[FFmpeg-devel] [PATCH 1/2] avcodec/v4l2_m2m: Avoid using intermediate buffer

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Up until now, v4l2_m2m would write via snprintf() into an intermediate
> buffer and then copy from there (via strncpy()) to the end buffer. This
> commit changes this by removing the intermediate buffer.
> 
> The call to strncpy() was actually of the form strncpy(dst, src,
> strlen(src) + 1) which is unsafe in general, but safe in this instance
> because dst and src were both of the same size and src was a proper
> zero-terminated string. But this nevertheless led to a compiler warning
> "‘strncpy’ specified bound depends on the length of the source argument
> [-Wstringop-overflow=]" in GCC 9.2. strlen() was unnecessary anyway.
> 
> Reviewed-by: Andriy Gelman <andriy.gelman at gmail.com>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
> Thanks to Andriy for testing and reviewing.
> 
>  libavcodec/v4l2_m2m.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/v4l2_m2m.c b/libavcodec/v4l2_m2m.c
> index 2d21f910bc..e48b3a8ccf 100644
> --- a/libavcodec/v4l2_m2m.c
> +++ b/libavcodec/v4l2_m2m.c
> @@ -358,7 +358,6 @@ int ff_v4l2_m2m_codec_init(V4L2m2mPriv *priv)
>  {
>      int ret = AVERROR(EINVAL);
>      struct dirent *entry;
> -    char node[PATH_MAX];
>      DIR *dirp;
>  
>      V4L2m2mContext *s = priv->context;
> @@ -372,9 +371,8 @@ int ff_v4l2_m2m_codec_init(V4L2m2mPriv *priv)
>          if (strncmp(entry->d_name, "video", 5))
>              continue;
>  
> -        snprintf(node, sizeof(node), "/dev/%s", entry->d_name);
> -        av_log(s->avctx, AV_LOG_DEBUG, "probing device %s\n", node);
> -        strncpy(s->devname, node, strlen(node) + 1);
> +        snprintf(s->devname, sizeof(s->devname), "/dev/%s", entry->d_name);
> +        av_log(s->avctx, AV_LOG_DEBUG, "probing device %s\n", s->devname);
>          ret = v4l2_probe_driver(s);
>          if (!ret)
>              break;
> @@ -389,7 +387,7 @@ int ff_v4l2_m2m_codec_init(V4L2m2mPriv *priv)
>          return ret;
>      }
>  
> -    av_log(s->avctx, AV_LOG_INFO, "Using device %s\n", node);
> +    av_log(s->avctx, AV_LOG_INFO, "Using device %s\n", s->devname);
>  
>      return v4l2_configure_contexts(s);
>  }
> 

Ping for this patchset.

- Andreas