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[2001:8b0:7a5a:26ff:60d6:619e:3324:40dc]) by smtp.gmail.com with ESMTPSA id 3sm4204565wms.36.2020.08.19.02.37.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Aug 2020 02:37:49 -0700 (PDT) From: Lorenz Bauer To: jakub@cloudflare.com, john.fastabend@gmail.com, Alexei Starovoitov , Daniel Borkmann Cc: kernel-team@cloudflare.com, Lorenz Bauer , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next 4/6] bpf: override the meaning of ARG_PTR_TO_MAP_VALUE for sockmap and sockhash Date: Wed, 19 Aug 2020 10:24:34 +0100 Message-Id: <20200819092436.58232-5-lmb@cloudflare.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200819092436.58232-1-lmb@cloudflare.com> References: <20200819092436.58232-1-lmb@cloudflare.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The verifier assumes that map values are simple blobs of memory, and therefore treats ARG_PTR_TO_MAP_VALUE, etc. as such. However, there are map types where this isn't true. For example, sockmap and sockhash store sockets. In general this isn't a big problem: we can just write helpers that explicitly requests PTR_TO_SOCKET instead of ARG_PTR_TO_MAP_VALUE. The one exception are the standard map helpers like map_update_elem, map_lookup_elem, etc. Here it would be nice we could overload the function prototype for different kinds of maps. Unfortunately, this isn't entirely straight forward: We only know the type of the map once we have resolved meta->map_ptr in check_func_arg. This means we can't swap out the prototype in check_helper_call until we're half way through the function. Instead, modify check_func_arg to treat ARG_PTR_TO_MAP_VALUE* to mean "the native type for the map" instead of "pointer to memory" for sockmap and sockhash. This means we don't have to modify the function prototype at all Signed-off-by: Lorenz Bauer --- kernel/bpf/verifier.c | 40 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b6ccfce3bf4c..47f9b94bb9d4 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3872,6 +3872,38 @@ static int int_ptr_type_to_size(enum bpf_arg_type type) return -EINVAL; } +static int override_map_arg_type(struct bpf_verifier_env *env, + const struct bpf_call_arg_meta *meta, + enum bpf_arg_type *arg_type) +{ + if (!meta->map_ptr) { + /* kernel subsystem misconfigured verifier */ + verbose(env, "invalid map_ptr to access map->type\n"); + return -EACCES; + } + + switch (meta->map_ptr->map_type) { + case BPF_MAP_TYPE_SOCKMAP: + case BPF_MAP_TYPE_SOCKHASH: + switch (*arg_type) { + case ARG_PTR_TO_MAP_VALUE: + *arg_type = ARG_PTR_TO_SOCKET; + break; + case ARG_PTR_TO_MAP_VALUE_OR_NULL: + *arg_type = ARG_PTR_TO_SOCKET_OR_NULL; + break; + default: + verbose(env, "invalid arg_type for sockmap/sockhash\n"); + return -EINVAL; + } + break; + + default: + break; + } + return 0; +} + static int check_func_arg(struct bpf_verifier_env *env, u32 arg, struct bpf_call_arg_meta *meta, const struct bpf_func_proto *fn) @@ -3904,6 +3936,14 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, return -EACCES; } + if (arg_type == ARG_PTR_TO_MAP_VALUE || + arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE || + arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) { + err = override_map_arg_type(env, meta, &arg_type); + if (err) + return err; + } + if (arg_type == ARG_PTR_TO_MAP_KEY || arg_type == ARG_PTR_TO_MAP_VALUE || arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE || -- 2.25.1