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-rw-r--r--drivers/char/random.c122
1 files changed, 70 insertions, 52 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index e83f645..a93ea7e 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -840,51 +840,64 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
size_t nbytes, int min, int rsvd);
/*
- * This utility inline function is responsible for transferring entropy
- * from the primary pool to the secondary extraction pool. We make
- * sure we pull enough for a 'catastrophic reseed'.
+ * This function is responsible for filling this pool (r)
+ * to an appropriate level, by pulling from the upstream
+ * pool (r->pull), if any, if necessary.
+ *
+ * We enforce (probably redundantly) the requirement that
+ * any pull be large enough to be "significant" to any attacker.
+ *
+ * In principle, this would cascade, pulling from other pools
+ * even farther upstream, but as it stands there are only two
+ * pools, so no cascade.
*/
-static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
-{
+static void fill_pool(
+ struct entropy_store *r,
+ size_t want_level /* measured in bytes */
+){
__u32 tmp[OUTPUT_POOL_WORDS];
-
- if (!r->pull) return;
- if (r->entropy_count < nbytes * 8 && r->entropy_count < r->poolinfo->POOLBITS) {
- int rsvd = 0;
- int bytes = nbytes;
- if (!r->limit) {
+ int rsvd = 0; /* measured in bits */
+ int actual; /* measured in BYTES */
+ int txbits = BYTE2BIT(want_level) - r->entropy_count;
+ if (txbits < 0) return; /* already have enough */
+ if (r->entropy_count >= r->poolinfo->POOLBITS) return; /* already full */
+ if (!r->pull) return; /* no upstream pool to pull from */
+ if (!r->limit) {
/*
- * Here if we are non-limited i.e. non-blocking i.e. urandom.
- * Reserve a suitable amount of entropy in the input pool,
- * based on how desperate we are to be reseeded.
- *
- * The dilution factor ranges from 819 to 1 (at appetite=0)
- * to 858,993,459 to 1 (at appetite=20)
- */
- int appetite = fls64(r->extracted_subttl) - 18;
- if (appetite < 0) return; /* 128k bits maps to appetite 0 */
-/* Max possible rsvd: */
- rsvd = W2BIT(r->pull->poolinfo->poolwords) - RESEED_BATCH;
+* Here if we are non-limited i.e. non-blocking i.e. urandom.
+* Reserve a suitable amount of entropy in the input pool, a
+* sliding scale based on how desperately we need to be reseeded.
+*
+* The dilution factor ranges from 819 to 1 (at appetite=0)
+* to 858,993,459 to 1 (at appetite=20)
+*/
+ int appetite = fls64(r->extracted_subttl) - 18;
+ if (appetite < 0) return; /* 128k bits maps to appetite 0 */
+/* The largest rsvd that makes any sense: */
+ rsvd = W2BIT(r->pull->poolinfo->poolwords) - RESEED_BATCH;
/* When the appetite gets to 20, rsvd goes to zero: */
- rsvd = rsvd - appetite*rsvd/20;
- if (rsvd < 0) rsvd = 0;
- }
-
- /* Make the request big enough to be "significant" to any attacker: */
- bytes = max_t(int, bytes, BIT2BYTE(RESEED_BATCH));
- /* but never more than our buffer size */
- bytes = min_t(int, bytes, sizeof(tmp));
-
- DEBUG_ENT("Going to reseed %s with %d bits; "
- "caller requested: %zu prev level: %d\n",
- r->name, bytes * 8, nbytes * 8, r->entropy_count);
-
- bytes = extract_entropy(r->pull, tmp, bytes,
- BIT2BYTE(RESEED_BATCH), BIT2BYTE(rsvd));
- mix_pool_bytes(r, tmp, bytes, NULL);
- credit_entropy_bits(r, bytes*8);
- }
-// FIXME: return bytes;
+ rsvd = rsvd - appetite*rsvd/20;
+ if (rsvd < 0) rsvd = 0;
+ }
+
+ /* Make the request big enough to be "significant" to any attacker: */
+ txbits = max_t(int, txbits, RESEED_BATCH);
+ /* but never more than our buffer size */
+ txbits = min_t(int, txbits, 8*sizeof(tmp));
+
+ DEBUG_ENT("Going to reseed %s with %d bits; "
+ "caller want_level: %zu prev level: %d\n",
+ r->name, txbits,
+ want_level * 8, r->entropy_count);
+
+ actual = extract_entropy(r->pull, tmp, BIT2BYTE(txbits),
+ BIT2BYTE(RESEED_BATCH), BIT2BYTE(rsvd));
+ mix_pool_bytes(r, tmp, actual, NULL);
+ credit_entropy_bits(r, actual*8);
+ if (BYTE2BIT(actual) > RESEED_BATCH) {
+ r->extracted_subttl = 0;
+ }
+// FIXME: return actual;
}
/*
@@ -1012,8 +1025,9 @@ static void extract_buf(struct entropy_store *r, __u8 *out)
memset(&hash, 0, sizeof(hash));
}
+/* returns actual number of bytes extracted */
static ssize_t extract_entropy(struct entropy_store *r, void *buf,
- size_t nbytes, int min, int reserved)
+ size_t txbytes, int min, int reserved)
{
ssize_t ret = 0, i;
__u8 tmp[EXTRACT_SIZE];
@@ -1027,7 +1041,7 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
spin_unlock_irqrestore(&r->lock, flags);
trace_extract_entropy(r->name, EXTRACT_SIZE,
r->entropy_count, _RET_IP_);
- xfer_secondary_pool(r, EXTRACT_SIZE);
+ fill_pool(r, EXTRACT_SIZE);
extract_buf(r, tmp);
spin_lock_irqsave(&r->lock, flags);
memcpy(r->last_data, tmp, EXTRACT_SIZE);
@@ -1035,11 +1049,15 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
spin_unlock_irqrestore(&r->lock, flags);
}
- trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
- xfer_secondary_pool(r, nbytes);
- nbytes = account(r, nbytes, min, reserved);
+ trace_extract_entropy(r->name, txbytes, r->entropy_count, _RET_IP_);
+/* We want our pool (r) to have enough, if possible.
+ * So pull it up to a level (txbits) that will cover the
+ * extraction we are about to do.
+ */
+ fill_pool(r, txbytes);
+ txbytes = account(r, txbytes, min, reserved);
- while (nbytes) {
+ while (txbytes) {
extract_buf(r, tmp);
if (fips_enabled) {
@@ -1049,9 +1067,9 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
memcpy(r->last_data, tmp, EXTRACT_SIZE);
spin_unlock_irqrestore(&r->lock, flags);
}
- i = min_t(int, nbytes, EXTRACT_SIZE);
+ i = min_t(int, txbytes, EXTRACT_SIZE);
memcpy(buf, tmp, i);
- nbytes -= i;
+ txbytes -= i;
buf += i;
ret += i;
}
@@ -1060,11 +1078,11 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
memset(tmp, 0, sizeof(tmp));
if (ret > 0) {
-/* Prevent overflow; saturate at a user-friendly round number: */
+/* Subttl does not overflow; it saturates at a user-friendly round number: */
r->extracted_subttl += BYTE2BIT(ret);
if (r->extracted_subttl > 1000000000000000000LL) r->extracted_subttl = 1000000000000000000LL;
+/* Total does not saturate; it just overflows and wraps around. */
r->extracted_total += BYTE2BIT(ret);
- if (r->extracted_total > 1000000000000000000LL) r->extracted_total = 1000000000000000000LL;
}
return ret;
}
@@ -1076,7 +1094,7 @@ static ssize_t extract_entropy_user(struct entropy_store *r, void __user *buf,
__u8 tmp[EXTRACT_SIZE];
trace_extract_entropy_user(r->name, nbytes, r->entropy_count, _RET_IP_);
- xfer_secondary_pool(r, nbytes);
+ fill_pool(r, nbytes);
nbytes = account(r, nbytes, 0, 0);
while (nbytes) {
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-26 19:01:12 +0000