> On Jun 10, 2025, at 11:13 AM, Ross Philipson <[email protected]>
> wrote:
>
> On 6/10/25 10:47 AM, Lidong Chen wrote:
>> In LzmaEnc_CodeOneBlock(), both GetOptimumFast() and GetOptimum()
>> returns a value of greater or equal to 1, which is assigned to
>> 'len'. But since LZMA_MATCH_LEN_MIN == 2, 'len' should be validated
>> before performing "len - LZMA_MATCH_LEN_MIN" to avoid underflow
>> when 'len' equals to 1.
>
> It seems odd that these internal calls will produce values for len that the
> calling code can't use and it ends in an error. Does this happen when the
> input data is bad/malformed/etc? Is it considered an error condition down in
> those functions when they result in len being set to 1 or 2?
It looks to me that the call to GetOptimum() or GetOptimumFast() returns an
encoding
decision, not the condition of the input data (line 1840 & 1871).
if (p->fastMode)
len = GetOptimumFast(p, &pos);
else
len = GetOptimum(p, nowPos32, &pos);
if (len == 1 && pos == 0xFFFFFFFF)
{
1840 p->state = kLiteralNextStates[p->state];
}
else
{
if (pos < LZMA_NUM_REPS)
{
if (len == 1)
1871 p->state = kShortRepNextStates[p->state];
}
else
{
LenEnc_Encode2(&p->lenEnc, &p->rc, len - LZMA_MATCH_LEN_MIN, posState,
!p->fastMode, p->ProbPrices);
}
}
Thanks,
Lidong
>
> Thanks
> Ross
>
>> Fixed: CID 51508
>> Signed-off-by: Lidong Chen <[email protected]>
>> ---
>> grub-core/lib/LzmaEnc.c | 5 +++++
>> 1 file changed, 5 insertions(+)
>> diff --git a/grub-core/lib/LzmaEnc.c b/grub-core/lib/LzmaEnc.c
>> index 52b331558..d74e96303 100644
>> --- a/grub-core/lib/LzmaEnc.c
>> +++ b/grub-core/lib/LzmaEnc.c
>> @@ -1880,6 +1880,11 @@ static SRes LzmaEnc_CodeOneBlock(CLzmaEnc *p, Bool
>> useLimits, UInt32 maxPackSize
>> UInt32 posSlot, lenToPosState;
>> RangeEnc_EncodeBit(&p->rc, &p->isRep[p->state], 0);
>> p->state = kMatchNextStates[p->state];
>> + if (len < LZMA_MATCH_LEN_MIN)
>> + {
>> + p->result = SZ_ERROR_DATA;
>> + return CheckErrors(p);
>> + }
>> LenEnc_Encode2(&p->lenEnc, &p->rc, len - LZMA_MATCH_LEN_MIN,
>> posState, !p->fastMode, p->ProbPrices);
>> pos -= LZMA_NUM_REPS;
>> GetPosSlot(pos, posSlot);
>
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