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

Kunwu Chan
2024-08-15T08:30:45Z

Thanks for your reply.

On 2024/8/14 18:28, NeilBrown wrote:
> 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.
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