During initialization, the DRBG now tries to allocate a handle of the
Jitter RNG. If such a Jitter RNG is available during seeding, the DRBG
pulls the required entropy/nonce string from get_random_bytes and
concatenates it with a string of equal size from the Jitter RNG. That
combined string is now the seed for the DRBG.
Written differently, the initial seed of the DRBG is now:
get_random_bytes(entropy/nonce) || jitterentropy (entropy/nonce)
If the Jitter RNG is not available, the DRBG only seeds from
get_random_bytes.
CC: Andreas Steffen <andreas.stef...@strongswan.org>
CC: Theodore Ts'o <ty...@mit.edu>
CC: Sandy Harris <sandyinch...@gmail.com>
Signed-off-by: Stephan Mueller <smuel...@chronox.de>
---
crypto/drbg.c | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
include/crypto/drbg.h | 1 +
2 files changed, 45 insertions(+), 7 deletions(-)
diff --git a/crypto/drbg.c b/crypto/drbg.c
index 563e5e9..e9fd60d 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -1072,7 +1072,11 @@ static void drbg_async_seed(struct work_struct *work)
drbg_string_fill(&data, drbg->seed_buf, drbg->seed_buf_len);
list_add_tail(&data.list, &seedlist);
mutex_lock(&drbg->drbg_mutex);
- __drbg_seed(drbg, &seedlist, true);
+ ret = __drbg_seed(drbg, &seedlist, true);
+ if (!ret && drbg->jent) {
+ crypto_free_rng(drbg->jent);
+ drbg->jent = NULL;
+ }
memzero_explicit(drbg->seed_buf, drbg->seed_buf_len);
mutex_unlock(&drbg->drbg_mutex);
}
@@ -1107,10 +1111,24 @@ static int drbg_seed(struct drbg_state *drbg, struct
drbg_string *pers,
drbg->test_data.len);
pr_devel("DRBG: using test entropy\n");
} else {
- pr_devel("DRBG: (re)seeding with %zu bytes of entropy\n",
- drbg->seed_buf_len);
+ /* Get seed from in-kernel /dev/urandom */
get_random_bytes(drbg->seed_buf, drbg->seed_buf_len);
- drbg_string_fill(&data1, drbg->seed_buf, drbg->seed_buf_len);
+
+ /* Get seed from Jitter RNG */
+ if (!drbg->jent ||
+ crypto_rng_get_bytes(drbg->jent,
+ drbg->seed_buf + drbg->seed_buf_len,
+ drbg->seed_buf_len)) {
+ drbg_string_fill(&data1, drbg->seed_buf,
+ drbg->seed_buf_len);
+ pr_devel("DRBG: (re)seeding with %zu bytes of
entropy\n",
+ drbg->seed_buf_len);
+ } else {
+ drbg_string_fill(&data1, drbg->seed_buf,
+ drbg->seed_buf_len * 2);
+ pr_devel("DRBG: (re)seeding with %zu bytes of
entropy\n",
+ drbg->seed_buf_len * 2);
+ }
}
list_add_tail(&data1.list, &seedlist);
@@ -1135,7 +1153,7 @@ static int drbg_seed(struct drbg_state *drbg, struct
drbg_string *pers,
* Clear the initial entropy buffer as the async call may not overwrite
* that buffer for quite some time.
*/
- memzero_explicit(drbg->seed_buf, drbg->seed_buf_len);
+ memzero_explicit(drbg->seed_buf, drbg->seed_buf_len * 2);
if (ret)
goto out;
/*
@@ -1175,6 +1193,10 @@ static inline void drbg_dealloc_state(struct drbg_state
*drbg)
#endif
kzfree(drbg->seed_buf);
drbg->seed_buf = NULL;
+ if (drbg->jent) {
+ crypto_free_rng(drbg->jent);
+ drbg->jent = NULL;
+ }
}
/*
@@ -1250,14 +1272,29 @@ static inline int drbg_alloc_state(struct drbg_state
*drbg)
ret = -EFAULT;
goto err;
}
- /* ensure we have sufficient buffer space for initial seed */
+ /*
+ * Ensure we have sufficient buffer space for initial seed which
+ * consists of the seed from get_random_bytes and the Jitter RNG.
+ */
drbg->seed_buf_len = ((drbg->seed_buf_len + 1) / 2) * 3;
- drbg->seed_buf = kzalloc(drbg->seed_buf_len, GFP_KERNEL);
+ drbg->seed_buf = kzalloc(drbg->seed_buf_len * 2, GFP_KERNEL);
if (!drbg->seed_buf)
goto err;
INIT_WORK(&drbg->seed_work, drbg_async_seed);
+ drbg->jent = crypto_alloc_rng("jitterentropy_rng", 0, 0);
+ if(IS_ERR(drbg->jent))
+ {
+ pr_info("DRBG: could not allocate Jitter RNG handle for
seeding\n");
+ /*
+ * As the Jitter RNG is a module that may not be present, we
+ * continue with the operation and do not fully tie the DRBG
+ * to the Jitter RNG.
+ */
+ drbg->jent = NULL;
+ }
+
return 0;
err:
diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index 46994b2..c3f208d 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -123,6 +123,7 @@ struct drbg_state {
struct work_struct seed_work; /* asynchronous seeding support */
u8 *seed_buf; /* buffer holding the seed */
size_t seed_buf_len;
+ struct crypto_rng *jent;
const struct drbg_state_ops *d_ops;
const struct drbg_core *core;
struct drbg_string test_data;
--
2.1.0
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