prandom: introduce prandom_bytes() and prandom_bytes_state()

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: Eilon Greenstein <eilong@broadcom.com>
Cc: David Laight <david.laight@aculab.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Robert Love <robert.w.love@intel.com>
Cc: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/random32.c b/lib/random32.c
index d1830fade915..52280d5526be 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