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

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Message-id: <172372194692.6062.4519803974558688969@noble.neil.brown.name>
Date: Thu, 15 Aug 2024 21:39:06 +1000
From: "NeilBrown" <neilb@...e.de>
To: "Kunwu Chan" <kunwu.chan@...ux.dev>
Cc: trondmy@...nel.org, anna@...nel.org, chuck.lever@...cle.com,
 jlayton@...nel.org, kolga@...app.com, Dai.Ngo@...cle.com, tom@...pey.com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
 linux-nfs@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, "Kunwu Chan" <chentao@...inos.cn>
Subject: Re: [PATCH] SUNRPC: Fix -Wformat-truncation warning

On Thu, 15 Aug 2024, Kunwu Chan wrote:
> Thanks for your reply.
> 
> On 2024/8/14 18:28, NeilBrown wrote:
> > On Wed, 14 Aug 2024, kunwu.chan@...ux.dev wrote:
> >> From: Kunwu Chan <chentao@...inos.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@...inos.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.
> 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.

I think that dynamically allocating space is not a good idea.  It means
you have to handle failure which is just a waste of code.

I'd suggest simply changing the array to RPC_MAXNETNAMELEN.

NeilBrown



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