[FFmpeg-devel] [PATCH]lavf/matroskadec: Do not use strncat() to limit copying a one-char constant

[Mark Thompson]

On 10/12/2018 00:57, Carl Eugen Hoyos wrote:
> 2018-12-09 19:03 GMT+01:00, Mark Thompson <sw at jkqxz.net>:
>> On 06/12/2018 22:26, Carl Eugen Hoyos wrote:
>>> Hi!
>>>
>>> Attached patch silences a new gcc warning, alternative would be to
>>> disable the warning.
>>>
>>> Please comment, Carl Eugen
>>>
>>>
>>> From dd49cddc6fad136222d4a168301059d55fea4a4c Mon Sep 17 00:00:00 2001
>>> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
>>> Date: Thu, 6 Dec 2018 23:23:12 +0100
>>> Subject: [PATCH] lavf/matroskadec: Do not use strncat() to limit copying a
>>>  one-char constant.
>>>
>>> Silences a warning:
>>> libavformat/matroskadec.c: In function 'webm_dash_manifest_cues':
>>> libavformat/matroskadec.c:3947:13: warning: 'strncat' specified bound 1
>>> equals source length [-Wstringop-overflow=]
>>>              strncat(buf, ",", 1);
>>>              ^~~~~~~~~~~~~~~~~~~~
>>> ---
>>>  libavformat/matroskadec.c |    2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
>>> index 2daa1db..df820b4 100644
>>> --- a/libavformat/matroskadec.c
>>> +++ b/libavformat/matroskadec.c
>>> @@ -3944,7 +3944,7 @@ static int webm_dash_manifest_cues(AVFormatContext
>>> *s, int64_t init_range)
>>>          }
>>>          end += ret;
>>>          if (i != s->streams[0]->nb_index_entries - 1) {
>>> -            strncat(buf, ",", 1);
>>> +            strcat(buf, ",");
>>>              end++;
>>>          }
>>>      }
>>> --
>>> 1.7.10.4
>>>
>>
>> LGTM.
>>
>> (Optional: perhaps nicer to remove that code fragment with the str(n?)cat
>> completely by including the comma in the snprintf above, as '"%s", i !=
>> s->streams[0]->nb_index_entries - 1 ? "," : ""'?)
> 
> New patch attached.
> 
> Please review, Carl Eugen
> 
> 
> From 082bce9706a4c326187ae543d8b8aa93424c48b0 Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
> Date: Mon, 10 Dec 2018 01:55:15 +0100
> Subject: [PATCH] lavf/matroskadec: Do not use strncat() to limit copying a
>  one-char constant.
> 
> Instead add the character to the snprintf above as suggested by Mark.
> 
> Silences a warning:
> libavformat/matroskadec.c: In function 'webm_dash_manifest_cues':
> libavformat/matroskadec.c:3947:13: warning: 'strncat' specified bound 1 equals source length [-Wstringop-overflow=]
>              strncat(buf, ",", 1);
>              ^~~~~~~~~~~~~~~~~~~~
> ---
>  libavformat/matroskadec.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
> index 2daa1db..4ad99db 100644
> --- a/libavformat/matroskadec.c
> +++ b/libavformat/matroskadec.c
> @@ -3936,17 +3936,14 @@ static int webm_dash_manifest_cues(AVFormatContext *s, int64_t init_range)
>      strcpy(buf, "");
>      for (i = 0; i < s->streams[0]->nb_index_entries; i++) {
>          int ret = snprintf(buf + end, 20,
> -                           "%" PRId64, s->streams[0]->index_entries[i].timestamp);
> +                           "%" PRId64"%s", s->streams[0]->index_entries[i].timestamp,
> +                           i != s->streams[0]->nb_index_entries - 1 ? "," : "");
>          if (ret <= 0 || (ret == 20 && i ==  s->streams[0]->nb_index_entries - 1)) {
>              av_log(s, AV_LOG_ERROR, "timestamp too long.\n");
>              av_free(buf);
>              return AVERROR_INVALIDDATA;
>          }
>          end += ret;
> -        if (i != s->streams[0]->nb_index_entries - 1) {
> -            strncat(buf, ",", 1);
> -            end++;
> -        }
>      }
>      av_dict_set(&s->streams[0]->metadata, CUE_TIMESTAMPS, buf, 0);
>      av_free(buf);
> -- 
> 1.7.10.4

Yep, LGTM.

Thanks,

- Mark