[PATCH v3 02/11] prandom: introduce prandom_bytes() and prandom_bytes_state()

Akinobu Mita
2012-11-13T13:37:44Z

Add functions to get the requested number of pseudo-random bytes.

The difference from get_random_bytes() is that it generates pseudo-random
numbers by prandom_u32(). It doesn't consume the entropy pool, and the
sequence is reproducible if the same rnd_state is used. So it is suitable
for generating random bytes for testing.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: linux-mtd@lists.infradead.org
Cc: Eilon Greenstein <eilong@broadcom.com>
Cc: netdev@vger.kernel.org
---
* v3
- rename random32_get_bytes_state to prandom_bytes_state
- ensure prandom_bytes_state() generates same bytes with same rnd_state

* v2
- rename prandom32_get_bytes to random32_get_bytes_state

include/linux/random.h | 2 ++
lib/random32.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+)

diff --git a/include/linux/random.h b/include/linux/random.h
index db6debc..d984608 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -26,6 +26,7 @@ unsigned int get_random_int(void);
unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);

u32 prandom_u32(void);
+void prandom_bytes(void *buf, int nbytes);
void prandom_seed(u32 seed);

/*
@@ -36,6 +37,7 @@ void prandom_seed(u32 seed);
#define srandom32(seed) prandom_seed(seed)

u32 prandom_u32_state(struct rnd_state *);
+void prandom_bytes_state(struct rnd_state *state, void *buf, int nbytes);

/*
* Handle minimum values for seeds
diff --git a/lib/random32.c b/lib/random32.c
index d1830fa..52280d5 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -77,6 +77,55 @@ u32 prandom_u32(void)
}
EXPORT_SYMBOL(prandom_u32);

+/*
+ * prandom_bytes_state - get the requested number of pseudo-random bytes
+ *
+ * @state: pointer to state structure holding seeded state.
+ * @buf: where to copy the pseudo-random bytes to
+ * @bytes: the requested number of bytes
+ *
+ * This is used for pseudo-randomness with no outside seeding.
+ * For more random results, use prandom_bytes().
+ */
+void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
+{
+ unsigned char *p = buf;
+ int i;
+
+ for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
+ u32 random = prandom_u32_state(state);
+ int j;
+
+ for (j = 0; j < sizeof(u32); j++) {
+ p[i + j] = random;
+ random >>= BITS_PER_BYTE;
+ }
+ }
+ if (i < bytes) {
+ u32 random = prandom_u32_state(state);
+
+ for (; i < bytes; i++) {
+ p[i] = random;
+ random >>= BITS_PER_BYTE;
+ }
+ }
+}
+EXPORT_SYMBOL(prandom_bytes_state);
+
+/**
+ * prandom_bytes - get the requested number of pseudo-random bytes
+ * @buf: where to copy the pseudo-random bytes to
+ * @bytes: the requested number of bytes
+ */
+void prandom_bytes(void *buf, int bytes)
+{
+ struct rnd_state *state = &get_cpu_var(net_rand_state);
+
+ prandom_bytes_state(state, buf, bytes);
+ put_cpu_var(state);
+}
+EXPORT_SYMBOL(prandom_bytes);
+
/**
* prandom_seed - add entropy to pseudo random number generator
* @seed: seed value
--
1.7.11.7