From 074bcd4000e0d812bc253f86fedc40f81ed59ccc Mon Sep 17 00:00:00 2001 From: Nicolai Stange Date: Mon, 15 Nov 2021 15:18:07 +0100 Subject: crypto: drbg - make reseeding from get_random_bytes() synchronous 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 Signed-off-by: Herbert Xu --- crypto/drbg.c | 62 +++++++++++------------------------------------------------ 1 file changed, 11 insertions(+), 51 deletions(-) (limited to 'crypto') diff --git a/crypto/drbg.c b/crypto/drbg.c index 9b233e86a5f0..2b03a05a9e99 100644 --- a/crypto/drbg.c +++ b/crypto/drbg.c @@ -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; - - /* 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); + goto out; -unlock: - mutex_unlock(&drbg->drbg_mutex); + ret = __drbg_seed(drbg, &seedlist, true, DRBG_SEED_STATE_FULL); +out: memzero_explicit(entropy, entropylen); + return ret; } /* @@ -1422,6 +1412,11 @@ 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) @@ -1514,45 +1509,15 @@ static int drbg_generate_long(struct drbg_state *drbg, return 0; } -static void drbg_schedule_async_seed(struct random_ready_callback *rdy) -{ - struct drbg_state *drbg = container_of(rdy, struct drbg_state, - random_ready); - - schedule_work(&drbg->seed_work); -} - 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.owner = THIS_MODULE; - drbg->random_ready.func = drbg_schedule_async_seed; - - err = add_random_ready_callback(&drbg->random_ready); - - switch (err) { - case 0: - break; - - case -EALREADY: - err = 0; - fallthrough; - - default: - drbg->random_ready.func = NULL; - return err; - } - - return err; + return 0; } /* @@ -1646,11 +1611,6 @@ free_everything: */ static int drbg_uninstantiate(struct drbg_state *drbg) { - if (drbg->random_ready.func) { - del_random_ready_callback(&drbg->random_ready); - cancel_work_sync(&drbg->seed_work); - } - if (!IS_ERR_OR_NULL(drbg->jent)) crypto_free_rng(drbg->jent); drbg->jent = NULL; -- cgit v1.2.3-70-g09d2