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webp: ensure that each transform is only used once

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According to the WebP Lossless Bitstream Specification
"each transform is allowed to be used only once".

If a transform is more than once this can lead to memory
corruption.

Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>
This commit is contained in:
Andreas Cadhalpun 2015-03-05 22:48:28 +01:00 committed by Anton Khirnov
parent cf18e777ae
commit 30e6abd1a8
1 changed files with 9 additions and 1 deletions
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10
libavcodec/webp.c
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@ -1081,7 +1081,7 @@ static int vp8_lossless_decode_frame(AVCodecContext *avctx, AVFrame *p,
unsigned int data_size, int is_alpha_chunk)
{
WebPContext *s = avctx->priv_data;
int w, h, ret, i;
int w, h, ret, i, used;
if (!is_alpha_chunk) {
s->lossless = 1;
@ -1131,9 +1131,17 @@ static int vp8_lossless_decode_frame(AVCodecContext *avctx, AVFrame *p,
/* parse transformations */
s->nb_transforms = 0;
s->reduced_width = 0;
used = 0;
while (get_bits1(&s->gb)) {
enum TransformType transform = get_bits(&s->gb, 2);
s->transforms[s->nb_transforms++] = transform;
if (used & (1 << transform)) {
av_log(avctx, AV_LOG_ERROR, "Transform %d used more than once\n",
transform);
ret = AVERROR_INVALIDDATA;
goto free_and_return;
}
used |= (1 << transform);
switch (transform) {
case PREDICTOR_TRANSFORM:
ret = parse_transform_predictor(s);