From a98406e22c12e514bac28fec0a49dc793edaf3a8 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Sat, 23 Aug 2014 17:03:28 +0200 Subject: random32: improvements to prandom_bytes MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This patch addresses a couple of minor items, mostly addesssing prandom_bytes(): 1) prandom_bytes{,_state}() should use size_t for length arguments, 2) We can use put_unaligned() when filling the array instead of open coding it [ perhaps some archs will further benefit from their own arch specific implementation when GCC cannot make up for it ], 3) Fix a typo, 4) Better use unsigned int as type for getting the arch seed, 5) Make use of prandom_u32_max() for timer slack. Regarding the change to put_unaligned(), callers of prandom_bytes() which internally invoke prandom_bytes_state(), don't bother as they expect the array to be filled randomly and don't have any control of the internal state what-so-ever (that's also why we have periodic reseeding there, etc), so they really don't care. Now for the direct callers of prandom_bytes_state(), which are solely located in test cases for MTD devices, that is, drivers/mtd/tests/{oobtest.c,pagetest.c,subpagetest.c}: These tests basically fill a test write-vector through prandom_bytes_state() with an a-priori defined seed each time and write that to a MTD device. Later on, they set up a read-vector and read back that blocks from the device. So in the verification phase, the write-vector is being re-setup [ so same seed and prandom_bytes_state() called ], and then memcmp()'ed against the read-vector to check if the data is the same. Akinobu, Lothar and I also tested this patch and it runs through the 3 relevant MTD test cases w/o any errors on the nandsim device (simulator for MTD devs) for x86_64, ppc64, ARM (i.MX28, i.MX53 and i.MX6): # modprobe nandsim first_id_byte=0x20 second_id_byte=0xac \ third_id_byte=0x00 fourth_id_byte=0x15 # modprobe mtd_oobtest dev=0 # modprobe mtd_pagetest dev=0 # modprobe mtd_subpagetest dev=0 We also don't have any users depending directly on a particular result of the PRNG (except the PRNG self-test itself), and that's just fine as it e.g. allowed us easily to do things like upgrading from taus88 to taus113. Signed-off-by: Daniel Borkmann Tested-by: Akinobu Mita Tested-by: Lothar Waßmann Cc: Hannes Frederic Sowa Signed-off-by: David S. Miller --- lib/random32.c | 39 ++++++++++++++++++--------------------- 1 file changed, 18 insertions(+), 21 deletions(-) (limited to 'lib/random32.c') diff --git a/lib/random32.c b/lib/random32.c index c9b6bf3afe0c..0bee183fa18f 100644 --- a/lib/random32.c +++ b/lib/random32.c @@ -37,6 +37,7 @@ #include #include #include +#include #ifdef CONFIG_RANDOM32_SELFTEST static void __init prandom_state_selftest(void); @@ -96,27 +97,23 @@ EXPORT_SYMBOL(prandom_u32); * 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) +void prandom_bytes_state(struct rnd_state *state, void *buf, size_t 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; + u8 *ptr = buf; - for (j = 0; j < sizeof(u32); j++) { - p[i + j] = random; - random >>= BITS_PER_BYTE; - } + while (bytes >= sizeof(u32)) { + put_unaligned(prandom_u32_state(state), (u32 *) ptr); + ptr += sizeof(u32); + bytes -= sizeof(u32); } - if (i < bytes) { - u32 random = prandom_u32_state(state); - for (; i < bytes; i++) { - p[i] = random; - random >>= BITS_PER_BYTE; - } + if (bytes > 0) { + u32 rem = prandom_u32_state(state); + do { + *ptr++ = (u8) rem; + bytes--; + rem >>= BITS_PER_BYTE; + } while (bytes > 0); } } EXPORT_SYMBOL(prandom_bytes_state); @@ -126,7 +123,7 @@ EXPORT_SYMBOL(prandom_bytes_state); * @buf: where to copy the pseudo-random bytes to * @bytes: the requested number of bytes */ -void prandom_bytes(void *buf, int bytes) +void prandom_bytes(void *buf, size_t bytes) { struct rnd_state *state = &get_cpu_var(net_rand_state); @@ -137,7 +134,7 @@ EXPORT_SYMBOL(prandom_bytes); static void prandom_warmup(struct rnd_state *state) { - /* Calling RNG ten times to satify recurrence condition */ + /* Calling RNG ten times to satisfy recurrence condition */ prandom_u32_state(state); prandom_u32_state(state); prandom_u32_state(state); @@ -152,7 +149,7 @@ static void prandom_warmup(struct rnd_state *state) static u32 __extract_hwseed(void) { - u32 val = 0; + unsigned int val = 0; (void)(arch_get_random_seed_int(&val) || arch_get_random_int(&val)); @@ -228,7 +225,7 @@ static void __prandom_timer(unsigned long dontcare) prandom_seed(entropy); /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ - expires = 40 + (prandom_u32() % 40); + expires = 40 + prandom_u32_max(40); seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC); add_timer(&seed_timer); -- cgit v1.2.3