[FFmpeg-devel] avcodec: validate codec parameters in avcodec_parameters_to_context

Submitted by Andreas Cadhalpun on Oct. 25, 2016, 11:59 p.m.

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Message ID 4c67b844-070a-fbbc-5f99-4bf7c8e510d7@googlemail.com
State New
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Commit Message

Andreas Cadhalpun Oct. 25, 2016, 11:59 p.m.
On 25.10.2016 14:56, Hendrik Leppkes wrote:
> On Tue, Oct 25, 2016 at 2:39 PM, wm4 <nfxjfg@googlemail.com> wrote:
>> On Tue, 25 Oct 2016 09:47:29 +0200
>> Hendrik Leppkes <h.leppkes@gmail.com> wrote:
>>
>>> On Tue, Oct 25, 2016 at 1:50 AM, Andreas Cadhalpun
>>> <andreas.cadhalpun@googlemail.com> wrote:
>>>> This should reduce the impact of a demuxer (or API user) setting bogus
>>>> codec parameters.
>>>>
>>>>
>>>
>>> This seems rather noisy

I've added a macro to make it less noisy.

>>> and doesn't really solve anything, does it?

As you analyze below, it was fixing only a part of the problem.

>>> Decoders still need to validate values instead of blindly trusting
>>> them, and this just hides some problems in these decoders,

Yes, the problem hiding is bad, which is why I added av_assert2's
so that developers can easily check if the validation fails.

>>> instead of
>>> fixing them there. API users of avcodec would not fill
>>> AVCodecParameters, they would fill a codec context directly.
>>
>> You could also argue that the demuxer shouldn't return invalid
>> parameters either.
> 
> It should not, but this patch does not address this.

Indeed, the demuxers should be fixed in addition to this patch.

> There is various combinations of component usage that are possible,
> and in fact are used in the real world:
> 
> avformat -> avcodec
> other demuxer -> avcodec
> avformat -> other decoder
> 
> This patch only addresses the first case, and only if you actually use
> this function (which I for example do not, since I have an abstraction
> layer in between, so I never have AVCodecParameters and AVCodecContext
> in the same function).
> So in short, it just doesn't fix much, and you can still get invalid
> output from avformat, and potentially still undefined behavior in
> avcodec if its fed those values through other means.

For the third case, the demuxers have to be fixed. Having the asserts
in the central code makes it much easier to find these problems.

>> How about this: always convert the params to a temporary codecpar, and
>> provide a function to determine the validity of a codecpar. This way
>> the check could be done in multiple places without duplicating the code
>> needed for it.
> 
> That still sounds odd, although slightly better. At the very least it
> should be a dedicated function that checks the values in a key place,
> say you want to check params that are fed to a decoder, then call this
> check in avcodec_open, because thats something everyone has to call to
> use avcodec.

I tried to implement the suggestions of both of you, see attached patch.

Note that the added asserts are triggered by *many* of my fuzzed samples.
I'm happy to write patches for these cases, if we achieve agreement
that the central check alone is insufficient.
Another noteworthy point is that this patch makes it easy to trigger
the av_assert0 in iff_read_packet. I think that assert should be replaced
with an error return.

Best regards,
Andreas

Comments

Michael Niedermayer Oct. 27, 2016, 8:14 p.m.
On Wed, Oct 26, 2016 at 01:59:59AM +0200, Andreas Cadhalpun wrote:
> On 25.10.2016 14:56, Hendrik Leppkes wrote:
> > On Tue, Oct 25, 2016 at 2:39 PM, wm4 <nfxjfg@googlemail.com> wrote:
> >> On Tue, 25 Oct 2016 09:47:29 +0200
> >> Hendrik Leppkes <h.leppkes@gmail.com> wrote:
> >>
> >>> On Tue, Oct 25, 2016 at 1:50 AM, Andreas Cadhalpun
> >>> <andreas.cadhalpun@googlemail.com> wrote:
> >>>> This should reduce the impact of a demuxer (or API user) setting bogus
> >>>> codec parameters.
> >>>>
> >>>>
> >>>
> >>> This seems rather noisy
> 
> I've added a macro to make it less noisy.
> 
> >>> and doesn't really solve anything, does it?
> 
> As you analyze below, it was fixing only a part of the problem.
> 
> >>> Decoders still need to validate values instead of blindly trusting
> >>> them, and this just hides some problems in these decoders,
> 
> Yes, the problem hiding is bad, which is why I added av_assert2's
> so that developers can easily check if the validation fails.
> 
> >>> instead of
> >>> fixing them there. API users of avcodec would not fill
> >>> AVCodecParameters, they would fill a codec context directly.
> >>
> >> You could also argue that the demuxer shouldn't return invalid
> >> parameters either.
> > 
> > It should not, but this patch does not address this.
> 
> Indeed, the demuxers should be fixed in addition to this patch.
> 
> > There is various combinations of component usage that are possible,
> > and in fact are used in the real world:
> > 
> > avformat -> avcodec
> > other demuxer -> avcodec
> > avformat -> other decoder
> > 
> > This patch only addresses the first case, and only if you actually use
> > this function (which I for example do not, since I have an abstraction
> > layer in between, so I never have AVCodecParameters and AVCodecContext
> > in the same function).
> > So in short, it just doesn't fix much, and you can still get invalid
> > output from avformat, and potentially still undefined behavior in
> > avcodec if its fed those values through other means.
> 
> For the third case, the demuxers have to be fixed. Having the asserts
> in the central code makes it much easier to find these problems.
> 
> >> How about this: always convert the params to a temporary codecpar, and
> >> provide a function to determine the validity of a codecpar. This way
> >> the check could be done in multiple places without duplicating the code
> >> needed for it.
> > 
> > That still sounds odd, although slightly better. At the very least it
> > should be a dedicated function that checks the values in a key place,
> > say you want to check params that are fed to a decoder, then call this
> > check in avcodec_open, because thats something everyone has to call to
> > use avcodec.
> 
> I tried to implement the suggestions of both of you, see attached patch.
> 
> Note that the added asserts are triggered by *many* of my fuzzed samples.
> I'm happy to write patches for these cases, if we achieve agreement
> that the central check alone is insufficient.
> Another noteworthy point is that this patch makes it easy to trigger
> the av_assert0 in iff_read_packet. I think that assert should be replaced
> with an error return.
> 
> Best regards,
> Andreas
> 

>  utils.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 80 insertions(+), 2 deletions(-)
> 40a8bafecb6d289a4220a27ac411fbcac3204952  0001-avcodec-validate-codec-parameters.patch
> From f371be7a027da3958e221b4dc88ad558c1489107 Mon Sep 17 00:00:00 2001
> From: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
> Date: Tue, 25 Oct 2016 01:45:27 +0200
> Subject: [PATCH] avcodec: validate codec parameters
> 
> This should reduce the impact of a broken demuxer (or API user) setting bogus
> codec parameters.
> 
> The av_assert2 calls should ease detecting broken demuxers.

have you tried a fuzzer ?
these assertions fail on fuzzed files

Assertion 0 failed at libavcodec/utils.c:4157
Aborted
Assertion !((unsigned)par->color_primaries > AVCOL_PRI_NB) failed at libavcodec/utils.c:4161

[...]
Andreas Cadhalpun Oct. 27, 2016, 8:43 p.m.
On 27.10.2016 22:14, Michael Niedermayer wrote:
> On Wed, Oct 26, 2016 at 01:59:59AM +0200, Andreas Cadhalpun wrote:
>> Note that the added asserts are triggered by *many* of my fuzzed samples.
>> I'm happy to write patches for these cases, if we achieve agreement
>> that the central check alone is insufficient.

Have you seen this comment?

>>  utils.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 80 insertions(+), 2 deletions(-)
>> 40a8bafecb6d289a4220a27ac411fbcac3204952  0001-avcodec-validate-codec-parameters.patch
>> From f371be7a027da3958e221b4dc88ad558c1489107 Mon Sep 17 00:00:00 2001
>> From: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
>> Date: Tue, 25 Oct 2016 01:45:27 +0200
>> Subject: [PATCH] avcodec: validate codec parameters
>>
>> This should reduce the impact of a broken demuxer (or API user) setting bogus
>> codec parameters.
>>
>> The av_assert2 calls should ease detecting broken demuxers.
> 
> have you tried a fuzzer ?
> these assertions fail on fuzzed files
> 
> Assertion 0 failed at libavcodec/utils.c:4157
> Aborted
> Assertion !((unsigned)par->color_primaries > AVCOL_PRI_NB) failed at libavcodec/utils.c:4161

As noted above, I'm well aware of that.
This just shows how many demuxers currently set bogus values...

Best regards,
Andreas

Patch hide | download patch | download mbox

From f371be7a027da3958e221b4dc88ad558c1489107 Mon Sep 17 00:00:00 2001
From: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
Date: Tue, 25 Oct 2016 01:45:27 +0200
Subject: [PATCH] avcodec: validate codec parameters

This should reduce the impact of a broken demuxer (or API user) setting bogus
codec parameters.

The av_assert2 calls should ease detecting broken demuxers.

Suggested-by: wm4
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
---
 libavcodec/utils.c | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 80 insertions(+), 2 deletions(-)

diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 87de15f..9773b0b 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -1243,6 +1243,7 @@  int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
     int ret = 0;
     AVDictionary *tmp = NULL;
     const AVPixFmtDescriptor *pixdesc;
+    AVCodecParameters *par = NULL;
 
     if (avcodec_is_open(avctx))
         return 0;
@@ -1259,8 +1260,14 @@  int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
     if (!codec)
         codec = avctx->codec;
 
-    if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
-        return AVERROR(EINVAL);
+    par = avcodec_parameters_alloc();
+    if (!par)
+        return AVERROR(ENOMEM);
+    /* check if the codec parameters in the context are valid */
+    ret = avcodec_parameters_from_context(par, avctx);
+    avcodec_parameters_free(&par);
+    if (ret < 0)
+        return ret;
 
     if (options)
         av_dict_copy(&tmp, *options, 0);
@@ -4124,6 +4131,66 @@  static void codec_parameters_reset(AVCodecParameters *par)
     par->level               = FF_LEVEL_UNKNOWN;
 }
 
+#define CHECK_PARAMETER(parameter, name, check) {                               \
+    av_assert2(!(check));                                                       \
+    if (check) {                                                                \
+        av_log(avctx, AV_LOG_ERROR, "Invalid " name " %d\n", par->parameter);   \
+        return AVERROR(EINVAL);                                                 \
+    }                                                                           \
+}
+
+static int codec_parameters_check(const AVCodecContext *codec, const AVCodecParameters *par)
+{
+    AVCodecContext *avctx = (AVCodecContext *)codec;
+    if (par->bit_rate < 0) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid bit rate %"PRId64"\n", par->bit_rate);
+        av_assert2(0);
+        return AVERROR(EINVAL);
+    }
+    CHECK_PARAMETER(bits_per_coded_sample, "bits per coded sample", par->bits_per_coded_sample < 0)
+    CHECK_PARAMETER(bits_per_raw_sample,   "bits per raw sample",   par->bits_per_raw_sample < 0)
+    CHECK_PARAMETER(extradata_size,        "extradata size",        par->extradata_size < 0 || par->extradata_size >= FF_MAX_EXTRADATA_SIZE)
+
+    switch (par->codec_type) {
+    case AVMEDIA_TYPE_VIDEO:
+        if ( (par->width || par->height) && av_image_check_size(par->width, par->height, 0, avctx) < 0) {
+            av_assert2(0);
+            return AVERROR(EINVAL);
+        }
+        CHECK_PARAMETER(color_range,     "color range",                     (unsigned)par->color_range > AVCOL_RANGE_NB)
+        CHECK_PARAMETER(color_primaries, "color primaries",                 (unsigned)par->color_primaries > AVCOL_PRI_NB)
+        CHECK_PARAMETER(color_trc,       "color transfer characteristics ", (unsigned)par->color_trc > AVCOL_PRI_NB)
+        CHECK_PARAMETER(color_space,     "color space",                     (unsigned)par->color_space > AVCOL_SPC_NB)
+        CHECK_PARAMETER(chroma_location, "chroma location",                 (unsigned)par->chroma_location > AVCHROMA_LOC_NB)
+        if (par->sample_aspect_ratio.num < 0 || par->sample_aspect_ratio.den < 0) {
+            av_log(avctx, AV_LOG_ERROR, "Invalid sample aspect ratio %d/%d\n",
+                   par->sample_aspect_ratio.num, par->sample_aspect_ratio.den);
+            av_assert2(0);
+            return AVERROR(EINVAL);
+        }
+        CHECK_PARAMETER(video_delay, "video delay", par->video_delay < 0)
+        break;
+    case AVMEDIA_TYPE_AUDIO:
+        CHECK_PARAMETER(format,           "sample format",      par->format < -1 || par->format > AV_SAMPLE_FMT_NB)
+        CHECK_PARAMETER(channels,         "number of channels", par->channels < 0)
+        CHECK_PARAMETER(sample_rate,      "sample rate",        par->sample_rate < 0)
+        CHECK_PARAMETER(block_align,      "block alignment",    par->block_align < 0)
+        CHECK_PARAMETER(frame_size,       "frame size",         par->frame_size < 0)
+        CHECK_PARAMETER(initial_padding,  "initial padding",    par->initial_padding < 0)
+        CHECK_PARAMETER(trailing_padding, "trailing padding",   par->trailing_padding < 0)
+        CHECK_PARAMETER(seek_preroll,     "seek preroll",       par->seek_preroll < 0)
+        break;
+    case AVMEDIA_TYPE_SUBTITLE:
+        if ((par->width || par->height) && av_image_check_size(par->width, par->height, 0, avctx) < 0) {
+            av_assert2(0);
+            return AVERROR(EINVAL);
+        }
+        break;
+    }
+    return 0;
+}
+
+
 AVCodecParameters *avcodec_parameters_alloc(void)
 {
     AVCodecParameters *par = av_mallocz(sizeof(*par));
@@ -4166,6 +4233,7 @@  int avcodec_parameters_copy(AVCodecParameters *dst, const AVCodecParameters *src
 int avcodec_parameters_from_context(AVCodecParameters *par,
                                     const AVCodecContext *codec)
 {
+    int ret;
     codec_parameters_reset(par);
 
     par->codec_type = codec->codec_type;
@@ -4217,12 +4285,22 @@  int avcodec_parameters_from_context(AVCodecParameters *par,
         par->extradata_size = codec->extradata_size;
     }
 
+    ret = codec_parameters_check(codec, par);
+    if (ret < 0) {
+        codec_parameters_reset(par);
+        return ret;
+    }
+
     return 0;
 }
 
 int avcodec_parameters_to_context(AVCodecContext *codec,
                                   const AVCodecParameters *par)
 {
+    int ret = codec_parameters_check(codec, par);
+    if (ret < 0)
+        return ret;
+
     codec->codec_type = par->codec_type;
     codec->codec_id   = par->codec_id;
     codec->codec_tag  = par->codec_tag;
-- 
2.9.3