[FFmpeg-devel] [PATCH 1/2] avcodec: add mvdv video decoder

[Paul B Mahol]

On 11/26/19, James Almer <jamrial at gmail.com> wrote:
> On 11/26/2019 4:29 PM, Paul B Mahol wrote:
>> On 11/26/19, James Almer <jamrial at gmail.com> wrote:
>>> On 11/26/2019 6:47 AM, Paul B Mahol wrote:
>>>> On 11/25/19, Tomas Härdin <tjoppen at acc.umu.se> wrote:
>>>>> mån 2019-11-25 klockan 22:09 +0100 skrev Paul B Mahol:
>>>>>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>>>>>> +static int decode_mvdv(MidiVidContext *s, AVCodecContext *avctx,
>>>>>> AVFrame
>>>>>> *frame)
>>>>>> +{
>>>>>> +    GetByteContext *gb = &s->gb;
>>>>>> +    GetBitContext mask;
>>>>>> +    GetByteContext idx9;
>>>>>> +    uint16_t nb_vectors, intra_flag;
>>>>>> +    const uint8_t *vec;
>>>>>> +    const uint8_t *mask_start;
>>>>>> +    uint8_t *skip;
>>>>>> +    int mask_size;
>>>>>> +    int idx9bits = 0;
>>>>>> +    int idx9val = 0;
>>>>>> +    int num_blocks;
>>>>>> +
>>>>>> +    nb_vectors = bytestream2_get_le16(gb);
>>>>>> +    intra_flag = bytestream2_get_le16(gb);
>>>>>> +    if (intra_flag) {
>>>>>> +        num_blocks = (avctx->width / 2) * (avctx->height / 2);
>>>>>
>>>>> Will UB if width*height/4 > INT_MAX
>>>>>
>>>>>> +    } else {
>>>>>> +        int skip_linesize;
>>>>>> +
>>>>>> +        num_blocks = bytestream2_get_le32(gb);
>>>>>
>>>>> Might want to use uint32_t so this doesn't lead to weirdness on 32-bit
>>>>>
>>>>>> +        skip_linesize = avctx->width >> 1;
>>>>>> +        mask_start = gb->buffer_start + bytestream2_tell(gb);
>>>>>> +        mask_size = (avctx->width >> 5) * (avctx->height >> 2);
>>>>>
>>>>> This can also UB
>>>>>
>>>>> /Tomas
>>>>>
>>>>> _______________________________________________
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>>>>
>>>> Nothing of this can actually happen.
>>>
>>> It can and i'm fairly sure it will happen as soon as the fuzzer starts
>>> testing this decoder using big dimensions.
>>
>> I'm not that guy doing such work. Please stop bikesheding those
>> patches for once.
>>
>>>
>>> You don't need asserts here, you just need to check the calculations
>>> will not overflow. Do something like "if ((int64_t)avctx->width *
>>> avctx->height / 4 > INT_MAX) return AVERROR_INVALIDDATA" and call it a
>>> day.
>>> Also, maybe num_blocks should be unsigned, seeing you set it using
>>> bytestream2_get_le32() for P-frames.
>>
>> No decoder does this.
>
> Most decoders call av_image_check_size2() directly or indirectly to set
> dimensions, which does w*h overflow checks similar to the one above.
>

Only if they store width/height out of container.