random: prime last_data value per fips requirements

The value stored in last_data must be primed for FIPS 140-2 purposes. Upon
first use, either on system startup or after an RNDCLEARPOOL ioctl, we
need to take an initial random sample, store it internally in last_data,
then pass along the value after that to the requester, so that consistency
checks aren't being run against stale and possibly known data.

CC: Herbert Xu <herbert@gondor.apana.org.au>
CC: "David S. Miller" <davem@davemloft.net>
CC: Matt Mackall <mpm@selenic.com>
CC: linux-crypto@vger.kernel.org
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index a1af1839576..85e81ec1451 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -433,6 +433,7 @@ struct entropy_store {
         int entropy_count;
         int entropy_total;
         unsigned int initialized:1;
+        bool last_data_init;
         __u8 last_data[EXTRACT_SIZE];
 };
 
@@ -953,6 +954,10 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
         ssize_t ret = 0, i;
         __u8 tmp[EXTRACT_SIZE];
 
+        /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */
+        if (fips_enabled && !r->last_data_init)
+                nbytes += EXTRACT_SIZE;
+
         trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_);
         xfer_secondary_pool(r, nbytes);
         nbytes = account(r, nbytes, min, reserved);
@@ -963,6 +968,17 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
                 if (fips_enabled) {
                         unsigned long flags;
 
+
+                        /* prime last_data value if need be, per fips 140-2 */
+                        if (!r->last_data_init) {
+                                spin_lock_irqsave(&r->lock, flags);
+                                memcpy(r->last_data, tmp, EXTRACT_SIZE);
+                                r->last_data_init = true;
+                                nbytes -= EXTRACT_SIZE;
+                                spin_unlock_irqrestore(&r->lock, flags);
+                                extract_buf(r, tmp);
+                        }
+
                         spin_lock_irqsave(&r->lock, flags);
                         if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
                                 panic("Hardware RNG duplicated output!\n");
@@ -1082,6 +1098,7 @@ static void init_std_data(struct entropy_store *r)
 
         r->entropy_count = 0;
         r->entropy_total = 0;
+        r->last_data_init = false;
         mix_pool_bytes(r, &now, sizeof(now), NULL);
         for (i = r->poolinfo->POOLBYTES; i > 0; i -= sizeof(rv)) {
                 if (!arch_get_random_long(&rv))