[FFmpeg-devel] [PATCH V3] lavc/golomb: Fix UE golomb overwrite issue.

[Jun Zhao]

On 2017/6/8 18:02, Mark Thompson wrote:
> On 08/06/17 01:29, Jun Zhao wrote:
>> V3: Clean the code logic base on Michael's review.
>> V2: Add Add set_ue_golomb_long() to support 32bits UE golomb and update the unit test.
>>
>> From 4de3e0c30af7bc1901562000eda018a6d6849292 Mon Sep 17 00:00:00 2001
>> From: Jun Zhao <jun.zhao at intel.com>
>> Date: Fri, 2 Jun 2017 15:05:49 +0800
>> Subject: [PATCH V3] lavc/golomb: Fix UE golomb overwrite issue.
>>
>> put_bits just support write up to 31 bits, when write 32 bit in
>> put_bits, it's will overwrite the bit buffer, because the default
>> assert level is 0, the av_assert2(n <= 31 && value < (1U << n))
>> in put_bits can not be trigger runtime. Add set_ue_golomb_long()
>> to support 32bits UE golomb.
>>
>> Signed-off-by: Jun Zhao <jun.zhao at intel.com>
>> ---
>>  libavcodec/golomb.h       | 17 ++++++++++++++++-
>>  libavcodec/put_bits.h     | 35 +++++++++++++++++++++++++++++++++++
>>  libavcodec/tests/golomb.c | 19 +++++++++++++++++++
>>  3 files changed, 70 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavcodec/golomb.h b/libavcodec/golomb.h
>> index 0833aff468..cba4861b10 100644
>> --- a/libavcodec/golomb.h
>> +++ b/libavcodec/golomb.h
>> @@ -458,7 +458,7 @@ static inline int get_te(GetBitContext *s, int r, char *file, const char *func,
>>  #endif /* TRACE */
>>  
>>  /**
>> - * write unsigned exp golomb code.
>> + * write unsigned exp golomb code. 2^16-2 at most.
>>   */
>>  static inline void set_ue_golomb(PutBitContext *pb, int i)
>>  {
>> @@ -473,6 +473,21 @@ static inline void set_ue_golomb(PutBitContext *pb, int i)
>>  }
>>  
>>  /**
>> + * write unsigned exp golomb code. 2^32-2 at most.
>> + */
>> +static inline void set_ue_golomb_long(PutBitContext *pb, uint32_t i)
>> +{
>> +    av_assert2(i <= (0xffffffff - 2));
> 
> That's not 2^32 - 2.  Maybe use UINT32_MAX - 1
Your are right, will fix in the next version.

>> +
>> +    if (i < 256)
>> +        put_bits(pb, ff_ue_golomb_len[i], i + 1);
>> +    else {
>> +        int e = av_log2(i + 1);
>> +        put_bits64(pb, 2 * e + 1, i + 1);
>> +    }
>> +}
> 
> Please don't add a new function, just extend the existing one.  set_ue_golomb() is not used in any place where minor ricing is of any value, and having another function will only be confusing over which to use (or, more likely, people will always use the long version in order to avoid thinking about it just like they do with get_ue_golomb() - cf. "grep get_ue_golomb libavcodec/hevc*").

We have get_ue_golomb/get_ue_golomb_long/get_ue_golomb_31/..., I think add new set_ue_golomb_long is Ok,
the caller need to make the decision base on the value range even set_ue_golomb_long can cover the set_ue_golomb.

> 
>> +
>> +/**
>>   * write truncated unsigned exp golomb code.
>>   */
>>  static inline void set_te_golomb(PutBitContext *pb, int i, int range)
>> diff --git a/libavcodec/put_bits.h b/libavcodec/put_bits.h
>> index 68ed391195..06f0ebbeba 100644
>> --- a/libavcodec/put_bits.h
>> +++ b/libavcodec/put_bits.h
>> @@ -221,6 +221,41 @@ static void av_unused put_bits32(PutBitContext *s, uint32_t value)
>>  }
>>  
>>  /**
>> + * Write up to 64 bits into a bitstream.
>> + */
>> +static inline void put_bits64(PutBitContext *s, int n, uint64_t value)
> 
> put_bits32() writes exactly 32 bits, so it sounds like put_bits64() will write exactly 64 bits.  I'm not sure what the function should be called, but not that.
> 

For the function name, I can't find other good name short time. :(
>> +{
>> +    av_assert2(n <= 64 && value < (1UL << n));
> 
> 1UL is 32-bit on ILP32 platforms, so 1 << n is zero for n > 31 and the assert will always fail.
> 
> Maybe "av_assert2(n == 64 || (n < 64 && value < UINT64_C(1) << n))"?
> 

Thanks again.

>> +
>> +    if (n < 32)
>> +        put_bits(s, n, value);
>> +    else if (n == 32)
>> +        put_bits32(s, value);
>> +    else if (n < 64) {
>> +        uint32_t lo = value & 0xffffffff;
>> +        uint32_t hi = value >> 32;
>> +#ifdef BITSTREAM_WRITER_LE
>> +        put_bits32(s, lo);
>> +        put_bits(s, n - 32, hi);
>> +#else
>> +        put_bits(s, n - 32, hi);
>> +        put_bits32(s, lo);
>> +#endif
>> +    } else {
>> +        uint32_t lo = value & 0xffffffff;
>> +        uint32_t hi = value >> 32;
>> +#ifdef BITSTREAM_WRITER_LE
>> +        put_bits32(s, lo);
>> +        put_bits32(s, hi);
>> +#else
>> +        put_bits32(s, hi);
>> +        put_bits32(s, lo);
>> +#endif
>> +
>> +    }
>> +}
>> +
>> +/**
>>   * Return the pointer to the byte where the bitstream writer will put
>>   * the next bit.
>>   */
>> diff --git a/libavcodec/tests/golomb.c b/libavcodec/tests/golomb.c
>> index 965367b7be..85b8a9390b 100644
>> --- a/libavcodec/tests/golomb.c
>> +++ b/libavcodec/tests/golomb.c
>> @@ -21,6 +21,7 @@
>>  #include <stdint.h>
>>  #include <stdio.h>
>>  
>> +#include "libavutil/internal.h"
>>  #include "libavutil/mem.h"
>>  
>>  #include "libavcodec/get_bits.h"
>> @@ -76,6 +77,24 @@ int main(void)
>>          }
>>      }
>>  
>> +#define EXTEND_L(i) ((i) << 4 | (i) & 15)
>> +    init_put_bits(&pb, temp, SIZE);
>> +    for (i = 0; i < COUNT; i++)
>> +        set_ue_golomb_long(&pb, EXTEND_L(i));
>> +    flush_put_bits(&pb);
>> +
>> +    init_get_bits(&gb, temp, 8 * SIZE);
>> +    for (i = 0; i < COUNT; i++) {
>> +        int j, s = show_bits_long(&gb, 32);
>> +
>> +        j = get_ue_golomb_long(&gb);
>> +        if (j != EXTEND_L(i)) {
>> +            fprintf(stderr, "get_ue_golomb_long: expected %d, got %d. "
>> +                    "bits: %8x\n", EXTEND_L(i), j, s);
>> +            ret = 1;
>> +        }
>> +    }
>> +
>>      init_put_bits(&pb, temp, SIZE);
>>      for (i = 0; i < COUNT; i++)
>>          set_se_golomb(&pb, i - COUNT / 2);
>> -- 
>> 2.11.0
>>
> 
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