linux-hardening - Re: [PATCH][next] staging: greybus: i2c: Use struct_size() helper in gb_i2c_operation

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Date:   Mon, 24 Jan 2022 14:42:53 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Viresh Kumar <vireshk@...nel.org>, Johan Hovold <johan@...nel.org>,
        Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] staging: greybus: i2c: Use struct_size() helper in
 gb_i2c_operation_create()

On Mon, Jan 24, 2022 at 12:19:03PM -0800, Kees Cook wrote:
> On Fri, Jan 21, 2022 at 04:22:50PM -0600, Gustavo A. R. Silva wrote:
> > Make use of the struct_size() helper instead of an open-coded version,
> > in order to avoid any potential type mistakes or integer overflows that,
> > in the worst scenario, could lead to heap overflows.
> > 
> > Also, address the following sparse warnings:
> > drivers/staging/greybus/i2c.c:111:24: warning: using sizeof on a flexible structure
> > 
> > Link: https://github.com/KSPP/linux/issues/174
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> > ---
> >  drivers/staging/greybus/i2c.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/staging/greybus/i2c.c b/drivers/staging/greybus/i2c.c
> > index de2f6516da09..9dfc6791c20e 100644
> > --- a/drivers/staging/greybus/i2c.c
> > +++ b/drivers/staging/greybus/i2c.c
> > @@ -108,9 +108,7 @@ gb_i2c_operation_create(struct gb_connection *connection,
> >  		else
> >  			data_out_size += (u32)msg->len;
> >  
> > -	request_size = sizeof(*request);
> > -	request_size += msg_count * sizeof(*op);
> > -	request_size += data_out_size;
> > +	request_size = struct_size(request, ops, msg_count) + data_out_size;
> 
> This could still overflow if struct_size() returns SIZE_MAX. Perhaps:

uggh... I got too excited with all the new cases reported. 
> 
> 	if (check_add_overflow(struct_size(request, ops, msg_count),
> 			       data_out_size, &request_size))
> 		request_size = SIZE_MAX;

Yep; I'll respin and include this change, thanks!
> 
> I should brush off the saturating arithmetic helpers series:
> https://lore.kernel.org/all/20210920180853.1825195-1-keescook@chromium.org/

Yeah; those helpers are very much needed in many places we need to audit...

--
Gustavo