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| author | Eric Biggers <ebiggers@kernel.org> | 2026-04-19 23:34:20 -0700 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2026-05-07 16:10:01 +0800 |
| commit | a918c3680d2ea1d3c2df589397c0ffd4dac2ceaa (patch) | |
| tree | 8fe78e778ca87be9fc69dcb26a5f2237aecdf2bf /crypto | |
| parent | 005b19f18ea9fc51fc35fbcb27759ae83c7c89f8 (diff) | |
| download | linux-next-history-a918c3680d2ea1d3c2df589397c0ffd4dac2ceaa.tar.gz | |
crypto: drbg - Remove redundant reseeding based on random.c state
We're now incorporating 32 bytes from get_random_bytes() in the
additional input string on every request. The additional input string
is processed with a call to drbg_hmac_update(), which is exactly how the
seed is processed. Thus, in reality this is as good as a reseed.
From the perspective of FIPS 140-3, it isn't as good as a reseed. But
it doesn't actually matter, because from FIPS's point of view
get_random_bytes() provides zero entropy anyway.
Thus, neither the reseed with more get_random_bytes() every 300s, nor
the logic that reseeds more frequently before rng_is_initialized(), is
actually needed anymore. Remove it to simplify the code significantly.
(Technically the use of get_random_bytes() in drbg_seed() itself could
be removed too. But it's safer to keep it there for now.)
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto')
| -rw-r--r-- | crypto/drbg.c | 107 |
1 files changed, 9 insertions, 98 deletions
diff --git a/crypto/drbg.c b/crypto/drbg.c index 7fd076ddc1053..bab766026177a 100644 --- a/crypto/drbg.c +++ b/crypto/drbg.c @@ -93,18 +93,11 @@ #include <crypto/sha2.h> #include <linux/fips.h> #include <linux/kernel.h> -#include <linux/jiffies.h> #include <linux/module.h> #include <linux/mutex.h> #include <linux/string_choices.h> #include <linux/unaligned.h> -enum drbg_seed_state { - DRBG_SEED_STATE_UNSEEDED, - DRBG_SEED_STATE_PARTIAL, /* Seeded with !rng_is_initialized() */ - DRBG_SEED_STATE_FULL, -}; - /* State length in bytes */ #define DRBG_STATE_LEN SHA512_DIGEST_SIZE @@ -137,9 +130,6 @@ struct drbg_state { struct hmac_sha512_key key; /* current key -- 10.1.2.1 1b */ /* Number of RNG requests since last reseed -- 10.1.2.1 1c */ size_t reseed_ctr; - size_t reseed_threshold; - enum drbg_seed_state seeded; /* DRBG fully seeded? */ - unsigned long last_seed_time; bool instantiated; bool pr; /* Prediction resistance enabled? */ struct crypto_rng *jent; @@ -239,72 +229,6 @@ static void drbg_hmac_generate(struct drbg_state *drbg, memzero_explicit(addtl2, sizeof(addtl2)); } -static inline void __drbg_seed(struct drbg_state *drbg, - const u8 *seed1, size_t seed1_len, - const u8 *seed2, size_t seed2_len, - enum drbg_seed_state new_seed_state) -{ - drbg_hmac_update(drbg, seed1, seed1_len, seed2, seed2_len); - - drbg->seeded = new_seed_state; - drbg->last_seed_time = jiffies; - drbg->reseed_ctr = 1; - - switch (drbg->seeded) { - case DRBG_SEED_STATE_UNSEEDED: - /* Impossible, but handle it to silence compiler warnings. */ - fallthrough; - case DRBG_SEED_STATE_PARTIAL: - /* - * Require frequent reseeds until the seed source is - * fully initialized. - */ - drbg->reseed_threshold = 50; - break; - - case DRBG_SEED_STATE_FULL: - /* - * Seed source has become fully initialized, frequent - * reseeds no longer required. - */ - drbg->reseed_threshold = DRBG_MAX_REQUESTS; - break; - } -} - -static void drbg_seed_from_random(struct drbg_state *drbg) - __must_hold(&drbg->drbg_mutex) -{ - u8 entropy[DRBG_SEC_STRENGTH]; - - get_random_bytes(entropy, DRBG_SEC_STRENGTH); - - __drbg_seed(drbg, entropy, DRBG_SEC_STRENGTH, NULL, 0, - DRBG_SEED_STATE_FULL); - - memzero_explicit(entropy, DRBG_SEC_STRENGTH); -} - -static bool drbg_nopr_reseed_interval_elapsed(struct drbg_state *drbg) -{ - unsigned long next_reseed; - - /* Don't ever reseed from get_random_bytes() in test mode. */ - if (drbg->test_entropylen) - return false; - - /* - * Obtain fresh entropy for the nopr DRBGs after 300s have - * elapsed in order to still achieve sort of partial - * prediction resistance over the time domain at least. Note - * that the period of 300s has been chosen to match the - * CRNG_RESEED_INTERVAL of the get_random_bytes()' chacha - * rngs. - */ - next_reseed = drbg->last_seed_time + 300 * HZ; - return time_after(jiffies, next_reseed); -} - /* * Seeding or reseeding of the DRBG * @@ -325,7 +249,6 @@ static int drbg_seed(struct drbg_state *drbg, const u8 *pers, size_t pers_len, u8 entropy_buf[(32 + 16) * 2]; size_t entropylen; const u8 *entropy; - enum drbg_seed_state new_seed_state = DRBG_SEED_STATE_FULL; /* 9.1 / 9.2 / 9.3.1 step 3 */ if (pers_len > DRBG_MAX_ADDTL) { @@ -355,9 +278,6 @@ static int drbg_seed(struct drbg_state *drbg, const u8 *pers, size_t pers_len, BUG_ON(entropylen * 2 > sizeof(entropy_buf)); /* Get seed from in-kernel /dev/urandom */ - if (!rng_is_initialized()) - new_seed_state = DRBG_SEED_STATE_PARTIAL; - get_random_bytes(entropy_buf, entropylen); if (!drbg->jent) { @@ -401,7 +321,8 @@ static int drbg_seed(struct drbg_state *drbg, const u8 *pers, size_t pers_len, if (pers_len) pr_devel("DRBG: using personalization string\n"); - __drbg_seed(drbg, entropy, entropylen, pers, pers_len, new_seed_state); + drbg_hmac_update(drbg, entropy, entropylen, pers, pers_len); + drbg->reseed_ctr = 1; ret = 0; out: memzero_explicit(entropy_buf, sizeof(entropy_buf)); @@ -463,16 +384,14 @@ static int drbg_generate(struct drbg_state *drbg, /* * 9.3.1 step 6 and 9 supplemented by 9.3.2 step c is implemented * here. The spec is a bit convoluted here, we make it simpler. + * + * We no longer try to detect when random.c has reseeded itself and call + * drbg_seed() then too, since drbg_hmac_generate() adds bytes from + * random.c to the additional input, which is a de facto reseed anyway. */ - if (drbg->reseed_threshold < drbg->reseed_ctr) - drbg->seeded = DRBG_SEED_STATE_UNSEEDED; - - if (drbg->pr || drbg->seeded == DRBG_SEED_STATE_UNSEEDED) { - pr_devel("DRBG: reseeding before generation (prediction " - "resistance: %s, state %s)\n", - str_true_false(drbg->pr), - (drbg->seeded == DRBG_SEED_STATE_FULL ? - "seeded" : "unseeded")); + if (drbg->pr || drbg->reseed_ctr > DRBG_MAX_REQUESTS) { + pr_devel("DRBG: reseeding before generation (prediction resistance: %s)\n", + str_true_false(drbg->pr)); /* 9.3.1 steps 7.1 through 7.3 */ len = drbg_seed(drbg, addtl, addtl_len, true); if (len) @@ -480,10 +399,6 @@ static int drbg_generate(struct drbg_state *drbg, /* 9.3.1 step 7.4 */ addtl = NULL; addtl_len = 0; - } else if (rng_is_initialized() && - (drbg->seeded == DRBG_SEED_STATE_PARTIAL || - drbg_nopr_reseed_interval_elapsed(drbg))) { - drbg_seed_from_random(drbg); } /* 9.3.1 step 8 and 10 */ @@ -564,9 +479,6 @@ static int drbg_kcapi_seed(struct crypto_rng *tfm, /* 9.1 step 4 is implicit in DRBG_SEC_STRENGTH */ drbg->pr = pr; - drbg->seeded = DRBG_SEED_STATE_UNSEEDED; - drbg->last_seed_time = 0; - drbg->reseed_threshold = DRBG_MAX_REQUESTS; memset(drbg->V, 1, DRBG_STATE_LEN); hmac_sha512_preparekey(&drbg->key, initial_key, DRBG_STATE_LEN); @@ -673,7 +585,6 @@ static inline int __init drbg_healthcheck_sanity(void) guard(mutex_init)(&drbg->drbg_mutex); drbg->instantiated = true; - drbg->reseed_threshold = DRBG_MAX_REQUESTS; /* * if the following tests fail, it is likely that there is a buffer |