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![Neil Horman](/assets/img/avatar_default.png)
Pseudo RNGs provide predictable outputs based on input parateters {key, V, DT}, the idea behind them is that only the user should know what the inputs are. While its nice to have default known values for testing purposes, it seems dangerous to allow the use of those default values without some sort of safety measure in place, lest an attacker easily guess the output of the cprng. This patch forces the NEED_RESET flag on when allocating a cprng context, so that any user is forced to reseed it before use. The defaults can still be used for testing, but this will prevent their inadvertent use, and be more secure. Signed-off-by: Neil Horman <nhorman@redhat.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
441 lines
9.7 KiB
C
441 lines
9.7 KiB
C
/*
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* PRNG: Pseudo Random Number Generator
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* Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using
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* AES 128 cipher
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*
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* (C) Neil Horman <nhorman@tuxdriver.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License as published by the
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* Free Software Foundation; either version 2 of the License, or (at your
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* any later version.
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*
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*
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*/
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#include <crypto/internal/rng.h>
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#include <linux/err.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/string.h>
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#include "internal.h"
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#define DEFAULT_PRNG_KEY "0123456789abcdef"
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#define DEFAULT_PRNG_KSZ 16
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#define DEFAULT_BLK_SZ 16
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#define DEFAULT_V_SEED "zaybxcwdveuftgsh"
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/*
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* Flags for the prng_context flags field
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*/
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#define PRNG_FIXED_SIZE 0x1
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#define PRNG_NEED_RESET 0x2
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/*
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* Note: DT is our counter value
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* I is our intermediate value
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* V is our seed vector
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* See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf
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* for implementation details
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*/
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struct prng_context {
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spinlock_t prng_lock;
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unsigned char rand_data[DEFAULT_BLK_SZ];
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unsigned char last_rand_data[DEFAULT_BLK_SZ];
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unsigned char DT[DEFAULT_BLK_SZ];
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unsigned char I[DEFAULT_BLK_SZ];
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unsigned char V[DEFAULT_BLK_SZ];
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u32 rand_data_valid;
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struct crypto_cipher *tfm;
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u32 flags;
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};
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static int dbg;
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static void hexdump(char *note, unsigned char *buf, unsigned int len)
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{
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if (dbg) {
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printk(KERN_CRIT "%s", note);
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print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET,
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16, 1,
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buf, len, false);
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}
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}
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#define dbgprint(format, args...) do {\
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if (dbg)\
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printk(format, ##args);\
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} while (0)
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static void xor_vectors(unsigned char *in1, unsigned char *in2,
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unsigned char *out, unsigned int size)
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{
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int i;
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for (i = 0; i < size; i++)
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out[i] = in1[i] ^ in2[i];
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}
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/*
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* Returns DEFAULT_BLK_SZ bytes of random data per call
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* returns 0 if generation succeded, <0 if something went wrong
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*/
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static int _get_more_prng_bytes(struct prng_context *ctx)
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{
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int i;
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unsigned char tmp[DEFAULT_BLK_SZ];
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unsigned char *output = NULL;
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dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n",
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ctx);
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hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ);
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hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ);
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hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ);
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/*
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* This algorithm is a 3 stage state machine
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*/
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for (i = 0; i < 3; i++) {
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switch (i) {
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case 0:
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/*
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* Start by encrypting the counter value
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* This gives us an intermediate value I
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*/
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memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ);
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output = ctx->I;
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hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ);
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break;
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case 1:
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/*
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* Next xor I with our secret vector V
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* encrypt that result to obtain our
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* pseudo random data which we output
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*/
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xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ);
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hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ);
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output = ctx->rand_data;
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break;
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case 2:
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/*
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* First check that we didn't produce the same
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* random data that we did last time around through this
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*/
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if (!memcmp(ctx->rand_data, ctx->last_rand_data,
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DEFAULT_BLK_SZ)) {
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printk(KERN_ERR
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"ctx %p Failed repetition check!\n",
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ctx);
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ctx->flags |= PRNG_NEED_RESET;
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return -EINVAL;
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}
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memcpy(ctx->last_rand_data, ctx->rand_data,
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DEFAULT_BLK_SZ);
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/*
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* Lastly xor the random data with I
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* and encrypt that to obtain a new secret vector V
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*/
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xor_vectors(ctx->rand_data, ctx->I, tmp,
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DEFAULT_BLK_SZ);
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output = ctx->V;
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hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ);
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break;
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}
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/* do the encryption */
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crypto_cipher_encrypt_one(ctx->tfm, output, tmp);
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}
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/*
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* Now update our DT value
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*/
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for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) {
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ctx->DT[i] += 1;
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if (ctx->DT[i] != 0)
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break;
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}
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dbgprint("Returning new block for context %p\n", ctx);
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ctx->rand_data_valid = 0;
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hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ);
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hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ);
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hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ);
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hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ);
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return 0;
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}
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/* Our exported functions */
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static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx)
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{
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unsigned long flags;
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unsigned char *ptr = buf;
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unsigned int byte_count = (unsigned int)nbytes;
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int err;
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if (nbytes < 0)
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return -EINVAL;
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spin_lock_irqsave(&ctx->prng_lock, flags);
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err = -EINVAL;
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if (ctx->flags & PRNG_NEED_RESET)
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goto done;
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/*
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* If the FIXED_SIZE flag is on, only return whole blocks of
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* pseudo random data
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*/
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err = -EINVAL;
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if (ctx->flags & PRNG_FIXED_SIZE) {
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if (nbytes < DEFAULT_BLK_SZ)
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goto done;
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byte_count = DEFAULT_BLK_SZ;
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}
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err = byte_count;
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dbgprint(KERN_CRIT "getting %d random bytes for context %p\n",
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byte_count, ctx);
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remainder:
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if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
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if (_get_more_prng_bytes(ctx) < 0) {
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memset(buf, 0, nbytes);
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err = -EINVAL;
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goto done;
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}
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}
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/*
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* Copy any data less than an entire block
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*/
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if (byte_count < DEFAULT_BLK_SZ) {
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empty_rbuf:
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for (; ctx->rand_data_valid < DEFAULT_BLK_SZ;
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ctx->rand_data_valid++) {
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*ptr = ctx->rand_data[ctx->rand_data_valid];
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ptr++;
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byte_count--;
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if (byte_count == 0)
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goto done;
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}
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}
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/*
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* Now copy whole blocks
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*/
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for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) {
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if (ctx->rand_data_valid == DEFAULT_BLK_SZ) {
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if (_get_more_prng_bytes(ctx) < 0) {
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memset(buf, 0, nbytes);
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err = -EINVAL;
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goto done;
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}
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}
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if (ctx->rand_data_valid > 0)
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goto empty_rbuf;
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memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ);
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ctx->rand_data_valid += DEFAULT_BLK_SZ;
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ptr += DEFAULT_BLK_SZ;
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}
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/*
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* Now go back and get any remaining partial block
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*/
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if (byte_count)
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goto remainder;
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done:
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spin_unlock_irqrestore(&ctx->prng_lock, flags);
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dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n",
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err, ctx);
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return err;
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}
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static void free_prng_context(struct prng_context *ctx)
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{
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crypto_free_cipher(ctx->tfm);
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}
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static int reset_prng_context(struct prng_context *ctx,
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unsigned char *key, size_t klen,
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unsigned char *V, unsigned char *DT)
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{
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int ret;
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int rc = -EINVAL;
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unsigned char *prng_key;
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spin_lock(&ctx->prng_lock);
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ctx->flags |= PRNG_NEED_RESET;
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prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY;
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if (!key)
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klen = DEFAULT_PRNG_KSZ;
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if (V)
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memcpy(ctx->V, V, DEFAULT_BLK_SZ);
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else
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memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ);
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if (DT)
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memcpy(ctx->DT, DT, DEFAULT_BLK_SZ);
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else
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memset(ctx->DT, 0, DEFAULT_BLK_SZ);
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memset(ctx->rand_data, 0, DEFAULT_BLK_SZ);
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memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ);
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if (ctx->tfm)
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crypto_free_cipher(ctx->tfm);
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ctx->tfm = crypto_alloc_cipher("aes", 0, 0);
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if (IS_ERR(ctx->tfm)) {
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dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n",
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ctx);
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ctx->tfm = NULL;
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goto out;
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}
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ctx->rand_data_valid = DEFAULT_BLK_SZ;
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ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen);
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if (ret) {
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dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n",
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crypto_cipher_get_flags(ctx->tfm));
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crypto_free_cipher(ctx->tfm);
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goto out;
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}
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rc = 0;
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ctx->flags &= ~PRNG_NEED_RESET;
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out:
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spin_unlock(&ctx->prng_lock);
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return rc;
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}
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static int cprng_init(struct crypto_tfm *tfm)
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{
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struct prng_context *ctx = crypto_tfm_ctx(tfm);
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spin_lock_init(&ctx->prng_lock);
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if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0)
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return -EINVAL;
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/*
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* after allocation, we should always force the user to reset
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* so they don't inadvertently use the insecure default values
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* without specifying them intentially
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*/
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ctx->flags |= PRNG_NEED_RESET;
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return 0;
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}
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static void cprng_exit(struct crypto_tfm *tfm)
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{
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free_prng_context(crypto_tfm_ctx(tfm));
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}
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static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata,
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unsigned int dlen)
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{
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struct prng_context *prng = crypto_rng_ctx(tfm);
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return get_prng_bytes(rdata, dlen, prng);
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}
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/*
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* This is the cprng_registered reset method the seed value is
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* interpreted as the tuple { V KEY DT}
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* V and KEY are required during reset, and DT is optional, detected
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* as being present by testing the length of the seed
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*/
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static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen)
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{
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struct prng_context *prng = crypto_rng_ctx(tfm);
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u8 *key = seed + DEFAULT_BLK_SZ;
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u8 *dt = NULL;
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if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
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return -EINVAL;
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if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ))
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dt = key + DEFAULT_PRNG_KSZ;
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reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt);
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if (prng->flags & PRNG_NEED_RESET)
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return -EINVAL;
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return 0;
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}
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static struct crypto_alg rng_alg = {
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.cra_name = "stdrng",
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.cra_driver_name = "ansi_cprng",
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.cra_priority = 100,
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.cra_flags = CRYPTO_ALG_TYPE_RNG,
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.cra_ctxsize = sizeof(struct prng_context),
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.cra_type = &crypto_rng_type,
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.cra_module = THIS_MODULE,
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.cra_list = LIST_HEAD_INIT(rng_alg.cra_list),
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.cra_init = cprng_init,
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.cra_exit = cprng_exit,
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.cra_u = {
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.rng = {
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.rng_make_random = cprng_get_random,
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.rng_reset = cprng_reset,
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.seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ,
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}
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}
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};
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/* Module initalization */
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static int __init prng_mod_init(void)
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{
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int ret = 0;
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if (fips_enabled)
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rng_alg.cra_priority += 200;
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ret = crypto_register_alg(&rng_alg);
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if (ret)
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goto out;
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out:
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return 0;
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}
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static void __exit prng_mod_fini(void)
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{
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crypto_unregister_alg(&rng_alg);
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return;
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}
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MODULE_LICENSE("GPL");
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MODULE_DESCRIPTION("Software Pseudo Random Number Generator");
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MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>");
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module_param(dbg, int, 0);
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MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)");
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module_init(prng_mod_init);
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module_exit(prng_mod_fini);
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MODULE_ALIAS("stdrng");
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