linux-kernel - [PATCH] random: fix add_hwgenerator

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Date:   Mon,  4 Apr 2022 18:04:42 +0300
From:   Jan Varho <jan.varho@...il.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "Theodore Ts'o" <tytso@....edu>
Cc:     linux-kernel@...r.kernel.org, Jan Varho <jan.varho@...il.com>
Subject: [PATCH] random: fix add_hwgenerator_randomness entropy accounting

add_hwgenerator_randomness tries to only use the required amound of input
for fast init, but credits all the entropy if even a byte was left over.

Fix by not crediting entropy if any input was consumed for fast init.

Signed-off-by: Jan Varho <jan.varho@...il.com>
---
 drivers/char/random.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1d8242969751..fb20178f1044 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1141,12 +1141,10 @@ void add_hwgenerator_randomness(const void *buffer, size_t count,
 				size_t entropy)
 {
 	if (unlikely(crng_init == 0 && entropy < POOL_MIN_BITS)) {
-		size_t ret = crng_pre_init_inject(buffer, count, true);
-		mix_pool_bytes(buffer, ret);
-		count -= ret;
-		buffer += ret;
-		if (!count || crng_init == 0)
+		if (crng_pre_init_inject(buffer, count, true) > 0) {
+			mix_pool_bytes(buffer, count);
 			return;
+		}
 	}
 
 	/*
-- 
2.25.1