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

[Kunwu Chan]

Thanks for your reply.

On 2024/8/14 18:28, NeilBrown wrote:
> On Wed, 14 Aug 2024, kunwu.chan@xxxxxxxxx wrote:
> > From: Kunwu Chan <chentao@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >   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.
My negligence.
> 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.
I'm thinking  about use a dynamic space alloc method like kasprintf to 
avoid space waste.
> 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.

Thank you for the detailed explanation. I read the 
xprt_create_transport,  the RPC_MAXNETNAMELEN

is only use to xprt_create_transport .

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

Whether we could check the sun->sun_path length before using snprintf?  
The array size should smaller

than  the minimum of sun->sun_path and RPC_MAXNETNAMELEN.

Or use the dynamic space allocate method to save space.

> Thanks,
> NeilBrown
>
>
> >   	struct rpc_clnt *clnt;
> >   	int i;
> >   
> > --
> > 2.40.1
--
Thanks,
  Kunwu.Chan