[PATCH] avcodec/ac3dec: Check expacc
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/ac3dec.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c index a95c204..499971a 100644 --- a/libavcodec/ac3dec.c +++ b/libavcodec/ac3dec.c @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s, group_size = exp_strategy + (exp_strategy == EXP_D45); for (grp = 0, i = 0; grp < ngrps; grp++) { expacc = get_bits(gbc, 7); + if (expacc >= 125) { + av_log(s->avctx, AV_LOG_ERROR, "expacc %d is out-of-range\n", expacc); + return AVERROR_INVALIDDATA; + } dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2]; -- 2.10.2
On 03.11.2016 11:30, Michael Niedermayer wrote:
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/ac3dec.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c index a95c204..499971a 100644 --- a/libavcodec/ac3dec.c +++ b/libavcodec/ac3dec.c @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s, group_size = exp_strategy + (exp_strategy == EXP_D45); for (grp = 0, i = 0; grp < ngrps; grp++) { expacc = get_bits(gbc, 7); + if (expacc >= 125) {
This is somewhat a magic number, which can be understood from reading section "7.1.2 Exponent Strategy" of the ac3 specification, in short: Three exponents each represented as number 0-4 are grouped together and base-5 encoded, so the maximal correct value is 25*4 + 5*4 + 4 = 124. Maybe mention this in the commit message.
+ av_log(s->avctx, AV_LOG_ERROR, "expacc %d is out-of-range\n", expacc); + return AVERROR_INVALIDDATA; + } dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2];
Anyway, the change itself looks good to me. Best regards, Andreas
On Thu, Nov 03, 2016 at 09:18:57PM +0100, Andreas Cadhalpun wrote:
On 03.11.2016 11:30, Michael Niedermayer wrote:
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/ac3dec.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c index a95c204..499971a 100644 --- a/libavcodec/ac3dec.c +++ b/libavcodec/ac3dec.c @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s, group_size = exp_strategy + (exp_strategy == EXP_D45); for (grp = 0, i = 0; grp < ngrps; grp++) { expacc = get_bits(gbc, 7); + if (expacc >= 125) {
This is somewhat a magic number, which can be understood from reading section "7.1.2 Exponent Strategy" of the ac3 specification, in short: Three exponents each represented as number 0-4 are grouped together and base-5 encoded, so the maximal correct value is 25*4 + 5*4 + 4 = 124.
Maybe mention this in the commit message.
added, applied thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Dictatorship naturally arises out of democracy, and the most aggravated form of tyranny and slavery out of the most extreme liberty. -- Plato
On 11/3/16, Michael Niedermayer <michael@niedermayer.cc> wrote:
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/ac3dec.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c index a95c204..499971a 100644 --- a/libavcodec/ac3dec.c +++ b/libavcodec/ac3dec.c @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s, group_size = exp_strategy + (exp_strategy == EXP_D45); for (grp = 0, i = 0; grp < ngrps; grp++) { expacc = get_bits(gbc, 7); + if (expacc >= 125) { + av_log(s->avctx, AV_LOG_ERROR, "expacc %d is out-of-range\n", expacc); + return AVERROR_INVALIDDATA; + } dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2]; --
Please revert this ASAP. It breaks decoding valid files.
On Thu, Mar 03, 2022 at 06:36:29PM +0100, Paul B Mahol wrote:
On 11/3/16, Michael Niedermayer <michael@niedermayer.cc> wrote:
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavcodec/ac3dec.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c index a95c204..499971a 100644 --- a/libavcodec/ac3dec.c +++ b/libavcodec/ac3dec.c @@ -426,6 +426,10 @@ static int decode_exponents(AC3DecodeContext *s, group_size = exp_strategy + (exp_strategy == EXP_D45); for (grp = 0, i = 0; grp < ngrps; grp++) { expacc = get_bits(gbc, 7); + if (expacc >= 125) { + av_log(s->avctx, AV_LOG_ERROR, "expacc %d is out-of-range\n", expacc); + return AVERROR_INVALIDDATA; + } dexp[i++] = ungroup_3_in_7_bits_tab[expacc][0]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][1]; dexp[i++] = ungroup_3_in_7_bits_tab[expacc][2]; --
Please revert this ASAP. It breaks decoding valid files.
please provide an affected file / link to one thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB "You are 36 times more likely to die in a bathtub than at the hands of a terrorist. Also, you are 2.5 times more likely to become a president and 2 times more likely to become an astronaut, than to die in a terrorist attack." -- Thoughty2
participants (3)
-
Andreas Cadhalpun -
Michael Niedermayer -
Paul B Mahol