Change in osmocom-bb[master]: Move from libc random() to osmo_get_rand_id

[Holger Freyther]

Holger Freyther has uploaded this change for review. ( https://gerrit.osmocom.org/9914


Change subject: Move from libc random() to osmo_get_rand_id
......................................................................

Move from libc random() to osmo_get_rand_id

When starting multiple mobile in the same second, the libc random number
generator will be seeded to exactly the same value.

The random bits inside the RACH request(s) will be exactly the same
across multiple mobile and when the channel fails they all pick the same
randomized back-off timing.

Use stronger random numbers and replace all calls to random(2) with
osmo_get_rand_id. Add a fallback to try random().

Change-Id: Ie0cc64663cd4b90c027b79545dc5d3ac9d87b9dd
---
M src/host/layer23/src/mobile/gsm322.c
M src/host/layer23/src/mobile/gsm48_mm.c
M src/host/layer23/src/mobile/gsm48_rr.c
M src/host/layer23/src/mobile/settings.c
4 files changed, 18 insertions(+), 5 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmocom-bb refs/changes/14/9914/1

diff --git a/src/host/layer23/src/mobile/gsm322.c b/src/host/layer23/src/mobile/gsm322.c
index c3485b6..fc90c07 100644
--- a/src/host/layer23/src/mobile/gsm322.c
+++ b/src/host/layer23/src/mobile/gsm322.c
@@ -959,7 +959,9 @@
 			entries++;
 	}
 	while(entries) {
-		move = random() % entries;
+		if (osmo_get_rand_id((uint8_t *) &move, sizeof(move)) != 0)
+			move = random() % entries;
+		move = move % entries;
 		i = 0;
 		llist_for_each_entry(temp, &temp_list, entry) {
 			if (rxlev2dbm(temp->rxlev) > -85) {
diff --git a/src/host/layer23/src/mobile/gsm48_mm.c b/src/host/layer23/src/mobile/gsm48_mm.c
index a7af1f5..a36e7e8 100644
--- a/src/host/layer23/src/mobile/gsm48_mm.c
+++ b/src/host/layer23/src/mobile/gsm48_mm.c
@@ -30,6 +30,7 @@
 #include <osmocom/core/utils.h>
 #include <osmocom/gsm/gsm48.h>
 #include <osmocom/core/talloc.h>
+#include <osmocom/gsm/gsm_utils.h>
 
 #include <osmocom/bb/common/logging.h>
 #include <osmocom/bb/common/osmocom_data.h>
@@ -2099,7 +2100,9 @@
 			mm->t3212.timeout.tv_sec = current_time.tv_sec
 				+ (t % s->t3212);
 		} else {
-			uint32_t rand = random();
+			uint32_t rand;
+			if (osmo_get_rand_id((uint8_t *) &rand, sizeof(rand)) != 0)
+				rand = random();
 
 			LOGP(DMM, LOGL_INFO, "New T3212 while timer is not "
 				"running (value %d)\n", s->t3212);
diff --git a/src/host/layer23/src/mobile/gsm48_rr.c b/src/host/layer23/src/mobile/gsm48_rr.c
index dd3fe93..db2cb5e 100644
--- a/src/host/layer23/src/mobile/gsm48_rr.c
+++ b/src/host/layer23/src/mobile/gsm48_rr.c
@@ -71,6 +71,7 @@
 #include <osmocom/gsm/rsl.h>
 #include <osmocom/gsm/gsm48.h>
 #include <osmocom/core/bitvec.h>
+#include <osmocom/gsm/gsm_utils.h>
 
 #include <osmocom/bb/common/osmocom_data.h>
 #include <osmocom/bb/common/l1l2_interface.h>
@@ -1628,7 +1629,8 @@
 		}
 	}
 
-	chan_req = random();
+	if (osmo_get_rand_id((uint8_t *) &chan_req, sizeof(chan_req)) != 0)
+		chan_req = random();
 	chan_req &= rr->chan_req_mask;
 	chan_req |= rr->chan_req_val;
 
diff --git a/src/host/layer23/src/mobile/settings.c b/src/host/layer23/src/mobile/settings.c
index 7370b0a..80b0b48 100644
--- a/src/host/layer23/src/mobile/settings.c
+++ b/src/host/layer23/src/mobile/settings.c
@@ -23,6 +23,7 @@
 #include <errno.h>
 #include <string.h>
 #include <osmocom/core/talloc.h>
+#include <osmocom/gsm/gsm_utils.h>
 
 #include <osmocom/bb/mobile/app_mobile.h>
 #include <osmocom/bb/common/logging.h>
@@ -178,14 +179,19 @@
 {
 	int digits = set->imei_random;
 	char rand[16];
+	long rand_num;
 
 	if (digits <= 0)
 		return 0;
 	if (digits > 15)
 		digits = 15;
 
-	sprintf(rand, "%08ld", random() % 100000000);
-	sprintf(rand + 8, "%07ld", random() % 10000000);
+	if (osmo_get_rand_id((uint8_t *) &rand_num, sizeof(rand_num)) != 0)
+		rand_num = random();
+	sprintf(rand, "%08ld", rand_num % 100000000);
+	if (osmo_get_rand_id((uint8_t *) &rand_num, sizeof(rand_num)) != 0)
+		rand_num = random();
+	sprintf(rand + 8, "%07ld", rand_num % 10000000);
 
 	strcpy(set->imei + 15 - digits, rand + 15 - digits);
 	strncpy(set->imeisv, set->imei, 15);

-- 
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Gerrit-Project: osmocom-bb
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: Ie0cc64663cd4b90c027b79545dc5d3ac9d87b9dd
Gerrit-Change-Number: 9914
Gerrit-PatchSet: 1
Gerrit-Owner: Holger Freyther <holger at freyther.de>
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