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random: use hash function for crng_slow_load()

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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>
This commit is contained in:
Jason A. Donenfeld
2022-02-08 19:23:17 +01:00
committed by Greg Kroah-Hartman
parent 1f9cc6d2c6
commit 08b7063879
4 changed files with 112 additions and 140 deletions
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10
include/linux/random.h
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@@ -20,8 +20,8 @@ struct random_ready_callback {
struct module *owner;
};
extern void add_device_randomness(const void *, unsigned int);
extern void add_bootloader_randomness(const void *, unsigned int);
extern void add_device_randomness(const void *, size_t);
extern void add_bootloader_randomness(const void *, size_t);
#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
static inline void add_latent_entropy(void)
@@ -37,13 +37,13 @@ extern void add_input_randomness(unsigned int type, unsigned int code,
unsigned int value) __latent_entropy;
extern void add_interrupt_randomness(int irq) __latent_entropy;
extern void get_random_bytes(void *buf, int nbytes);
extern void get_random_bytes(void *buf, size_t nbytes);
extern int wait_for_random_bytes(void);
extern int __init rand_initialize(void);
extern bool rng_is_initialized(void);
extern int add_random_ready_callback(struct random_ready_callback *rdy);
extern void del_random_ready_callback(struct random_ready_callback *rdy);
extern int __must_check get_random_bytes_arch(void *buf, int nbytes);
extern size_t __must_check get_random_bytes_arch(void *buf, size_t nbytes);
#ifndef MODULE
extern const struct file_operations random_fops, urandom_fops;
@@ -87,7 +87,7 @@ static inline unsigned long get_random_canary(void)
/* Calls wait_for_random_bytes() and then calls get_random_bytes(buf, nbytes).
* Returns the result of the call to wait_for_random_bytes. */
static inline int get_random_bytes_wait(void *buf, int nbytes)
static inline int get_random_bytes_wait(void *buf, size_t nbytes)
{
int ret = wait_for_random_bytes();
get_random_bytes(buf, nbytes);