linux-kernel - Re: [PATCH 4.19 079/422] i40e: use correct length for strncpy

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Message-ID: <20191121103504.GC26882@amd>
Date:   Thu, 21 Nov 2019 11:35:04 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mitch Williams <mitch.a.williams@...el.com>,
        Andrew Bowers <andrewx.bowers@...el.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 079/422] i40e: use correct length for strncpy

Hi!

> From: Mitch Williams <mitch.a.williams@...el.com>
> 
> [ Upstream commit 7eb74ff891b4e94b8bac48f648a21e4b94ddee64 ]
> 
> Caught by GCC 8. When we provide a length for strncpy, we should not
> include the terminating null. So we must tell it one less than the size
> of the destination buffer.

> +++ b/drivers/net/ethernet/intel/i40e/i40e_ptp.c
> @@ -694,7 +694,8 @@ static long i40e_ptp_create_clock(struct i40e_pf *pf)
>  	if (!IS_ERR_OR_NULL(pf->ptp_clock))
>  		return 0;
>  
> -	strncpy(pf->ptp_caps.name, i40e_driver_name, sizeof(pf->ptp_caps.name));
> +	strncpy(pf->ptp_caps.name, i40e_driver_name,
> +		sizeof(pf->ptp_caps.name) - 1);
>  	pf->ptp_caps.owner = THIS_MODULE;
>  	pf->ptp_caps.max_adj = 999999999;
>  	pf->ptp_caps.n_ext_ts = 0;

So... pf is allocated with kzalloc, which will provide the null
termination... so the code is okay.

On the other hand, the = 0 below is unneeded by the same logic, so
this is a bit confusing.

Best regards,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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