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Date:   Mon, 9 Oct 2023 13:42:12 -0700
From:   Kees Cook <keescook@chromium.org>
To:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Kalle Valo <kvalo@kernel.org>, linux-wireless@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] hostap: Add __counted_by for struct
 prism2_download_data and use struct_size()
Message-ID: <202310091341.74A2D82BB@keescook>
References: <ZSRXXvWMMkm7qqRW@work>
 <202310091253.665A9C9@keescook>
 <169f782e-9cc4-49bc-9618-ca6acc526e37@embeddedor.com>
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On Mon, Oct 09, 2023 at 02:33:01PM -0600, Gustavo A. R. Silva wrote:
> 
> 
> On 10/9/23 21:54, Kees Cook wrote:
> > On Mon, Oct 09, 2023 at 01:41:18PM -0600, Gustavo A. R. Silva wrote:
> > > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > > attribute. Flexible array members annotated with __counted_by can have
> > > their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> > > array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > > functions).
> > > 
> > > While there, use struct_size() helper, instead of the open-coded
> > > version, to calculate the size for the allocation of the whole
> > > flexible structure, including of course, the flexible-array member.
> > > 
> > > This code was found with the help of Coccinelle, and audited and
> > > fixed manually.
> > > 
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > > ---
> > >   drivers/net/wireless/intersil/hostap/hostap_download.c | 3 +--
> > >   drivers/net/wireless/intersil/hostap/hostap_wlan.h     | 2 +-
> > >   2 files changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/net/wireless/intersil/hostap/hostap_download.c b/drivers/net/wireless/intersil/hostap/hostap_download.c
> > > index 3672291ced5c..5e5bada28b5b 100644
> > > --- a/drivers/net/wireless/intersil/hostap/hostap_download.c
> > > +++ b/drivers/net/wireless/intersil/hostap/hostap_download.c
> > > @@ -732,8 +732,7 @@ static int prism2_download(local_info_t *local,
> > >   		goto out;
> > >   	}
> > > -	dl = kzalloc(sizeof(*dl) + param->num_areas *
> > > -		     sizeof(struct prism2_download_data_area), GFP_KERNEL);
> > > +	dl = kzalloc(struct_size(dl, data, param->num_areas), GFP_KERNEL);
> > >   	if (dl == NULL) {
> > >   		ret = -ENOMEM;
> > >   		goto out;
> > > diff --git a/drivers/net/wireless/intersil/hostap/hostap_wlan.h b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> > > index c25cd21d18bd..f71c0545c0be 100644
> > > --- a/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> > > +++ b/drivers/net/wireless/intersil/hostap/hostap_wlan.h
> > > @@ -617,7 +617,7 @@ struct prism2_download_data {
> > >   		u32 addr; /* wlan card address */
> > >   		u32 len;
> > >   		u8 *data; /* allocated data */
> > > -	} data[];
> > > +	} data[] __counted_by(num_areas);
> > >   };
> > 
> > Should this be considered a v2 of:
> > https://lore.kernel.org/linux-hardening/94848cc3-6f5c-46d7-8cc7-98a4f10865b3@embeddedor.com/
> > 
> > ?
> 
> Oops... sorry, I forgot I had reviewed this patch of yours.
> 
> > 
> > Yours is more complete since it includes the struct_size() change...
> > 
> 
> Should I resend this explicitly marking it as a v2?

I defer to Kalle -- your Subject is more accurate, so perhaps let's just
let this stand?

-- 
Kees Cook