From 09ff7417a6aa7d59d43f2d5bcc39ee42ba01013f Mon Sep 17 00:00:00 2001
From: Nicolai Stange <nstange@suse.de>
Date: Tue, 30 Nov 2021 11:00:27 +0100
Subject: [PATCH 3/3] crypto: jitter - quit sample collection loop upon RCT
 failure
References: jsc#SLE-21132,bsc#1191259
Patch-mainline: v5.17-rc1
Git-commit: 710ce4b88f9a93a6b2c2267e8f27ba65af3cb6ac

The jitterentropy collection loop in jent_gen_entropy() can in principle
run indefinitely without making any progress if it only receives stuck
measurements as determined by jent_stuck(). After 31 consecutive stuck
samples, the Repetition Count Test (RCT) would fail anyway and the
jitterentropy RNG instances moved into ->health_failure == 1 state.
jent_gen_entropy()'s caller, jent_read_entropy() would then check for
this ->health_failure condition and return an error if found set. It
follows that there's absolutely no point in continuing the collection loop
in jent_gen_entropy() once the RCT has failed.

Make the jitterentropy collection loop more robust by terminating it upon
jent_health_failure() so that it won't continue to run indefinitely without
making any progress.

Signed-off-by: Nicolai Stange <nstange@suse.de>
---
 crypto/jitterentropy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -547,7 +547,7 @@ static void jent_gen_entropy(struct rand
 	/* priming of the ->prev_time value */
 	jent_measure_jitter(ec);
 
-	while (1) {
+	while (!jent_health_failure(ec)) {
 		/* If a stuck measurement is received, repeat measurement */
 		if (jent_measure_jitter(ec))
 			continue;