[FFmpeg-devel] [PATCH] avcodec/xpmdec: Fix multiple pointer/memory issues

[Paul B Mahol]

On 5/11/17, Michael Niedermayer <michael at niedermayer.cc> wrote:
> Most of these were found through code review in response to
> fixing 1466/clusterfuzz-testcase-minimized-5961584419536896
> There is thus no testcase for most of this.
> The initial issue was Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/xpmdec.c | 37 ++++++++++++++++++++++++++++++-------
>  1 file changed, 30 insertions(+), 7 deletions(-)
>
> diff --git a/libavcodec/xpmdec.c b/libavcodec/xpmdec.c
> index 9112d4cb5e..03172e4aad 100644
> --- a/libavcodec/xpmdec.c
> +++ b/libavcodec/xpmdec.c
> @@ -29,6 +29,8 @@
>  typedef struct XPMContext {
>      uint32_t  *pixels;
>      int        pixels_size;
> +    uint8_t   *buf;
> +    int        buf_size;
>  } XPMDecContext;
>
>  typedef struct ColorEntry {
> @@ -233,6 +235,8 @@ static uint32_t color_string_to_rgba(const char *p, int
> len)
>      const ColorEntry *entry;
>      char color_name[100];
>
> +    len = FFMIN(FFMAX(len, 0), sizeof(color_name) - 1);
> +
>      if (*p == '#') {
>          p++;
>          len--;
> @@ -299,18 +303,25 @@ static int xpm_decode_frame(AVCodecContext *avctx,
> void *data,
>  {
>      XPMDecContext *x = avctx->priv_data;
>      AVFrame *p=data;
> -    const uint8_t *end, *ptr = avpkt->data;
> +    const uint8_t *end, *ptr;
>      int ncolors, cpp, ret, i, j;
>      int64_t size;
>      uint32_t *dst;
>
>      avctx->pix_fmt = AV_PIX_FMT_BGRA;
>
> -    end = avpkt->data + avpkt->size;
> -    while (memcmp(ptr, "/* XPM */", 9) && ptr < end - 9)
> +    av_fast_padded_malloc(&x->buf, &x->buf_size, avpkt->size);
> +    if (!x->buf)
> +        return AVERROR(ENOMEM);
> +    memcpy(x->buf, avpkt->data, avpkt->size);
> +    x->buf[avpkt->size] = 0;
> +
> +    ptr = x->buf;
> +    end = x->buf + avpkt->size;
> +    while (end - ptr > 9 && memcmp(ptr, "/* XPM */", 9))
>          ptr++;
>
> -    if (ptr >= end) {
> +    if (end - ptr <= 9) {
>          av_log(avctx, AV_LOG_ERROR, "missing signature\n");
>          return AVERROR_INVALIDDATA;
>      }
> @@ -335,7 +346,7 @@ static int xpm_decode_frame(AVCodecContext *avctx, void
> *data,
>
>      size = 1;
>      for (i = 0; i < cpp; i++)
> -        size *= 94;
> +        size *= 95;
>
>      if (ncolors <= 0 || ncolors > size) {
>          av_log(avctx, AV_LOG_ERROR, "invalid number of colors: %d\n",
> ncolors);
> @@ -349,12 +360,15 @@ static int xpm_decode_frame(AVCodecContext *avctx,
> void *data,
>          return AVERROR(ENOMEM);
>
>      ptr += mod_strcspn(ptr, ",") + 1;
> +    if (end - ptr < 1)
> +        return AVERROR_INVALIDDATA;
> +
>      for (i = 0; i < ncolors; i++) {
>          const uint8_t *index;
>          int len;
>
>          ptr += mod_strcspn(ptr, "\"") + 1;
> -        if (ptr + cpp > end)
> +        if (end - ptr < cpp)
>              return AVERROR_INVALIDDATA;
>          index = ptr;
>          ptr += cpp;
> @@ -373,14 +387,20 @@ static int xpm_decode_frame(AVCodecContext *avctx,
> void *data,
>
>          x->pixels[ret] = color_string_to_rgba(ptr, len);
>          ptr += mod_strcspn(ptr, ",") + 1;
> +        if (end - ptr < 1)
> +            return AVERROR_INVALIDDATA;
>      }
>
>      for (i = 0; i < avctx->height; i++) {
>          dst = (uint32_t *)(p->data[0] + i * p->linesize[0]);
> +        if (end - ptr < 1)
> +            return AVERROR_INVALIDDATA;
>          ptr += mod_strcspn(ptr, "\"") + 1;
> +        if (end - ptr < 1)
> +            return AVERROR_INVALIDDATA;
>
>          for (j = 0; j < avctx->width; j++) {
> -            if (ptr + cpp > end)
> +            if (end - ptr < cpp)
>                  return AVERROR_INVALIDDATA;
>
>              if ((ret = ascii2index(ptr, cpp)) < 0)
> @@ -405,6 +425,9 @@ static av_cold int xpm_decode_close(AVCodecContext
> *avctx)
>      XPMDecContext *x = avctx->priv_data;
>      av_freep(&x->pixels);
>
> +    av_freep(&x->buf);
> +    x->buf_size = 0;
> +
>      return 0;
>  }
>
> --
> 2.11.0
>
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>

This is suboptimal solution.