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authorJason A. Donenfeld <Jason@zx2c4.com>2021-12-30 00:10:06 +0300
committerJason A. Donenfeld <Jason@zx2c4.com>2022-01-07 02:25:25 +0300
commit57826feeedb63b091f807ba8325d736775d39afd (patch)
tree8993c8b28288d04fdffde437c854b34338facb3f /drivers/char
parent73c7733f122e8d0107f88655a12011f68f69e74b (diff)
downloadlinux-57826feeedb63b091f807ba8325d736775d39afd.tar.xz
random: mix bootloader randomness into pool
If we're trusting bootloader randomness, crng_fast_load() is called by add_hwgenerator_randomness(), which sets us to crng_init==1. However, usually it is only called once for an initial 64-byte push, so bootloader entropy will not mix any bytes into the input pool. So it's conceivable that crng_init==1 when crng_initialize_primary() is called later, but then the input pool is empty. When that happens, the crng state key will be overwritten with extracted output from the empty input pool. That's bad. In contrast, if we're not trusting bootloader randomness, we call crng_slow_load() *and* we call mix_pool_bytes(), so that later crng_initialize_primary() isn't drawing on nothing. In order to prevent crng_initialize_primary() from extracting an empty pool, have the trusted bootloader case mirror that of the untrusted bootloader case, mixing the input into the pool. [linux@dominikbrodowski.net: rewrite commit message] Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'drivers/char')
-rw-r--r--drivers/char/random.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 21166188b7e1..9d4e1907e4b1 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2298,6 +2298,7 @@ void add_hwgenerator_randomness(const char *buffer, size_t count,
if (unlikely(crng_init == 0)) {
size_t ret = crng_fast_load(buffer, count);
+ mix_pool_bytes(poolp, buffer, ret);
count -= ret;
buffer += ret;
if (!count || crng_init == 0)