(4/7) trust_pct

PATCH New Oliver Xymoron 1 participant 1 message Aug 23, 2002

Subsystems (2)

Proc sysctl Random number driver

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Oliver Xymoron

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2002-08-23 18:27 UTC #0 lore raw

PATCH 1/1 (4/7) trust_pct

This allows adding a bit of entropy for a configurable percentage of untrusted timer samples, controlled by a new sysctl. This defaults to 0 for safety, but can be used on headless machines without a hardware RNG to continue to use /dev/random with some confidence.

RML's patch to turn on SA_SAMPLE_RANDOM for most NICs is safe after this patch.

drivers/char/random.c +16 -0

diff -ur a/drivers/char/random.c b/drivers/char/random.c
@@ -694,6 +694,7 @@
 static struct timer_rand_state extract_timer_state;
 static struct timer_rand_state *irq_timer_state[NR_IRQS];
 static struct timer_rand_state *blkdev_timer_state[MAX_BLKDEV];
+static int trust_break=50, trust_pct=0, trust_min=0, trust_max=100;
 
 /*
  * This function adds entropy to the entropy "pool" by using timing

@@ -761,6 +762,17 @@
 
 		entropy = int_log2_16bits(delta);
 	}
+	else if(trust_pct)
+	{
+		/* Count an untrusted bit as entropy trust_pct% of the time */
+		trust_break+=trust_pct;
+		if(trust_break >= 100)
+		{
+			entropy=1;
+			trust_break-=100;
+		}
+	}
+
 	batch_entropy_store(num^time, entropy);
 }

@@ -1849,6 +1861,10 @@
 	{RANDOM_UUID, "uuid",
 	 NULL, 16, 0444, NULL,
 	 &proc_do_uuid, &uuid_strategy},
+	{RANDOM_TRUST_PCT, "trust_pct",
+	 &trust_pct, sizeof(int), 0644, NULL,
+	 &proc_dointvec_minmax, &sysctl_intvec, 0,
+	 &trust_min, &trust_max},
 	{0}
 };

include/linux/sysctl.h +2 -1

diff -ur a/include/linux/sysctl.h b/include/linux/sysctl.h
@@ -182,7 +182,8 @@
 	RANDOM_READ_THRESH=3,
 	RANDOM_WRITE_THRESH=4,
 	RANDOM_BOOT_ID=5,
-	RANDOM_UUID=6
+	RANDOM_UUID=6,
+	RANDOM_TRUST_PCT=7
 };
 
 /* /proc/sys/bus/isa */

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