From: Nicolai Stange nstange@suse.de
commit 074bcd4000e0d812bc253f86fedc40f81ed59ccc upstream.
get_random_bytes() usually hasn't full entropy available by the time DRBG instances are first getting seeded from it during boot. Thus, the DRBG implementation registers random_ready_callbacks which would in turn schedule some work for reseeding the DRBGs once get_random_bytes() has sufficient entropy available.
For reference, the relevant history around handling DRBG (re)seeding in the context of a not yet fully seeded get_random_bytes() is:
commit 16b369a91d0d ("random: Blocking API for accessing nonblocking_pool") commit 4c7879907edd ("crypto: drbg - add async seeding operation")
commit 205a525c3342 ("random: Add callback API for random pool readiness") commit 57225e679788 ("crypto: drbg - Use callback API for random readiness") commit c2719503f5e1 ("random: Remove kernel blocking API")
However, some time later, the initialization state of get_random_bytes() has been made queryable via rng_is_initialized() introduced with commit 9a47249d444d ("random: Make crng state queryable"). This primitive now allows for streamlining the DRBG reseeding from get_random_bytes() by replacing that aforementioned asynchronous work scheduling from random_ready_callbacks with some simpler, synchronous code in drbg_generate() next to the related logic already present therein. Apart from improving overall code readability, this change will also enable DRBG users to rely on wait_for_random_bytes() for ensuring that the initial seeding has completed, if desired.
The previous patches already laid the grounds by making drbg_seed() to record at each DRBG instance whether it was being seeded at a time when rng_is_initialized() still had been false as indicated by ->seeded == DRBG_SEED_STATE_PARTIAL.
All that remains to be done now is to make drbg_generate() check for this condition, determine whether rng_is_initialized() has flipped to true in the meanwhile and invoke a reseed from get_random_bytes() if so.
Make this move: - rename the former drbg_async_seed() work handler, i.e. the one in charge of reseeding a DRBG instance from get_random_bytes(), to "drbg_seed_from_random()", - change its signature as appropriate, i.e. make it take a struct drbg_state rather than a work_struct and change its return type from "void" to "int" in order to allow for passing error information from e.g. its __drbg_seed() invocation onwards to callers, - make drbg_generate() invoke this drbg_seed_from_random() once it encounters a DRBG instance with ->seeded == DRBG_SEED_STATE_PARTIAL by the time rng_is_initialized() has flipped to true and - prune everything related to the former, random_ready_callback based mechanism.
As drbg_seed_from_random() is now getting invoked from drbg_generate() with the ->drbg_mutex being held, it must not attempt to recursively grab it once again. Remove the corresponding mutex operations from what is now drbg_seed_from_random(). Furthermore, as drbg_seed_from_random() can now report errors directly to its caller, there's no need for it to temporarily switch the DRBG's ->seeded state to DRBG_SEED_STATE_UNSEEDED so that a failure of the subsequently invoked __drbg_seed() will get signaled to drbg_generate(). Don't do it then.
Signed-off-by: Nicolai Stange nstange@suse.de Signed-off-by: Herbert Xu herbert@gondor.apana.org.au [Jason: for stable, undid the modifications for the backport of 5acd3548.] Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- crypto/drbg.c | 61 +++++++++----------------------------------------- drivers/char/random.c | 2 - include/crypto/drbg.h | 2 - 3 files changed, 11 insertions(+), 54 deletions(-)
--- a/crypto/drbg.c +++ b/crypto/drbg.c @@ -1085,12 +1085,10 @@ static inline int drbg_get_random_bytes( return 0; }
-static void drbg_async_seed(struct work_struct *work) +static int drbg_seed_from_random(struct drbg_state *drbg) { struct drbg_string data; LIST_HEAD(seedlist); - struct drbg_state *drbg = container_of(work, struct drbg_state, - seed_work); unsigned int entropylen = drbg_sec_strength(drbg->core->flags); unsigned char entropy[32]; int ret; @@ -1101,23 +1099,15 @@ static void drbg_async_seed(struct work_ drbg_string_fill(&data, entropy, entropylen); list_add_tail(&data.list, &seedlist);
- mutex_lock(&drbg->drbg_mutex); - ret = drbg_get_random_bytes(drbg, entropy, entropylen); if (ret) - goto unlock; - - /* Reset ->seeded so that if __drbg_seed fails the next - * generate call will trigger a reseed. - */ - drbg->seeded = DRBG_SEED_STATE_UNSEEDED; + goto out;
- __drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL); - -unlock: - mutex_unlock(&drbg->drbg_mutex); + ret = __drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL);
+out: memzero_explicit(entropy, entropylen); + return ret; }
/* @@ -1418,6 +1408,11 @@ static int drbg_generate(struct drbg_sta goto err; /* 9.3.1 step 7.4 */ addtl = NULL; + } else if (rng_is_initialized() && + drbg->seeded == DRBG_SEED_STATE_PARTIAL) { + len = drbg_seed_from_random(drbg); + if (len) + goto err; }
if (addtl && 0 < addtl->len) @@ -1510,44 +1505,15 @@ static int drbg_generate_long(struct drb return 0; }
-static int drbg_schedule_async_seed(struct notifier_block *nb, unsigned long action, void *data) -{ - struct drbg_state *drbg = container_of(nb, struct drbg_state, - random_ready); - - schedule_work(&drbg->seed_work); - return 0; -} - static int drbg_prepare_hrng(struct drbg_state *drbg) { - int err; - /* We do not need an HRNG in test mode. */ if (list_empty(&drbg->test_data.list)) return 0;
drbg->jent = crypto_alloc_rng("jitterentropy_rng", 0, 0);
- INIT_WORK(&drbg->seed_work, drbg_async_seed); - - drbg->random_ready.notifier_call = drbg_schedule_async_seed; - err = register_random_ready_notifier(&drbg->random_ready); - - switch (err) { - case 0: - break; - - case -EALREADY: - err = 0; - /* fall through */ - - default: - drbg->random_ready.notifier_call = NULL; - return err; - } - - return err; + return 0; }
/* @@ -1641,11 +1607,6 @@ free_everything: */ static int drbg_uninstantiate(struct drbg_state *drbg) { - if (drbg->random_ready.notifier_call) { - unregister_random_ready_notifier(&drbg->random_ready); - cancel_work_sync(&drbg->seed_work); - } - if (!IS_ERR_OR_NULL(drbg->jent)) crypto_free_rng(drbg->jent); drbg->jent = NULL; --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -157,7 +157,6 @@ int __cold register_random_ready_notifie spin_unlock_irqrestore(&random_ready_chain_lock, flags); return ret; } -EXPORT_SYMBOL(register_random_ready_notifier);
/* * Delete a previously registered readiness callback function. @@ -172,7 +171,6 @@ int __cold unregister_random_ready_notif spin_unlock_irqrestore(&random_ready_chain_lock, flags); return ret; } -EXPORT_SYMBOL(unregister_random_ready_notifier);
static void __cold process_random_ready_list(void) { --- a/include/crypto/drbg.h +++ b/include/crypto/drbg.h @@ -137,12 +137,10 @@ struct drbg_state { bool pr; /* Prediction resistance enabled? */ bool fips_primed; /* Continuous test primed? */ unsigned char *prev; /* FIPS 140-2 continuous test value */ - struct work_struct seed_work; /* asynchronous seeding support */ struct crypto_rng *jent; const struct drbg_state_ops *d_ops; const struct drbg_core *core; struct drbg_string test_data; - struct notifier_block random_ready; };
static inline __u8 drbg_statelen(struct drbg_state *drbg)