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Fri, 29 May 2026 10:42:44 -0700 (PDT) Received: from localhost ([2a03:2880:32ff:7::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4909c13d018sm25065735e9.8.2026.05.29.10.42.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 May 2026 10:42:41 -0700 (PDT) From: Vlad Poenaru To: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org Cc: Martin KaFai Lau , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH bpf] bpf, lpm_trie: Allow lookups from sleepable BPF programs Date: Fri, 29 May 2026 10:42:33 -0700 Message-ID: <20260529174233.2954240-1-vlad.wing@gmail.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" trie_lookup_elem() annotates its rcu_dereference_check() walks with only rcu_read_lock_bh_held(). Because rcu_dereference_check(p, c) resolves to "c || rcu_read_lock_held()", this passes for XDP/NAPI and classic RCU readers but fails for sleepable BPF programs, which enter via __bpf_prog_enter_sleepable() and hold only rcu_read_lock_trace(). A sleepable LSM hook that ends up doing bpf_map_lookup_elem() on an LPM trie therefore triggers lockdep on debug kernels: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D WARNING: suspicious RCU usage 7.1.0-... Tainted: G E ----------------------------- kernel/bpf/lpm_trie.c:249 suspicious rcu_dereference_check() usage! 1 lock held by net_tests/540: #0: (rcu_tasks_trace_srcu_struct){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x26/0x280 Call Trace: dump_stack_lvl lockdep_rcu_suspicious trie_lookup_elem bpf_prog_..._enforce_security_socket_connect bpf_trampoline_... security_socket_connect __sys_connect do_syscall_64 This is lockdep-only -- no UAF, since Tasks Trace RCU does serialize against the trie's reclaim path -- but it spams the console once per distinct callsite on every debug kernel running a sleepable BPF LSM that does map lookups on an LPM trie, which is increasingly common. Other map types already use the bpf_rcu_lock_held() helper, which accepts all three contexts (classic, BH, Tasks Trace). Use it here as well, matching the established convention. Fixes: 694cea395fde ("bpf: Allow RCU-protected lookups to happen from bh co= ntext") Cc: stable@vger.kernel.org Signed-off-by: Vlad Poenaru Reviewed-by: Emil Tsalapatis --- kernel/bpf/lpm_trie.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index 0f57608b385d..ac36063cb7e6 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -246,7 +246,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void= *_key) =20 /* Start walking the trie from the root node ... */ =20 - for (node =3D rcu_dereference_check(trie->root, rcu_read_lock_bh_held()); + for (node =3D rcu_dereference_check(trie->root, bpf_rcu_lock_held()); node;) { unsigned int next_bit; size_t matchlen; @@ -280,7 +280,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void= *_key) */ next_bit =3D extract_bit(key->data, node->prefixlen); node =3D rcu_dereference_check(node->child[next_bit], - rcu_read_lock_bh_held()); + bpf_rcu_lock_held()); } =20 if (!found) --=20 2.53.0-Meta