From: Kees Cook <keescook@chromium.org>
To: Jakub Kicinski <kuba@kernel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
Subash Abhinov Kasiviswanathan <quic_subashab@quicinc.com>,
Sean Tranchetti <quic_stranche@quicinc.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] net: ethernet: rmnet: Replace zero-length array with DECLARE_FLEX_ARRAY() helper
Date: Mon, 26 Sep 2022 19:22:30 -0700 [thread overview]
Message-ID: <202209261920.3A2EA07D4@keescook> (raw)
In-Reply-To: <20220926172604.71a20b7d@kernel.org>
On Mon, Sep 26, 2022 at 05:26:04PM -0700, Jakub Kicinski wrote:
> On Mon, 26 Sep 2022 15:02:48 -0700 Kees Cook wrote:
> > On Mon, Sep 26, 2022 at 04:50:03PM -0500, Gustavo A. R. Silva wrote:
> > > Zero-length arrays are deprecated and we are moving towards adopting
> > > C99 flexible-array members, instead. So, replace zero-length arrays
> > > declarations in anonymous union with the new DECLARE_FLEX_ARRAY()
> > > helper macro.
> > >
> > > This helper allows for flexible-array members in unions.
> > >
> > > Link: https://github.com/KSPP/linux/issues/193
> > > Link: https://github.com/KSPP/linux/issues/221
> > > Link: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> >
> > Reviewed-by: Kees Cook <keescook@chromium.org>
>
> Not directly related to this patch, but I just had to look at pahole
> output for sk_buff and the struct_group() stuff makes is really painful
> to read :/ Offsets for the members are relative to the "group" and they
> are all repeated.
>
> Is there any chance you could fix that? Before we sprinkle more pixie
> dust around, perhaps?
Unfortunately I don't see a way around it until we can make changes to
the C language spec, and that's measured in decades. :(
Perhaps we could add some kind of heuristic to pahole to "hide" one of
the internal struct_group() copies, and to hide the empty flexible-array
wrapper structs? (pahole already can't tell the difference between a
0-length array and a flexible-array.) Would that be workable?
--
Kees Cook
next prev parent reply other threads:[~2022-09-27 2:22 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-26 21:50 [PATCH][next] net: ethernet: rmnet: Replace zero-length array with DECLARE_FLEX_ARRAY() helper Gustavo A. R. Silva
2022-09-26 22:02 ` Kees Cook
2022-09-27 0:26 ` Jakub Kicinski
2022-09-27 2:22 ` Kees Cook [this message]
2022-09-27 14:07 ` Jakub Kicinski
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