Re: [PATCH] SUNRPC: Fix -Wformat-truncation warning

NeilBrown
2024-08-14T10:28:46Z

On Wed, 14 Aug 2024, kunwu.chan@linux.dev wrote:
> From: Kunwu Chan <chentao@kylinos.cn>
>
> Increase size of the servername array to avoid truncated output warning.
>
> net/sunrpc/clnt.c:582:75: error：‘%s’ directive output may be truncated
> writing up to 107 bytes into a region of size 48
> [-Werror=format-truncation=]
> 582 | snprintf(servername, sizeof(servername), "%s",
> | ^~
>
> net/sunrpc/clnt.c:582:33: note:‘snprintf’ output
> between 1 and 108 bytes into a destination of size 48
> 582 | snprintf(servername, sizeof(servername), "%s",
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 583 | sun->sun_path);
>
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
> ---
> net/sunrpc/clnt.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index 09f29a95f2bc..874085f3ed50 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -546,7 +546,7 @@ struct rpc_clnt *rpc_create(struct rpc_create_args *args)
> .connect_timeout = args->connect_timeout,
> .reconnect_timeout = args->reconnect_timeout,
> };
> - char servername[48];
> + char servername[108];

If we choose this approach to removing the warning, then we should use
UNIX_PATH_MAX rather than 108.

However the longest server name copied in here will in practice be
/var/run/rpcbind.sock

so the extra 60 bytes on the stack is wasted ... maybe that doesn't
matter.

The string is only used by xprt_create_transport() which requires it to
be less than RPC_MAXNETNAMELEN - which is 256.
So maybe that would be a better value to use for the array size .... if
we assume that stack space isn't a problem.

What ever number we use, I'd rather it was a defined constant, and not
an apparently arbitrary number.

Thanks,
NeilBrown

> struct rpc_clnt *clnt;
> int i;
>
> --
> 2.40.1
>
>