[Spice-devel] [PATCH usbredir] Avoid format truncation warnings on newer gcc

[Frediano Ziglio]

> 
> For some reason, newer versions  of gcc (e.g. 7.1.1 in fedora 26) print
> a warning about format truncation even when using snprintf:
> 
>   CC       usbredirparser.lo
> ../../usbredirparser/usbredirparser.c: In function ‘usbredirparser_do_read’:
> ../../usbredirparser/usbredirparser.c:270:33: error: ‘%s’ directive output
> may be truncated writing up to 287 bytes into a region of size 64
> [-Werror=format-truncation=]
>      snprintf(buf, sizeof(buf), "%s", hello->version);
>                                  ^~
> ../../usbredirparser/usbredirparser.c:270:5: note: ‘snprintf’ output between
> 1 and 288 bytes into a destination of size 64
>      snprintf(buf, sizeof(buf), "%s", hello->version);
>      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Because type_header is a 288-byte array that is cast to a 'struct
> usb_redir_hello_header' and passed to the function, gcc apaprently believes

typo: apaprently -> apparently

> that hello->version might be up to 288 bytes and warns about format
> truncation.
> To avoid this warning, simply use strncpy (and ensure that the last byte is
> NULL).
> ---
>  usbredirparser/usbredirparser.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/usbredirparser/usbredirparser.c
> b/usbredirparser/usbredirparser.c
> index 5dfeb9e..8f239cc 100644
> --- a/usbredirparser/usbredirparser.c
> +++ b/usbredirparser/usbredirparser.c
> @@ -267,7 +267,8 @@ static void usbredirparser_handle_hello(struct
> usbredirparser *parser_pub,
>  
>      /* In case hello->version is not 0 terminated (which would be a protocol
>         violation)_ */
> -    snprintf(buf, sizeof(buf), "%s", hello->version);
> +    strncpy(buf, hello->version, sizeof(buf));
> +    buf[sizeof(buf)-1] = '\0';
>  
>      memset(parser->peer_caps, 0, sizeof(parser->peer_caps));
>      if (data_len > sizeof(parser->peer_caps)) {

Beside the typo,

Acked-by: Frediano Ziglio <fziglio at redhat.com>

Frediano