[FFmpeg-devel] [PATCH v2] avformat/jpegxl_anim_dec: avoid overrun with jxlp boxes in container

[Leo Izen]

On 6/16/23 15:00, Andreas Rheinhardt wrote:
> Leo Izen:
>> This switches the jpegxl_collect_codestream_header function to use
>> avcodec/bytestream2, which better enforces barriers, and should avoid
>> overrunning buffers with jxlp boxes if the size is zero or if the size
>> is so small the box is invalid.
>>
>> Signed-off-by: Leo Izen <leo.izen at gmail.com>
>> ---
>>   libavformat/jpegxl_anim_dec.c | 56 +++++++++++++++++++----------------
>>   1 file changed, 30 insertions(+), 26 deletions(-)
>>
>> diff --git a/libavformat/jpegxl_anim_dec.c b/libavformat/jpegxl_anim_dec.c
>> index 6ea6c46d8f..ec400c955c 100644
>> --- a/libavformat/jpegxl_anim_dec.c
>> +++ b/libavformat/jpegxl_anim_dec.c
>> @@ -28,6 +28,7 @@
>>   #include <stdint.h>
>>   #include <string.h>
>>   
>> +#include "libavcodec/bytestream.h"
>>   #define BITSTREAM_READER_LE
>>   #include "libavcodec/get_bits.h"
>>   
>> @@ -48,62 +49,65 @@ typedef struct JXLAnimDemuxContext {
>>    * returns the number of bytes consumed from input, may be greater than input_len
>>    * if the input doesn't end on an ISOBMFF-box boundary
>>    */
>> -static int jpegxl_collect_codestream_header(const uint8_t *input_buffer, int input_len, uint8_t *buffer, int buflen, int *copied) {
>> -    const uint8_t *b = input_buffer;
>> +static int jpegxl_collect_codestream_header(const uint8_t *input_buffer, int input_len,
>> +                                            uint8_t *buffer, int buflen, int *copied) {
>> +    GetByteContext gb;
>>       *copied = 0;
>> +    bytestream2_init(&gb, input_buffer, input_len);
>>   
>>       while (1) {
>>           uint64_t size;
>>           uint32_t tag;
>>           int head_size = 8;
>>   
>> -        if (b - input_buffer >= input_len - 16)
>> +        if (bytestream2_get_bytes_left(&gb) < 16)
>>               break;
>>   
>> -        size = AV_RB32(b);
>> -        b += 4;
>> +        size = bytestream2_get_be32(&gb);
>>           if (size == 1) {
>> -            size = AV_RB64(b);
>> -            b += 8;
>> +            size = bytestream2_get_be64(&gb);
>>               head_size = 16;
>>           }
>>           /* invalid ISOBMFF size */
>> -        if (size > 0 && size <= head_size)
>> +        if (size && size <= head_size)
>>               return AVERROR_INVALIDDATA;
>> -        if (size > 0)
>> +        if (size)
>>               size -= head_size;
>>   
>> -        tag = AV_RL32(b);
>> -        b += 4;
>> +        tag = bytestream2_get_le32(&gb);
>>           if (tag == MKTAG('j', 'x', 'l', 'p')) {
>> -            b += 4;
>> -            size -= 4;
>> +            if (bytestream2_get_bytes_left(&gb) < 4)
>> +                break;
>> +            bytestream2_skip(&gb, 4);
>> +            if (size) {
>> +                if (size <= 4)
>> +                    return AVERROR_INVALIDDATA;
>> +                size -= 4;
>> +            }
>>           }
>> +        /*
>> +         * size = 0 means "until EOF". this is legal but uncommon
>> +         * here we just set it to the remaining size of the probe buffer
>> +         */
>> +        if (!size)
>> +            size = bytestream2_get_bytes_left(&gb);
>>   
>>           if (tag == MKTAG('j', 'x', 'l', 'c') || tag == MKTAG('j', 'x', 'l', 'p')) {
>> -            /*
>> -             * size = 0 means "until EOF". this is legal but uncommon
>> -             * here we just set it to the remaining size of the probe buffer
>> -             * which at this point should always be nonnegative
>> -             */
>> -            if (size == 0 || size > input_len - (b - input_buffer))
>> -                size = input_len - (b - input_buffer);
>> -
>>               if (size > buflen - *copied)
>>                   size = buflen - *copied;
>>               /*
>>                * arbitrary chunking of the payload makes this memcpy hard to avoid
>>                * in practice this will only be performed one or two times at most
>>                */
>> -            memcpy(buffer + *copied, b, size);
>> -            *copied += size;
>> +            *copied += bytestream2_get_buffer(&gb, buffer + *copied, size);
>> +        } else {
>> +            bytestream2_skip(&gb, size);
>>           }
>> -        b += size;
>> -        if (b >= input_buffer + input_len || *copied >= buflen)
>> +        if (bytestream2_get_bytes_left(&gb) <= 0 || *copied >= buflen)
>>               break;
>>       }
>>   
>> -    return b - input_buffer;
>> +    return bytestream2_tell(&gb);
>>   }
>>   
>>   static int jpegxl_anim_probe(const AVProbeData *p)
> 
> Is there an actual (potential) overrun or is this just a precaution?
> 
> - Andreas
> 

Yea, michaelni sent a cvslog email about it earlier, mail ID 
<20230608002033.GF870501 at pb2>. This fixes that and switches to 
bytestream2 at Anton's recommendation.

- Leo Izen