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Stop out-of-bounds read, and ensure all bytes are used, in FuncIntRandomMT #2716

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merged 2 commits into from
Aug 22, 2018
Merged

Stop out-of-bounds read, and ensure all bytes are used, in FuncIntRandomMT #2716

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a1f8928
Stop out-of-bounds read in FuncIntRandomMT
ChrisJefferson Jul 4, 2018
044db55
Use all bytes of string for initialising MersenneTwister
ChrisJefferson Aug 21, 2018
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33 changes: 23 additions & 10 deletions src/intfuncs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,22 +62,34 @@ void initGRMT(UInt4 *mt, UInt4 s)
mt[624] = mti;
}

// Read s[pos], returning 0 if pos is past the error of the array
static inline UChar checkedReadChar(UChar * s, UInt4 pos, UInt4 len)
{
if (pos < len)
return s[pos];
else
return 0;
}

/* to read a seed string independently of endianness */
static inline UInt4 uint4frombytes(UChar *s)
static inline UInt4 uint4frombytes(UChar * s, UInt4 pos, UInt4 len)
{
UInt4 res;
res = s[3]; res <<= 8;
res += s[2]; res <<= 8;
res += s[1]; res <<= 8;
res += s[0];
res = checkedReadChar(s, pos + 3, len);
res <<= 8;
res += checkedReadChar(s, pos + 2, len);
res <<= 8;
res += checkedReadChar(s, pos + 1, len);
res <<= 8;
res += checkedReadChar(s, pos + 0, len);
return res;
}

Obj FuncInitRandomMT( Obj self, Obj initstr)
{
Obj str;
UChar *init_key;
UInt4 *mt, key_length, i, j, k, N=624;
UInt4 *mt, key_length, byte_key_length, i, j, k, N = 624;

/* check the seed, given as string */
while (! IsStringConv(initstr)) {
Expand All @@ -97,15 +109,16 @@ Obj FuncInitRandomMT( Obj self, Obj initstr)
i=1; j=0;
/* Do not set these up until all garbage collection is done */
init_key = CHARS_STRING(initstr);
key_length = GET_LEN_STRING(initstr) / 4;
byte_key_length = GET_LEN_STRING(initstr);
key_length = byte_key_length / 4;
k = (N>key_length ? N : key_length);
for (; k; k--) {
mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >> 30)) * 1664525UL))
+ uint4frombytes(init_key+4*j) + j;
mt[i] = (mt[i] ^ ((mt[i - 1] ^ (mt[i - 1] >> 30)) * 1664525UL)) +
uint4frombytes(init_key, 4 * j, byte_key_length) + j;
mt[i] &= 0xffffffffUL;
i++; j++;
if (i>=N) { mt[0] = mt[N-1]; i=1; }
if (j>=key_length) j=0;
if (4 * j >= byte_key_length) j=0;
}
for (k=N-1; k; k--) {
mt[i] = (mt[i] ^ ((mt[i-1] ^ (mt[i-1] >> 30)) * 1566083941UL)) - i;
Expand Down
25 changes: 25 additions & 0 deletions tst/testinstall/random.tst
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Original file line number Diff line number Diff line change
Expand Up @@ -154,5 +154,30 @@ gap> randomTest([1,-6,"cheese", Group(())], Random);
gap> randomTest(PadicExtensionNumberFamily(3, 5, [1,1,1], [1,1]), Random, function(x,y) return IsPadicExtensionNumber(x); end);
gap> randomTest(PurePadicNumberFamily(2,20), Random, function(x,y) return IsPurePadicNumber(x); end);

# Test initialising random number generator
# We take a string and 0-pad it to 4 bytes
gap> getOneInt := function(str)
> Init(GlobalMersenneTwister, str);
> return Random([1..100000]);
> end;;
gap> getOneInt("") = getOneInt("\000");
true
gap> getOneInt("a") = getOneInt("b");
false
gap> getOneInt("") = getOneInt("\000\000\000\000");
true
gap> getOneInt("a") = getOneInt("a\000");
true
gap> getOneInt("a") = getOneInt("a\000\000\000");
true
gap> getOneInt("a") = getOneInt("a\000\000\000\000");
false
gap> getOneInt("a") = getOneInt("a\000\000\000a\000\000\000");
false
gap> getOneInt("a\000\000\000a\000\000\000") = getOneInt("a\000\000\000a");
true
gap> getOneInt("a") = getOneInt("a\000\000\000b");
false

#
gap> STOP_TEST("random.tst", 1);