diff options
Diffstat (limited to 'src/crypto/tree-hash.c')
| -rw-r--r-- | src/crypto/tree-hash.c | 54 |
1 files changed, 48 insertions, 6 deletions
diff --git a/src/crypto/tree-hash.c b/src/crypto/tree-hash.c index a1c21d72b..573f44643 100644 --- a/src/crypto/tree-hash.c +++ b/src/crypto/tree-hash.c @@ -35,7 +35,43 @@ #include "hash-ops.h" +/// Quick check if this is power of two (use on unsigned types; in this case for size_t only) +bool ispowerof2_size_t(size_t x) { + return x && !(x & (x - 1)); +} + +/*** +* Round to power of two, for count>=3 and for count being not too large (as reasonable for tree hash calculations) +*/ +size_t tree_hash_cnt(size_t count) { + assert( count >= 3); // cases for 0,1,2 are handled elsewhere + // Round down the count size: fun(2**n)= 2**(n-1) to round down to power of two + size_t tmp = count - 1; + size_t jj = 1; + for (jj=1 ; tmp != 0 ; ++jj) { + tmp /= 2; // dividing by 2 until to get how many powers of 2 fits size_to tmp + } + size_t cnt = 1 << (jj-2); // cnt is the count, but rounded down to power of two + // printf("count=%zu cnt=%zu jj=%zu tmp=%zu \n" , count,cnt,jj,tmp); + assert( cnt > 0 ); assert( cnt >= count/2 ); assert( cnt <= count ); + assert( ispowerof2_size_t( cnt )); + return cnt; +} + void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) { +// The blockchain block at height 202612 http://monerochain.info/block/bbd604d2ba11ba27935e006ed39c9bfdd99b76bf4a50654bc1e1e61217962698 +// contained 514 transactions, that triggered bad calculation of variable "cnt" in the original version of this function +// as from CryptoNote code. +// +// This bug applies to all CN altcoins. +// +// Mathematical bug here was first published on 14:45:34 (GMT+2) 2014-09-04 by Rafal Freeman <rfree> +// https://github.com/rfree2monero/bitmonero/commit/b417abfb7a297d09f1bbb6de29030f8de9952ac8 +// and soon also applied to CryptoNote (15:10 GMT+2), and BoolBerry used not fully correct work around: +// the work around of sizeof(size_t)*8 or <<3 as used before in 2 coins and in BBL later was blocking +// exploitation on normal platforms, how ever we strongly recommend the following fix because it removes +// mistake in mathematical formula. + assert(count > 0); if (count == 1) { memcpy(root_hash, hashes, HASH_SIZE); @@ -43,24 +79,30 @@ void tree_hash(const char (*hashes)[HASH_SIZE], size_t count, char *root_hash) { cn_fast_hash(hashes, 2 * HASH_SIZE, root_hash); } else { size_t i, j; - size_t cnt = count - 1; + + size_t cnt = tree_hash_cnt( count ); + size_t max_size_t = (size_t) -1; // max allowed value of size_t + assert( cnt < max_size_t/2 ); // reasonable size to avoid any overflows. /2 is extra; Anyway should be limited much stronger by logical code + // as we have sane limits on transactions counts in blockchain rules + char (*ints)[HASH_SIZE]; - for (i = 1; i < sizeof(size_t); i <<= 1) { - cnt |= cnt >> i; - } - cnt &= ~(cnt >> 1); - ints = alloca(cnt * HASH_SIZE); + size_t ints_size = cnt * HASH_SIZE; + ints = alloca(ints_size); memset( ints , 0 , ints_size); // allocate, and zero out as extra protection for using uninitialized mem + memcpy(ints, hashes, (2 * cnt - count) * HASH_SIZE); + for (i = 2 * cnt - count, j = 2 * cnt - count; j < cnt; i += 2, ++j) { cn_fast_hash(hashes[i], 64, ints[j]); } assert(i == count); + while (cnt > 2) { cnt >>= 1; for (i = 0, j = 0; j < cnt; i += 2, ++j) { cn_fast_hash(ints[i], 64, ints[j]); } } + cn_fast_hash(ints[0], 64, root_hash); } } |