[FFmpeg-devel] [PATCH v2] avcodec/hevc_ps: fix the problem of memcmp losing effectiveness

[FFmpeg-devel] [PATCH v2] avcodec/hevc_ps: fix the problem of memcmp losing effectiveness

[tong1.wu-at-intel.com]

From: Tong Wu <tong1.wu@intel.com>

HEVCHdrParams* receives a pointer which points to a dynamically
allocated memory block. It causes the memcmp always returning 1.
Add a function to do the comparision. A condition is also added to
avoid malloc(0).

Signed-off-by: Tong Wu <tong1.wu@intel.com>
---
 libavcodec/hevc_ps.c | 22 ++++++++++++++++++----
 libavcodec/hevc_ps.h |  4 +++-
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/libavcodec/hevc_ps.c b/libavcodec/hevc_ps.c
index cbef3ef4cd..d3c589ec24 100644
--- a/libavcodec/hevc_ps.c
+++ b/libavcodec/hevc_ps.c
@@ -449,6 +449,18 @@ static void uninit_vps(FFRefStructOpaque opaque, void *obj)
     av_freep(&vps->hdr);
 }
 
+static int compare_vps(const HEVCVPS *vps1, const HEVCVPS *vps2)
+{
+    if (!vps1->hdr && !vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)))
+        return 1;
+
+    if (vps1->hdr && vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)) &&
+        !memcmp(vps1->hdr, vps2->hdr, vps1->vps_num_hrd_parameters * sizeof(*vps1->hdr)))
+        return 1;
+
+    return 0;
+}
+
 int ff_hevc_decode_nal_vps(GetBitContext *gb, AVCodecContext *avctx,
                            HEVCParamSets *ps)
 {
@@ -545,9 +557,11 @@ int ff_hevc_decode_nal_vps(GetBitContext *gb, AVCodecContext *avctx,
             goto err;
         }
 
-        vps->hdr = av_calloc(vps->vps_num_hrd_parameters, sizeof(*vps->hdr));
-        if (!vps->hdr)
-            goto err;
+        if (vps->vps_num_hrd_parameters) {
+            vps->hdr = av_calloc(vps->vps_num_hrd_parameters, sizeof(*vps->hdr));
+            if (!vps->hdr)
+                goto err;
+        }
 
         for (i = 0; i < vps->vps_num_hrd_parameters; i++) {
             int common_inf_present = 1;
@@ -569,7 +583,7 @@ int ff_hevc_decode_nal_vps(GetBitContext *gb, AVCodecContext *avctx,
     }
 
     if (ps->vps_list[vps_id] &&
-        !memcmp(ps->vps_list[vps_id], vps, sizeof(*vps))) {
+        compare_vps(ps->vps_list[vps_id], vps)) {
         ff_refstruct_unref(&vps);
     } else {
         remove_vps(ps, vps_id);
diff --git a/libavcodec/hevc_ps.h b/libavcodec/hevc_ps.h
index cc75aeb8d3..0d8eaf2b3e 100644
--- a/libavcodec/hevc_ps.h
+++ b/libavcodec/hevc_ps.h
@@ -153,7 +153,6 @@ typedef struct PTL {
 
 typedef struct HEVCVPS {
     unsigned int vps_id;
-    HEVCHdrParams *hdr;
 
     uint8_t vps_temporal_id_nesting_flag;
     int vps_max_layers;
@@ -175,6 +174,9 @@ typedef struct HEVCVPS {
 
     uint8_t data[4096];
     int data_size;
+    /* Put this at the end of the structure to make it easier to calculate the
+     * size before this pointer, which is used for memcmp */
+    HEVCHdrParams *hdr;
 } HEVCVPS;
 
 typedef struct ScalingList {
-- 
2.41.0.windows.1

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Re: [FFmpeg-devel] [PATCH v2] avcodec/hevc_ps: fix the problem of memcmp losing effectiveness

[James Almer]

On 3/29/2024 12:13 PM, tong1.wu-at-intel.com@ffmpeg.org wrote:
> From: Tong Wu <tong1.wu@intel.com>
> 
> HEVCHdrParams* receives a pointer which points to a dynamically
> allocated memory block. It causes the memcmp always returning 1.
> Add a function to do the comparision. A condition is also added to
> avoid malloc(0).
> 
> Signed-off-by: Tong Wu <tong1.wu@intel.com>
> ---
>   libavcodec/hevc_ps.c | 22 ++++++++++++++++++----
>   libavcodec/hevc_ps.h |  4 +++-
>   2 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/hevc_ps.c b/libavcodec/hevc_ps.c
> index cbef3ef4cd..d3c589ec24 100644
> --- a/libavcodec/hevc_ps.c
> +++ b/libavcodec/hevc_ps.c
> @@ -449,6 +449,18 @@ static void uninit_vps(FFRefStructOpaque opaque, void *obj)
>       av_freep(&vps->hdr);
>   }
>   
> +static int compare_vps(const HEVCVPS *vps1, const HEVCVPS *vps2)
> +{
> +    if (!vps1->hdr && !vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)))
> +        return 1;
> +
> +    if (vps1->hdr && vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)) &&
> +        !memcmp(vps1->hdr, vps2->hdr, vps1->vps_num_hrd_parameters * sizeof(*vps1->hdr)))
> +        return 1;
> +
> +    return 0;
> +}

Something like this should be simpler

> +static int compare_vps(const HEVCVPS *vps1, const HEVCVPS *vps2)
> +{
> +    if (!memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)))
> +        return !vps1->vps_num_hrd_parameters ||
> +               !memcmp(vps1->hdr, vps2->hdr, vps1->vps_num_hrd_parameters * sizeof(*vps1->hdr));
> +
> +    return 0;
> +}

If vps1 is equal to vps2 up to hdr, then vps_num_hrd_parameters will be 
the same in both and you can safely just go ahead with the memcmp for hdr.
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Re: [FFmpeg-devel] [PATCH v2] avcodec/hevc_ps: fix the problem of memcmp losing effectiveness

[Wu, Tong1]

>From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of James
>Almer
>Sent: Friday, March 29, 2024 11:18 PM
>To: ffmpeg-devel@ffmpeg.org
>Subject: Re: [FFmpeg-devel] [PATCH v2] avcodec/hevc_ps: fix the problem of
>memcmp losing effectiveness
>
>On 3/29/2024 12:13 PM, tong1.wu-at-intel.com@ffmpeg.org wrote:
>> From: Tong Wu <tong1.wu@intel.com>
>>
>> HEVCHdrParams* receives a pointer which points to a dynamically
>> allocated memory block. It causes the memcmp always returning 1.
>> Add a function to do the comparision. A condition is also added to
>> avoid malloc(0).
>>
>> Signed-off-by: Tong Wu <tong1.wu@intel.com>
>> ---
>>   libavcodec/hevc_ps.c | 22 ++++++++++++++++++----
>>   libavcodec/hevc_ps.h |  4 +++-
>>   2 files changed, 21 insertions(+), 5 deletions(-)
>>
>> diff --git a/libavcodec/hevc_ps.c b/libavcodec/hevc_ps.c
>> index cbef3ef4cd..d3c589ec24 100644
>> --- a/libavcodec/hevc_ps.c
>> +++ b/libavcodec/hevc_ps.c
>> @@ -449,6 +449,18 @@ static void uninit_vps(FFRefStructOpaque opaque,
>void *obj)
>>       av_freep(&vps->hdr);
>>   }
>>
>> +static int compare_vps(const HEVCVPS *vps1, const HEVCVPS *vps2)
>> +{
>> +    if (!vps1->hdr && !vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS,
>hdr)))
>> +        return 1;
>> +
>> +    if (vps1->hdr && vps2->hdr && !memcmp(vps1, vps2, offsetof(HEVCVPS,
>hdr)) &&
>> +        !memcmp(vps1->hdr, vps2->hdr, vps1->vps_num_hrd_parameters *
>sizeof(*vps1->hdr)))
>> +        return 1;
>> +
>> +    return 0;
>> +}
>
>Something like this should be simpler
>
>> +static int compare_vps(const HEVCVPS *vps1, const HEVCVPS *vps2)
>> +{
>> +    if (!memcmp(vps1, vps2, offsetof(HEVCVPS, hdr)))
>> +        return !vps1->vps_num_hrd_parameters ||
>> +               !memcmp(vps1->hdr, vps2->hdr, vps1->vps_num_hrd_parameters *
>sizeof(*vps1->hdr));
>> +
>> +    return 0;
>> +}
>
>If vps1 is equal to vps2 up to hdr, then vps_num_hrd_parameters will be
>the same in both and you can safely just go ahead with the memcmp for hdr.

That makes sense. Thank you.

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>ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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