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Tue, 03 Nov 2026 08:55:56 -0800 (PST) Received: from andreayoga.wind3.hub ([31.189.68.219]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4abea533a1esm239726215e9.1.2026.11.03.08.55.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 08:55:55 -0800 (PST) From: Andrea Parri To: kpsingh@kernel.org, matt@bobrowski.net, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com Cc: Andrea Parri , martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, sdf@fomichev.me, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v2] bpf, lsm: Fix cgroup shim selection for socket hooks Date: Tue, 3 Nov 2026 17:55:40 +0100 Message-ID: <20261103165541.291744-1-parri.andrea@gmail.com> X-Mailer: git-send-email 2.53.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit bpf_lsm_find_cgroup_shim() picks the shim that runs a BPF_LSM_CGROUP program from the first argument of the attached hook. It compares args[0].type, the BTF id of the argument's pointer type, against btf_sock_ids[], which holds the struct ids of struct socket and struct sock. A pointer id is never equal to a struct id, so neither branch is taken and every cgroup LSM program runs through __cgroup_bpf_run_lsm_current(). Socket and sock hooks therefore run against task_dfl_cgroup(current) instead of the socket's cgroup. When a socket is used from a cgroup other than the one that created it, the caller's cgroup policy is applied instead of the socket's, and __cgroup_bpf_run_lsm_socket() and __cgroup_bpf_run_lsm_sock() are dead code. Resolve the argument's pointee with btf_type_resolve_ptr() and compare that id against btf_sock_ids[]. Two socket hooks are not always called with a usable socket: ip_cmsg_recv_security() passes a NULL socket to socket_getpeersec_dgram, and sock_create_lite() calls socket_post_create before sock->sk is set. Add both to bpf_lsm_current_hooks, so that their cgroup does not depend on the caller. socket_post_create is unchanged when called from __sock_create(), where the current task allocates the sk and gives it its cgroup. socket_getpeersec_dgram keeps the current cgroup, as today. The other socket hooks always get a socket with an sk, and the sock hooks a non-NULL sk. Existing BPF_LSM_CGROUP users will see a behavior change. The other socket and sock hooks now run the socket's cgroup programs, as described in commit 69fd337a975c ("bpf: per-cgroup lsm flavor"). Hooks that can run in softirq, such as socket_sock_rcv_skb, inet_conn_request and sk_getsecid, no longer depend on which task was interrupted. The bug was found with the help of an LLM. Suggested-by: Alexei Starovoitov Signed-off-by: Andrea Parri --- v2: - Add socket_post_create and socket_getpeersec_dgram to bpf_lsm_current_hooks instead of falling back to the current cgroup in __cgroup_bpf_run_lsm_socket() (Alexei) - Drop Fixes: and Cc: stable, target bpf-next (Alexei) v1: https://lore.kernel.org/bpf/20261102152913.366237-1-parri.andrea@gmail.com/ kernel/bpf/bpf_lsm.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c index f58dce888ff4a..485e8fe8524c8 100644 --- a/kernel/bpf/bpf_lsm.c +++ b/kernel/bpf/bpf_lsm.c @@ -66,6 +66,10 @@ BTF_SET_START(bpf_lsm_current_hooks) #ifdef CONFIG_SECURITY_NETWORK BTF_ID(func, bpf_lsm_sk_alloc_security) BTF_ID(func, bpf_lsm_sk_free_security) +/* sock->sk is NULL in sock_create_lite() */ +BTF_ID(func, bpf_lsm_socket_post_create) +/* sock is NULL in ip_cmsg_recv_security() */ +BTF_ID(func, bpf_lsm_socket_getpeersec_dgram) #endif BTF_SET_END(bpf_lsm_current_hooks) @@ -95,6 +99,7 @@ void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t *bpf_func) { const struct btf_param *args __maybe_unused; + u32 id __maybe_unused = 0; if (btf_type_vlen(prog->aux->attach_func_proto) < 1 || btf_id_set_contains(&bpf_lsm_current_hooks, @@ -105,10 +110,12 @@ void bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, #ifdef CONFIG_NET args = btf_params(prog->aux->attach_func_proto); + /* args[0].type is the id of the pointer. btf_sock_ids[] has structs. */ + btf_type_resolve_ptr(prog->aux->attach_btf, args[0].type, &id); - if (args[0].type == btf_sock_ids[BTF_SOCK_TYPE_SOCKET]) + if (id == btf_sock_ids[BTF_SOCK_TYPE_SOCKET]) *bpf_func = __cgroup_bpf_run_lsm_socket; - else if (args[0].type == btf_sock_ids[BTF_SOCK_TYPE_SOCK]) + else if (id == btf_sock_ids[BTF_SOCK_TYPE_SOCK]) *bpf_func = __cgroup_bpf_run_lsm_sock; else #endif -- 2.53.0