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

[Michael Niedermayer]

On Thu, May 11, 2017 at 09:01:57AM +0200, Paul B Mahol wrote:
> 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
> >
> > _______________________________________________
> > ffmpeg-devel mailing list
> > ffmpeg-devel at ffmpeg.org
> > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> >
> 
> This is suboptimal solution.

That comment isnt helpfull in improving the patch. It doesnt say
what it is that you would like changed.

I could probably replace string functions and avoid copying the whole
packet if thats what you suggest ?
it makes this bugfix more complex though

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Frequently ignored answer#1 FFmpeg bugs should be sent to our bugtracker. User
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And questions about how to use libav* should be sent to the libav-user ML.
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