From: "Jason A. Donenfeld" Jason@zx2c4.com
stable inclusion from stable-v5.10.119 commit 655a69cb41e008943ea2f0990141863159126b82 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 66e4c2b9541503d721e936cc3898c9f25f4591ff upstream.
Since we have a hash function that's really fast, and the goal of crng_slow_load() is reportedly to "touch all of the crng's state", we can just hash the old state together with the new state and call it a day. This way we dont need to reason about another LFSR or worry about various attacks there. This code is only ever used at early boot and then never again.
Cc: Theodore Ts'o tytso@mit.edu Reviewed-by: Dominik Brodowski linux@dominikbrodowski.net Reviewed-by: Eric Biggers ebiggers@google.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Acked-by: Xie XiuQi xiexiuqi@huawei.com --- drivers/char/random.c | 42 +++++++++++++++--------------------------- 1 file changed, 15 insertions(+), 27 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c index 626c53c21b7e..866b855c1609 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -477,42 +477,30 @@ static size_t crng_fast_load(const u8 *cp, size_t len) * all), and (2) it doesn't have the performance constraints of * crng_fast_load(). * - * So we do something more comprehensive which is guaranteed to touch - * all of the primary_crng's state, and which uses a LFSR with a - * period of 255 as part of the mixing algorithm. Finally, we do - * *not* advance crng_init_cnt since buffer we may get may be something - * like a fixed DMI table (for example), which might very well be - * unique to the machine, but is otherwise unvarying. + * So, we simply hash the contents in with the current key. Finally, + * we do *not* advance crng_init_cnt since buffer we may get may be + * something like a fixed DMI table (for example), which might very + * well be unique to the machine, but is otherwise unvarying. */ -static int crng_slow_load(const u8 *cp, size_t len) +static void crng_slow_load(const u8 *cp, size_t len) { unsigned long flags; - static u8 lfsr = 1; - u8 tmp; - unsigned int i, max = sizeof(base_crng.key); - const u8 *src_buf = cp; - u8 *dest_buf = base_crng.key; + struct blake2s_state hash; + + blake2s_init(&hash, sizeof(base_crng.key));
if (!spin_trylock_irqsave(&base_crng.lock, flags)) - return 0; + return; if (crng_init != 0) { spin_unlock_irqrestore(&base_crng.lock, flags); - return 0; - } - if (len > max) - max = len; - - for (i = 0; i < max; i++) { - tmp = lfsr; - lfsr >>= 1; - if (tmp & 1) - lfsr ^= 0xE1; - tmp = dest_buf[i % sizeof(base_crng.key)]; - dest_buf[i % sizeof(base_crng.key)] ^= src_buf[i % len] ^ lfsr; - lfsr += (tmp << 3) | (tmp >> 5); + return; } + + blake2s_update(&hash, base_crng.key, sizeof(base_crng.key)); + blake2s_update(&hash, cp, len); + blake2s_final(&hash, base_crng.key); + spin_unlock_irqrestore(&base_crng.lock, flags); - return 1; }
static void crng_reseed(void)