From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2CCF935A385 for ; Sat, 18 Jul 2026 21:50:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784411432; cv=none; b=YyFzdkbuHaznZEIPEv10z0xyYZN7ubvTPIwaiCNhbMJm5ZP9qtgR6GkmKj++PaRFYUHP25cpaEZJUskjbIw1lewMlQAdPsaBK9oppBgGiN8iOM0coLC9go2XHRTUddAIj5990N3CfdP3DnKgq2IGhKmCGbN5kyaqrtFoIJSHtnA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784411432; c=relaxed/simple; bh=DQuyWTeYe/0KkPJN9R/6FONkM8H9RaDKoZruMYBRMIo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=FYTGlWqco8jd3COvSXkzko+vrZaOIBfSwCSREIHljxupsyKHwxZa8t535Dku3xbTP2nZty+4UfQwO/OBNlVX5wmlavId72kVE3Wx6pCY8gUQ1jGWp+tbwJxAm5iJoj0teUQ5EC8a056YTfAQPpB/BB9mOzmHGzU7MDSbkUcCD70= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fDW0UqE1; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fDW0UqE1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3086A1F00A3E; Sat, 18 Jul 2026 21:50:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784411430; bh=VKix8E37tK5ZbJz1cbQPVOiNQM8bE40Oj7iza5eQFto=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=fDW0UqE1MeRuWce98ZpU9kQv6gBwwUg2w0QLXx93vW3YFUIgGOUskuZwA/VXkVXNC K1R66PuL4CZmySTsGt/tf6LuwG17yi3GgbhAToHY65ALEi41TMvZ9/C81+53GukT2s VzyGVkxHBb1wpNKv8sRGqg9mxUFJhrB4bCnsK0ksQGEal3IC0Whqrk/ZpazULVQ80w q+AJ+29mMK0ID+F0fnX3aWBRnFTdVBh2UNSFoD4v0puqPWld71XhCCsgnM8Ovpk7SM Q9PKWlRuyQnkeQyPoX2JA4TAdjTL8vlvT4Eb1ABb0vyBjvDk9x9j61drTYMMrRJmh3 xwoymiBXF/XKg== From: Sasha Levin To: stable@vger.kernel.org Cc: Vlad Poenaru , Emil Tsalapatis , Alexei Starovoitov , Sasha Levin Subject: [PATCH 6.6.y 2/2] bpf: Allow LPM map access from sleepable BPF programs Date: Sat, 18 Jul 2026 17:50:27 -0400 Message-ID: <20260718215027.3447522-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260718215027.3447522-1-sashal@kernel.org> References: <2026071450-landmine-pouring-a4f5@gregkh> <20260718215027.3447522-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Vlad Poenaru [ Upstream commit 2f884d371fafea137afea504d49ee4a7c8d7985b ] 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(). trie_update_elem() and trie_delete_elem() have the same problem in a different form: they walk the trie with plain rcu_dereference(), which asserts rcu_read_lock_held() unconditionally. Both are reachable from sleepable BPF programs via the bpf_map_update_elem / bpf_map_delete_elem helpers, and from the syscall path under classic rcu_read_lock(). In the writer paths the trie is actually protected by trie->lock (an rqspinlock taken across the walk); we never relied on the RCU read-side lock to keep nodes alive there. A sleepable LSM hook that ends up touching an LPM trie therefore triggers lockdep on debug kernels: ============================= 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 touches an LPM trie, which is increasingly common. For the lookup path, switch the rcu_dereference_check() annotation from rcu_read_lock_bh_held() to bpf_rcu_lock_held(), which accepts all three contexts (classic, BH, Tasks Trace). Other map types already follow this convention. For trie_update_elem() and trie_delete_elem(), annotate the walks as rcu_dereference_protected(*p, 1) -- matching trie_free() in the same file -- since trie->lock is held across the walk. rqspinlock has no lockdep_map, so the predicate degenerates to '1' rather than lockdep_is_held(&trie->lock); the protection is real but not machine-verifiable. trie_get_next_key() also uses bare rcu_dereference() but is reachable only from the BPF syscall, which holds classic rcu_read_lock() before dispatching, so it is left untouched. Fixes: 694cea395fde ("bpf: Allow RCU-protected lookups to happen from bh context") Cc: stable@vger.kernel.org Signed-off-by: Vlad Poenaru Reviewed-by: Emil Tsalapatis Link: https://lore.kernel.org/r/20260609135558.193287-2-vlad.wing@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/lpm_trie.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c index 15c2525900fa31..62a9ce1969d090 100644 --- a/kernel/bpf/lpm_trie.c +++ b/kernel/bpf/lpm_trie.c @@ -237,7 +237,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key) /* Start walking the trie from the root node ... */ - for (node = rcu_dereference_check(trie->root, rcu_read_lock_bh_held()); + for (node = rcu_dereference_check(trie->root, bpf_rcu_lock_held()); node;) { unsigned int next_bit; size_t matchlen; @@ -271,7 +271,7 @@ static void *trie_lookup_elem(struct bpf_map *map, void *_key) */ next_bit = extract_bit(key->data, node->prefixlen); node = rcu_dereference_check(node->child[next_bit], - rcu_read_lock_bh_held()); + bpf_rcu_lock_held()); } if (!found) @@ -354,7 +354,7 @@ static long trie_update_elem(struct bpf_map *map, */ slot = &trie->root; - while ((node = rcu_dereference(*slot))) { + while ((node = rcu_dereference_protected(*slot, 1))) { matchlen = longest_prefix_match(trie, node, key); if (node->prefixlen != matchlen || @@ -475,7 +475,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key) trim = &trie->root; trim2 = trim; parent = NULL; - while ((node = rcu_dereference(*trim))) { + while ((node = rcu_dereference_protected(*trim, 1))) { matchlen = longest_prefix_match(trie, node, key); if (node->prefixlen != matchlen || -- 2.53.0