linux-kernel - Re: [PATCH] staging/rtl8192u: Remove all strcpy() uses in favor of strscpy()

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Date:   Fri, 23 Jul 2021 20:16:25 +0200
From:   Len Baker <len.baker@....com>
To:     David Laight <David.Laight@...LAB.COM>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Len Baker <len.baker@....com>, Lee Jones <lee.jones@...aro.org>,
        Romain Perier <romain.perier@...il.com>,
        Allen Pais <apais@...ux.microsoft.com>,
        Dmitrii Wolf <dev.dragon@...ru>,
        Iain Craig <coldcity@...il.com>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging/rtl8192u: Remove all strcpy() uses in favor of
 strscpy()

Hi,

On Mon, Jul 19, 2021 at 08:49:54AM +0000, David Laight wrote:
> From: Len Baker
> > Sent: 18 July 2021 12:32
> >
> > strcpy() performs no bounds checking on the destination buffer. This
> > could result in linear overflows beyond the end of the buffer, leading
> > to all kinds of misbehaviors. The safe replacement is strscpy().
> >
> > Signed-off-by: Len Baker <len.baker@....com>
> > ---
> >  drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
> > b/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
> > index ab885353f668..1a193f900779 100644
> > --- a/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
> > +++ b/drivers/staging/rtl8192u/ieee80211/ieee80211_softmac.c
> > @@ -2226,7 +2226,8 @@ static void ieee80211_start_ibss_wq(struct work_struct *work)
> >  	mutex_lock(&ieee->wx_mutex);
> >
> >  	if (ieee->current_network.ssid_len == 0) {
> > -		strcpy(ieee->current_network.ssid, IEEE80211_DEFAULT_TX_ESSID);
> > +		strscpy(ieee->current_network.ssid, IEEE80211_DEFAULT_TX_ESSID,
> > +			sizeof(ieee->current_network.ssid));
>
> I'm pretty sure that recent compiler releases know enough
> about strcpy() to error overflows for strcpy() from quoted
> strings into char[].
>
> If these checks are enabled for kernel builds then they are
> actually safer than the run-time check above
> (which can be mistyped).
>
> The compiler can (it may not) convert the strcpy() into a memcpy()
> using the compile-time length of the quoted string.

I agree, but if we want to remove this function entirely from the kernel [1]
we need to replace all the strcpy() uses as a previous step. And the safe
replacement is strscpy() [2].

[1] https://github.com/KSPP/linux/issues/88
[2] https://www.kernel.org/doc/html/latest/process/deprecated.html#strcpy

> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

Thanks for the feedback,
Len