Re: [dpdk-dev] [PATCH 3/4] examples/mp_server: fix snprintf overflow

[Stephen Hemminger <stephen@networkplumber.org>]

On Fri, 14 Aug 2020 12:00:44 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> When producing a printable mac address the buffer was appropriately sized
> for holding the mac address exactly, but the actual snprintf included a
> '\n' character at the end, which means that the snprintf technically is
> getting truncated i.e. the \n would not be added due to lack of space.
> This gets flagged as a problem by modern versions of gcc, e.g. on Ubuntu
> 20.04.
> 
> main.c:77:37: warning: ‘__builtin___snprintf_chk’ output truncated before the last format character [-Wformat-truncation=]
>    77 |     "%02x:%02x:%02x:%02x:%02x:%02x\n",
>       |                                     ^
> 
> Since the \n is getting stripped anyway, we can fix the issue by just
> removing it from the printf string.
> 
> Fixes: af75078fece3 ("first public release")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  examples/multi_process/client_server_mp/mp_server/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/examples/multi_process/client_server_mp/mp_server/main.c b/examples/multi_process/client_server_mp/mp_server/main.c
> index 280dab8672..af5af672c3 100644
> --- a/examples/multi_process/client_server_mp/mp_server/main.c
> +++ b/examples/multi_process/client_server_mp/mp_server/main.c
> @@ -74,7 +74,7 @@ get_printable_mac_addr(uint16_t port)
>  			return err_address;
>  		}
>  		snprintf(addresses[port], sizeof(addresses[port]),
> -				"%02x:%02x:%02x:%02x:%02x:%02x\n",
> +				"%02x:%02x:%02x:%02x:%02x:%02x",
>  				mac.addr_bytes[0], mac.addr_bytes[1], mac.addr_bytes[2],
>  				mac.addr_bytes[3], mac.addr_bytes[4], mac.addr_bytes[5]);
>  	}

Please convert to rte_ether_format_addr() instead of local hard coded format.