[PATCH] erofs-utils: lib: reset hc to avoid 32-bit overflow of kite-deflate

[Yifan Zhao]

On 2024/1/24 17:53, Gao Xiang wrote:
> Hi Yifan,
>
> On 2024/1/24 17:47, Yifan Zhao wrote:
>>
>> On 1/24/24 17:16, Gao Xiang wrote:
>>> Yifan reported a "segmentation fault (core dumped)" error days ago
>>> with a large dataset (enwik9 x 5).   Let's fix it.
>>>
>>> Reported-by: Yifan Zhao <zhaoyifan at sjtu.edu.cn>
>>> Fixes: 861037f4fc15 ("erofs-utils: add a built-in DEFLATE compressor")
>>> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
>>> ---
>>>   include/erofs/defs.h |  3 +++
>>>   lib/kite_deflate.c   | 12 ++++++++++++
>>>   2 files changed, 15 insertions(+)
>>>
>>> diff --git a/include/erofs/defs.h b/include/erofs/defs.h
>>> index e7384a1..4ea9a55 100644
>>> --- a/include/erofs/defs.h
>>> +++ b/include/erofs/defs.h
>>> @@ -343,6 +343,9 @@ unsigned long __roundup_pow_of_two(unsigned long n)
>>>   #define ST_MTIM_NSEC(stbuf) 0
>>>   #endif
>>> +#define likely(x)      __builtin_expect(!!(x), 1)
>>> +#define unlikely(x)    __builtin_expect(!!(x), 0)
>>> +
>>>   #ifdef __cplusplus
>>>   }
>>>   #endif
>>> diff --git a/lib/kite_deflate.c b/lib/kite_deflate.c
>>> index 8667954..cb81626 100644
>>> --- a/lib/kite_deflate.c
>>> +++ b/lib/kite_deflate.c
>>> @@ -859,6 +859,18 @@ static void kite_mf_reset(struct 
>>> kite_matchfinder *mf,
>>>        */
>>>       mf->base += mf->offset + kHistorySize32 + 1;
>>> +    /*
>>> +     * Unlike other LZ encoders like liblzma [1], we simply reset 
>>> the hash
>>> +     * chain instead of normalization.  This avoids extra 
>>> complexity, as we
>>> +     * don't consider extreme large input buffers in one go.
>>> +     *
>>> +     * [1] 
>>> https://github.com/tukaani-project/xz/blob/v5.4.0/src/liblzma/lz/lz_encoder_mf.c#L94
>>> +     */
>>> +    if (unlikely(mf->base > ((typeof(mf->base))-1) >> 1)) {
>>> +        mf->base = kHistorySize32 + 1;
>>> +        memset(mf->hash, 0, 0x10000 * sizeof(mf->hash[0]));
>>> +        memset(mf->chain, 0, sizeof(mf->chain[0]) * mf->wsiz);
>
> This line
>
> memset(mf->chain, 0, sizeof(mf->chain[0]) * mf->wsiz);
>
> is also unnecessary, let me remove it when applying.
>
> I think it still works on your side.
>
>
>>> +    }
>>>       mf->offset = 0;
>>>       mf->cyclic_pos = 0;
>>
>> Tested-by: Yifan Zhao <zhaoyifan at sjtu.edu.cn>
>
> Thanks!
>
> Thanks,
> Gao Xiang
>
>>
>>
>> Yifan Zhao
>>
>> Thanks


Yes, it still works for me.

Tested-by: Yifan Zhao <zhaoyifan at sjtu.edu.cn>


Thanks,

Yifan Zhao