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

[Paul B Mahol]

On 5/12/17, Michael Niedermayer <michael at niedermayer.cc> wrote:
> On Thu, May 11, 2017 at 11:17:33AM +0200, Michael Niedermayer wrote:
>> 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
>
> ping, this is a security issue and needs to be fixed


I told you that its unacceptable.

Do this: avpkt->data[avpkt->size] = 0;