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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id q13sm218718pjq.10.2021.07.29.19.31.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jul 2021 19:31:09 -0700 (PDT) Date: Thu, 29 Jul 2021 19:31:08 -0700 From: Kees Cook To: Bart Van Assche Cc: linux-hardening@vger.kernel.org, "Gustavo A. R. Silva" , Keith Packard , Greg Kroah-Hartman , Andrew Morton , linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, netdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-staging@lists.linux.dev, linux-block@vger.kernel.org, linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH 48/64] drbd: Use struct_group() to zero algs Message-ID: <202107291845.1E1528D@keescook> References: <20210727205855.411487-1-keescook@chromium.org> <20210727205855.411487-49-keescook@chromium.org> <1cc74e5e-8d28-6da4-244e-861eac075ca2@acm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1cc74e5e-8d28-6da4-244e-861eac075ca2@acm.org> Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org On Wed, Jul 28, 2021 at 02:45:55PM -0700, Bart Van Assche wrote: > On 7/27/21 1:58 PM, Kees Cook wrote: > > In preparation for FORTIFY_SOURCE performing compile-time and run-time > > field bounds checking for memset(), avoid intentionally writing across > > neighboring fields. > > > > Add a struct_group() for the algs so that memset() can correctly reason > > about the size. > > > > Signed-off-by: Kees Cook > > --- > > drivers/block/drbd/drbd_main.c | 3 ++- > > drivers/block/drbd/drbd_protocol.h | 6 ++++-- > > drivers/block/drbd/drbd_receiver.c | 3 ++- > > 3 files changed, 8 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c > > index 55234a558e98..b824679cfcb2 100644 > > --- a/drivers/block/drbd/drbd_main.c > > +++ b/drivers/block/drbd/drbd_main.c > > @@ -729,7 +729,8 @@ int drbd_send_sync_param(struct drbd_peer_device *peer_device) > > cmd = apv >= 89 ? P_SYNC_PARAM89 : P_SYNC_PARAM; > > /* initialize verify_alg and csums_alg */ > > - memset(p->verify_alg, 0, 2 * SHARED_SECRET_MAX); > > + BUILD_BUG_ON(sizeof(p->algs) != 2 * SHARED_SECRET_MAX); > > + memset(&p->algs, 0, sizeof(p->algs)); > > if (get_ldev(peer_device->device)) { > > dc = rcu_dereference(peer_device->device->ldev->disk_conf); > > diff --git a/drivers/block/drbd/drbd_protocol.h b/drivers/block/drbd/drbd_protocol.h > > index dea59c92ecc1..a882b65ab5d2 100644 > > --- a/drivers/block/drbd/drbd_protocol.h > > +++ b/drivers/block/drbd/drbd_protocol.h > > @@ -283,8 +283,10 @@ struct p_rs_param_89 { > > struct p_rs_param_95 { > > u32 resync_rate; > > - char verify_alg[SHARED_SECRET_MAX]; > > - char csums_alg[SHARED_SECRET_MAX]; > > + struct_group(algs, > > + char verify_alg[SHARED_SECRET_MAX]; > > + char csums_alg[SHARED_SECRET_MAX]; > > + ); > > u32 c_plan_ahead; > > u32 c_delay_target; > > u32 c_fill_target; > > diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c > > index 1f740e42e457..6df2539e215b 100644 > > --- a/drivers/block/drbd/drbd_receiver.c > > +++ b/drivers/block/drbd/drbd_receiver.c > > @@ -3921,7 +3921,8 @@ static int receive_SyncParam(struct drbd_connection *connection, struct packet_i > > /* initialize verify_alg and csums_alg */ > > p = pi->data; > > - memset(p->verify_alg, 0, 2 * SHARED_SECRET_MAX); > > + BUILD_BUG_ON(sizeof(p->algs) != 2 * SHARED_SECRET_MAX); > > + memset(&p->algs, 0, sizeof(p->algs)); > > Using struct_group() introduces complexity. Has it been considered not to > modify struct p_rs_param_95 and instead to use two memset() calls instead of > one (one memset() call per member)? I went this direction because using two memset()s (or memcpy()s in other patches) changes the machine code. It's not much of a change, but it seems easier to justify "no binary changes" via the use of struct_group(). If splitting the memset() is preferred, I can totally do that instead. :) -Kees -- Kees Cook