From: Erick Archer <erick.archer@outlook.com>
To: Kees Cook <keescook@chromium.org>
Cc: Erick Archer <erick.archer@outlook.com>,
Marek Lindner <mareklindner@neomailbox.ch>,
Simon Wunderlich <sw@simonwunderlich.de>,
Antonio Quartulli <a@unstable.cc>,
Sven Eckelmann <sven@narfation.org>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
b.a.t.m.a.n@lists.open-mesh.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, linux-hardening@vger.kernel.org,
llvm@lists.linux.dev
Subject: Re: [PATCH v2] batman-adv: Add flex array to struct batadv_tvlv_tt_data
Date: Wed, 1 May 2024 15:35:57 +0200 [thread overview]
Message-ID: <AS8PR02MB7237099D421106BC1EF10BDB8B192@AS8PR02MB7237.eurprd02.prod.outlook.com> (raw)
In-Reply-To: <202404291030.F760C26@keescook>
Hi Kees,
On Mon, Apr 29, 2024 at 10:36:23AM -0700, Kees Cook wrote:
> On Fri, Apr 26, 2024 at 07:22:47PM +0200, Erick Archer wrote:
> >
> > @@ -3957,17 +3947,18 @@ static void batadv_tt_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
> >
> > num_vlan = ntohs(tt_data->num_vlan);
> >
> > - if (tvlv_value_len < sizeof(*tt_vlan) * num_vlan)
> > + flex_size = flex_array_size(tt_data, vlan_data, num_vlan);
> > + if (tvlv_value_len < flex_size)
> > return;
> >
> > - tt_vlan = (struct batadv_tvlv_tt_vlan_data *)(tt_data + 1);
> > - tt_change = (struct batadv_tvlv_tt_change *)(tt_vlan + num_vlan);
> > - tvlv_value_len -= sizeof(*tt_vlan) * num_vlan;
> > + tt_change = (struct batadv_tvlv_tt_change *)(tt_data->vlan_data +
> > + num_vlan);
>
> This is the only part I'm a little worried about. The math all checks
> out, but the compiler may get bothered about performing a pointer
> calculation using the vlan_data flexible array memory. As in, this may
> be calculated as an array offset, since it is the same as:
>
> &tt_data->vlan_data[num_vlan]
>
> Which, for big endian where __counted_by is in effect, the bounds
> checker may throw a fit since we're going past the end of the array. In
> other "multiple trailing flexible array" situations, we've done the
> addressing from the base pointer, since the compiler either knows the
> full allocation size or it knows nothing about it (this case, since it
> came from a "void *" function argument). I would suggest:
>
> tt_change = (struct batadv_tvlv_tt_change *)((void *)tt_data + flex_size);
>
First of all thanks for the review and the great explanation. The change
looks reasonable to me. I will send a new version with this suggestion.
Regards,
Erick
prev parent reply other threads:[~2024-05-01 14:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 17:22 [PATCH v2] batman-adv: Add flex array to struct batadv_tvlv_tt_data Erick Archer
2024-04-29 17:36 ` Kees Cook
2024-05-01 13:35 ` Erick Archer [this message]
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