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([2601:647:4000:d7:3f66:df55:a341:f79d]) by smtp.gmail.com with ESMTPSA id c15sm221003pfl.181.2021.07.29.19.57.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jul 2021 19:57:49 -0700 (PDT) Subject: Re: [PATCH 48/64] drbd: Use struct_group() to zero algs To: Kees Cook 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, Lars Ellenberg References: <20210727205855.411487-1-keescook@chromium.org> <20210727205855.411487-49-keescook@chromium.org> <1cc74e5e-8d28-6da4-244e-861eac075ca2@acm.org> <202107291845.1E1528D@keescook> From: Bart Van Assche Message-ID: <0d71917d-967f-beaa-d83e-a60fa254627c@acm.org> Date: Thu, 29 Jul 2021 19:57:47 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <202107291845.1E1528D@keescook> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/29/21 7:31 PM, Kees Cook wrote: > 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. > :) I don't have a strong opinion about this. Lars, do you want to comment on this patch? Thanks, Bart.