Re: [FFmpeg-devel] [PATCH] avformat/hls: use av_strlcopy instead of strncpy

[Leo Izen <leo.izen@gmail.com>]

On 10/26/23 07:32, Andreas Rheinhardt wrote:
> 
> This case can't happen here, because it only copies
> "sizeof(rend->language) - langlen - 2" bytes at most from position where
> sizeof(rend->language) - langlen - 1 are available, so the initial
> trailing \0 never gets touched. You did not touch the size part of the
> call, so you effectively only use sizeof(rend->language) - 1 bytes of
> the buffer, thereby making the truncation issue worse. And even if you
> fixed this part, you would still just have silenced the truncation
> instead of fixing it.
> 
> - Andreas
> 

Truncation can happen if info->assoc_language is very long, i.e. uses 
the full buffer (63 chars plus a 64th for nul).

In that case, strncpy will truncate, but because there's a -2 in the 
size argument, instead of -1, the resulting buffer will still be 
nul-terminated. The compiler doesn't know this, so it produces a warning.

It seems the appropriate fix here is to change strncpy to av_strlcpy but
also change the -2 to a -1. This will produce identical behavior to 
before, but it won't cause the compiler to produce a warning that the 
string might not be nul-terminated (cause it will always be).

- Leo Izen (Traneptora)

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