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[93.72.109.136]) by smtp.gmail.com with ESMTPSA id qb18-20020a1709077e9200b009adc5802d08sm8191805ejc.190.2023.09.20.03.49.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Sep 2023 03:49:03 -0700 (PDT) Message-ID: <5146e687-f5b8-86b2-e4e3-29871fe4fa5c@blackwall.org> Date: Wed, 20 Sep 2023 13:49:01 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 Subject: Re: [PATCH net-next v4 3/6] net: bridge: Track and limit dynamically learned FDB entries Content-Language: en-US To: Johannes Nixdorf , "David S. Miller" , Andrew Lunn , David Ahern , Eric Dumazet , Florian Fainelli , Ido Schimmel , Jakub Kicinski , Oleksij Rempel , Paolo Abeni , Roopa Prabhu , Shuah Khan , Vladimir Oltean Cc: bridge@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20230919-fdb_limit-v4-0-39f0293807b8@avm.de> <20230919-fdb_limit-v4-3-39f0293807b8@avm.de> From: Nikolay Aleksandrov In-Reply-To: <20230919-fdb_limit-v4-3-39f0293807b8@avm.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/19/23 11:12, Johannes Nixdorf wrote: > A malicious actor behind one bridge port may spam the kernel with packets > with a random source MAC address, each of which will create an FDB entry, > each of which is a dynamic allocation in the kernel. > > There are roughly 2^48 different MAC addresses, further limited by the > rhashtable they are stored in to 2^31. Each entry is of the type struct > net_bridge_fdb_entry, which is currently 128 bytes big. This means the > maximum amount of memory allocated for FDB entries is 2^31 * 128B = > 256GiB, which is too much for most computers. > > Mitigate this by maintaining a per bridge count of those automatically > generated entries in fdb_n_learned, and a limit in fdb_max_learned. If > the limit is hit new entries are not learned anymore. > > For backwards compatibility the default setting of 0 disables the limit. > > User-added entries by netlink or from bridge or bridge port addresses > are never blocked and do not count towards that limit. > > Introduce a new fdb entry flag BR_FDB_DYNAMIC_LEARNED to keep track of > whether an FDB entry is included in the count. The flag is enabled for > dynamically learned entries, and disabled for all other entries. This > should be equivalent to BR_FDB_ADDED_BY_USER and BR_FDB_LOCAL being unset, > but contrary to the two flags it can be toggled atomically. > > Atomicity is required here, as there are multiple callers that modify the > flags, but are not under a common lock (br_fdb_update is the exception > for br->hash_lock, br_fdb_external_learn_add for RTNL). > > Signed-off-by: Johannes Nixdorf > --- > net/bridge/br_fdb.c | 35 +++++++++++++++++++++++++++++++++-- > net/bridge/br_private.h | 4 ++++ > 2 files changed, 37 insertions(+), 2 deletions(-) > I think this is a good counting start. :) It'd be nice to get more eyes on this one. Acked-by: Nikolay Aleksandrov