James Almer:
> On 2/26/2024 8:27 PM, Andreas Rheinhardt wrote:
>> It is undefined behaviour.
>> Fixes many failed tests with UBSan and GCC 13 like
>> "src/libavformat/mov.c:4229:44: runtime error: store to address
>> 0x5572abe20f80 with insufficient space for an object of type 'struct
>> MOVIndexRange'"
>> (The line number does not refer to the line where &entry[-1]
>> is assigned.)
>>
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com>
>> ---
>> libavformat/mov.c | 11 ++++++-----
>> 1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>> index 71e8f7ae8f..97caaa7723 100644
>> --- a/libavformat/mov.c
>> +++ b/libavformat/mov.c
>> @@ -4022,7 +4022,7 @@ static void mov_fix_index(MOVContext *mov,
>> AVStream *st)
>> int num_discarded_begin = 0;
>> int first_non_zero_audio_edit = -1;
>> int packet_skip_samples = 0;
>> - MOVIndexRange *current_index_range;
>> + MOVIndexRange *current_index_range = NULL;
>> int found_keyframe_after_edit = 0;
>> int found_non_empty_edit = 0;
>> @@ -4038,7 +4038,6 @@ static void mov_fix_index(MOVContext *mov,
>> AVStream *st)
>> return;
>> }
>> msc->current_index_range = msc->index_ranges;
>> - current_index_range = msc->index_ranges - 1;
>> // Clean AVStream from traces of old index
>> sti->index_entries = NULL;
>> @@ -4225,8 +4224,9 @@ static void mov_fix_index(MOVContext *mov,
>> AVStream *st)
>> }
>> // Update the index ranges array
>> - if (current_index_range < msc->index_ranges || index !=
>> current_index_range->end) {
>> - current_index_range++;
>> + if (!current_index_range || index !=
>> current_index_range->end) {
>> + current_index_range = current_index_range ?
>> current_index_range + 1
>> + :
>> msc->index_ranges;
>> current_index_range->start = index;
>> }
>> current_index_range->end = index + 1;
>> @@ -4289,7 +4289,8 @@ static void mov_fix_index(MOVContext *mov,
>> AVStream *st)
>> av_freep(&frame_duration_buffer);
>> // Null terminate the index ranges array
>> - current_index_range++;
>> + current_index_range = current_index_range ? current_index_range + 1
>> + : msc->index_ranges;
>> current_index_range->start = 0;
>> current_index_range->end = 0;
>> msc->current_index = msc->index_ranges[0].start;
>
> Can't test if this fixes the UB, but the changes lgtm.
It does:
https://fate.ffmpeg.org/report.cgi?slot=x86_64-archlinux-gcc-ubsan&time=20240227105551
- Andreas
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