_ctx, "INFO/random_seed", new_seed, 1);
}
}
/* open up the secrets database with specified private_dir path */
bool secrets_init_path(const char *private_dir)
{
char *fname = NULL;
unsigned char dummy;
TALLOC_CTX *frame;
if (db_ctx != NULL) {
@ -86,17 +68,6 @@ bool secrets_init_path(const char *private_dir)
return False;
}
/**
* Set a reseed function for the crypto random generator
*
* This avoids a problem where systems without /dev/urandom
* could send the same challenge to multiple clients
*/
set_rand_reseed_callback(get_rand_seed, NULL);
/* Ensure that the reseed is done now, while we are root, etc */
generate_random_buffer(&dummy, sizeof(dummy));
TALLOC_FREE(frame);
return True;
}

53
source4/param/secrets.c
View File

@ -32,59 +32,6 @@
#include "librpc/gen_ndr/ndr_security.h"
#include "dsdb/samdb/samdb.h"
/**
* Use a TDB to store an incrementing random seed.
*
* Initialised to the current pid, the very first time Samba starts,
* and incremented by one each time it is needed.
*
* @note Not called by systems with a working /dev/urandom.
*/
static void get_rand_seed(struct tdb_wrap *secretsdb, int *new_seed)
{
*new_seed = getpid();
if (secretsdb != NULL) {
tdb_change_int32_atomic(secretsdb->tdb, "INFO/random_seed", new_seed, 1);
}
}
/**
* open up the randseed database and set the random number generator callback
*/
bool randseed_init(TALLOC_CTX *mem_ctx, struct loadparm_context *lp_ctx)
{
char *fname;
uint8_t dummy;
struct tdb_wrap *tdb;
fname = lpcfg_private_path(mem_ctx, lp_ctx, "randseed.tdb");
tdb = tdb_wrap_open(mem_ctx, fname,
lpcfg_tdb_hash_size(lp_ctx, fname),
lpcfg_tdb_flags(lp_ctx, TDB_DEFAULT),
O_RDWR|O_CREAT, 0600);
if (!tdb) {
DEBUG(0,("Failed to open %s\n", fname));
talloc_free(fname);
return false;
}
talloc_free(fname);
/**
* Set a reseed function for the crypto random generator
*
* This avoids a problem where systems without /dev/urandom
* could send the same challenge to multiple clients
*/
set_rand_reseed_callback((void (*) (void *, int *))get_rand_seed, tdb);
/* Ensure that the reseed is done now, while we are root, etc */
generate_random_buffer(&dummy, sizeof(dummy));
return true;
}
/**
connect to the secrets ldb
*/

8
source4/param/secrets.h
View File

@ -28,14 +28,6 @@
#define SECRETS_PRINCIPAL_SEARCH "(&(|(realm=%s)(flatname=%s))(servicePrincipalName=%s))"
#define SECRETS_LDAP_FILTER "(&(objectclass=ldapSecret)(cn=SAMDB Credentials))"
/**
* Use a TDB to store an incrementing random seed.
*
* Initialised to the current pid, the very first time Samba starts,
* and incremented by one each time it is needed.
*
* @note Not called by systems with a working /dev/urandom.
*/
struct loadparm_context;
struct tevent_context;
struct ldb_message;

6
source4/smbd/process_standard.c
View File

@ -277,9 +277,6 @@ static void standard_accept_connection(struct tevent_context *ev,
child_pipe[1] = -1;
}
/* Ensure that the forked children do not expose identical random streams */
set_need_random_reseed();
/* setup the process title */
c = socket_get_peer_addr(sock2, ev);
s = socket_get_my_addr(sock2, ev);
@ -356,9 +353,6 @@ static void standard_new_task(struct tevent_context *ev,
child_pipe[1] = -1;
}
/* Ensure that the forked children do not expose identical random streams */
set_need_random_reseed();
setproctitle("task %s server_id[%d]", service_name, (int)pid);
/* setup this new task. Cluster ID is PID based for this process model */

6
source4/smbd/server.c
View File

@ -392,12 +392,6 @@ static int binary_smbd_main(const char *binary_name, int argc, const char *argv[
pidfile_create(lpcfg_pid_directory(cmdline_lp_ctx), binary_name);
/* Set up a database to hold a random seed, in case we don't
* have /dev/urandom */
if (!randseed_init(talloc_autofree_context(), cmdline_lp_ctx)) {
return 1;
}
if (lpcfg_server_role(cmdline_lp_ctx) == ROLE_ACTIVE_DIRECTORY_DC) {
if (!open_schannel_session_store(talloc_autofree_context(), cmdline_lp_ctx)) {
exit_daemon("Samba cannot open schannel store for secured NETLOGON operations.", EACCES);