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crypto: drbg - make reseeding from get_random_bytes() synchronous 

commit 074bcd4000 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 16b369a91d ("random: Blocking API for accessing
                        nonblocking_pool")
  commit 4c7879907e ("crypto: drbg - add async seeding operation")

  commit 205a525c33 ("random: Add callback API for random pool
                        readiness")
  commit 57225e6797 ("crypto: drbg - Use callback API for random
                        readiness")
  commit c2719503f5 ("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
9a47249d44 ("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>
This commit is contained in:
Nicolai Stange 2022-06-02 22:22:32 +02:00 committed by Greg Kroah-Hartman
parent ba6a98f8c7
commit ab62f0f9d3
3 changed files with 11 additions and 54 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
crypto/drbg.c
View File

@ -1087,12 +1087,10 @@ static inline int drbg_get_random_bytes(struct drbg_state *drbg,
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;
@ -1103,23 +1101,15 @@ static void drbg_async_seed(struct work_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;
goto out;
/* Reset ->seeded so that if __drbg_seed fails the next
* generate call will trigger a reseed.
*/
drbg->seeded = DRBG_SEED_STATE_UNSEEDED;
__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;
}
/*
@ -1420,6 +1410,11 @@ static int drbg_generate(struct drbg_state *drbg,
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)
@ -1512,44 +1507,15 @@ static int drbg_generate_long(struct drbg_state *drbg,
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;
}
/*
@ -1643,11 +1609,6 @@ 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;

2
drivers/char/random.c
View File

@ -158,7 +158,6 @@ int __cold register_random_ready_notifier(struct notifier_block *nb)
spin_unlock_irqrestore(&random_ready_chain_lock, flags);
return ret;
}
EXPORT_SYMBOL(register_random_ready_notifier);
/*
* Delete a previously registered readiness callback function.
@ -173,7 +172,6 @@ int __cold unregister_random_ready_notifier(struct notifier_block *nb)
spin_unlock_irqrestore(&random_ready_chain_lock, flags);
return ret;
}
EXPORT_SYMBOL(unregister_random_ready_notifier);
static void __cold process_random_ready_list(void)
{

2
include/crypto/drbg.h
View File

@ -139,12 +139,10 @@ 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)