linux-hardening - Re: [PATCH v3 1/2] wifi: brcm80211: replace deprecated strncpy with strscpy

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Date: Thu, 26 Oct 2023 10:20:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Arend van Spriel <aspriel@...il.com>,
	Franky Lin <franky.lin@...adcom.com>,
	Hante Meuleman <hante.meuleman@...adcom.com>,
	Kalle Valo <kvalo@...nel.org>, linux-wireless@...r.kernel.org,
	brcm80211-dev-list.pdl@...adcom.com,
	SHA-cyfmac-dev-list@...ineon.com, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 1/2] wifi: brcm80211: replace deprecated strncpy with
 strscpy

On Tue, Oct 17, 2023 at 08:11:28PM +0000, Justin Stitt wrote:
> Let's move away from using strncpy and instead favor a less ambiguous
> and more robust interface.
> 
> For ifp->ndev->name, we expect ifp->ndev->name to be NUL-terminated based
> on its use in format strings within core.c:
> 67 |       char *brcmf_ifname(struct brcmf_if *ifp)
> 68 |       {
> 69 |            if (!ifp)
> 70 |                    return "<if_null>";
> 71 |
> 72 |            if (ifp->ndev)
> 73 |                    return ifp->ndev->name;
> 74 |
> 75 |            return "<if_none>";
> 76 |       }
> ...
> 288 |       static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
> 289 |                                              struct net_device *ndev) {
> ...
> 330 |       brcmf_dbg(INFO, "%s: insufficient headroom (%d)\n",
> 331 |                 brcmf_ifname(ifp), head_delta);
> ...
> 336 |       bphy_err(drvr, "%s: failed to expand headroom\n",
> 337 |                brcmf_ifname(ifp));
> 
> For di->name, we expect di->name to be NUL-terminated based on its usage
> with format strings:
> |       brcms_dbg_dma(di->core,
> |                     "%s: DMA64 tx doesn't have AE set\n",
> |                     di->name);
> 
> Looking at its allocation we can see that it is already zero-allocated
> which means NUL-padding is not required:
> |       di = kzalloc(sizeof(struct dma_info), GFP_ATOMIC);
> 
> For wlc->modulecb[i].name, we expect each name in wlc->modulecb to be
> NUL-terminated based on their usage with strcmp():
> |       if (!strcmp(wlc->modulecb[i].name, name) &&
> 
> NUL-padding is not required as wlc is zero-allocated in:
> brcms_c_attach_malloc() ->
> |       wlc = kzalloc(sizeof(struct brcms_c_info), GFP_ATOMIC);
> 
> For all these cases, a suitable replacement is `strscpy` due to the fact
> that it guarantees NUL-termination on the destination buffer without
> unnecessarily NUL-padding.
> 
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Good; this looks like standard direct replacements.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook