netdev - Re: [PATCH net-next] ibmvnic: fix kernel build warning in strncpy

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Message-ID: <CAOhMmr4Kumw7XCUG1RaN9U+nYR_a6NcY6Z28FnhswV2+ceQuhw@mail.gmail.com>
Date:   Fri, 11 Jun 2021 13:36:55 -0500
From:   Lijun Pan <lijunp213@...il.com>
To:     Shannon Nelson <snelson@...sando.io>
Cc:     Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] ibmvnic: fix kernel build warning in strncpy

On Fri, Jun 11, 2021 at 11:28 AM Shannon Nelson <snelson@...sando.io> wrote:
>
> On 6/11/21 9:05 AM, Lijun Pan wrote:
> > drivers/net/ethernet/ibm/ibmvnic.c: In function ‘handle_vpd_rsp’:
> > drivers/net/ethernet/ibm/ibmvnic.c:4393:3: warning: ‘strncpy’ output truncated before terminating nul copying 3 bytes from a string of the same length [-Wstringop-truncation]
> >   4393 |   strncpy((char *)adapter->fw_version, "N/A", 3 * sizeof(char));
> >        |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Signed-off-by: Lijun Pan <lijunp213@...il.com>
> > ---
> >   drivers/net/ethernet/ibm/ibmvnic.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
> > index 497f1a7da70b..2675b2301ed7 100644
> > --- a/drivers/net/ethernet/ibm/ibmvnic.c
> > +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> > @@ -4390,7 +4390,7 @@ static void handle_vpd_rsp(union ibmvnic_crq *crq,
> >
> >   complete:
> >       if (adapter->fw_version[0] == '\0')
> > -             strncpy((char *)adapter->fw_version, "N/A", 3 * sizeof(char));
> > +             memcpy((char *)adapter->fw_version, "N/A", 3 * sizeof(char));
> >       complete(&adapter->fw_done);
> >   }
> >
>
> This doesn't fix the real problem.  The error message is saying that
> there is no string terminating '\0' byte getting set after the "N/A"
> string, meaning that there could be garbage in the buffer after the
> string that could allow for surprising and bad things to happen when
> that string is used later, including buffer overruns that can cause
> stack smash or other memory munging.
>
> Better would be to use strlcpy() with a limiter of
> sizeof(adapter->fw_version).
>
> sln

Thanks for the tip. I looked up both strscpy and strlcpy. It seems nowadays
strscpy is preferred.