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

[Andreas Rheinhardt]

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