linux-hardening - Re: [PATCH] RDMA/cxgb4: Replace 0-length arrays with flexible arrays

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Date:   Fri, 13 Jan 2023 17:03:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Potnuri Bharat Teja <bharat@...lsio.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] RDMA/cxgb4: Replace 0-length arrays with flexible arrays

On Sun, Jan 08, 2023 at 02:08:52PM +0200, Leon Romanovsky wrote:
> On Thu, Jan 05, 2023 at 02:32:32PM -0800, Kees Cook wrote:
> > Zero-length arrays are deprecated[1]. Replace all remaining
> > 0-length arrays with flexible arrays. Detected with GCC 13, using
> > -fstrict-flex-arrays=3:
> > 
> > In function 'build_rdma_write',
> >     inlined from 'c4iw_post_send' at ../drivers/infiniband/hw/cxgb4/qp.c:1173:10:
> > ../drivers/infiniband/hw/cxgb4/qp.c:597:38: warning: array subscript 0 is outside array bounds of 'struct fw_ri_immd[0]' [-Warray-bounds=]
> >   597 |                 wqe->write.u.immd_src[0].r2 = 0;
> >       |                 ~~~~~~~~~~~~~~~~~~~~~^~~
> > ../drivers/infiniband/hw/cxgb4/t4fw_ri_api.h: In function 'c4iw_post_send':
> > ../drivers/infiniband/hw/cxgb4/t4fw_ri_api.h:567:35: note: while referencing 'immd_src'
> >   567 |                 struct fw_ri_immd immd_src[0];
> >       |                                   ^~~~~~~~
> > 
> > Additionally drop the unused C99_NOT_SUPPORTED ifndef lines.
> > 
> > [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
> > 
> > Cc: Potnuri Bharat Teja <bharat@...lsio.com>
> > Cc: Jason Gunthorpe <jgg@...pe.ca>
> > Cc: Leon Romanovsky <leon@...nel.org>
> > Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> > Cc: linux-rdma@...r.kernel.org
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> >  drivers/infiniband/hw/cxgb4/t4fw_ri_api.h | 26 ++++++-----------------
> >  1 file changed, 6 insertions(+), 20 deletions(-)
> 
> <...>
> 
> >  #define FW_RI_SEND_WR_SENDOP_S		0
> > @@ -618,12 +606,10 @@ struct fw_ri_rdma_write_cmpl_wr {
> >  		struct fw_ri_isgl isgl_src;
> >  	} u_cmpl;
> >  	__be64 r3;
> > -#ifndef C99_NOT_SUPPORTED
> >  	union fw_ri_write {
> > -		struct fw_ri_immd immd_src[0];
> > -		struct fw_ri_isgl isgl_src[0];
> > +		DECLARE_FLEX_ARRAY(struct fw_ri_immd, immd_src);
> > +		DECLARE_FLEX_ARRAY(struct fw_ri_isgl, isgl_src);
> 
> smatch built from commit 40351132df3b ("strlen: add __builtin and
> __fortify functions") produces the following warning:
> drivers/infiniband/hw/cxgb4/t4fw_ri_api.h:575:17: warning: array of flexible structures
> 
> Is it expected? What will prevent from getting this warning from 0-day
> build bots?

Err, I'm not sure I understand? Does smatch define "C99_NOT_SUPPORTED"?

-- 
Kees Cook