From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yx1-f53.google.com (mail-yx1-f53.google.com [74.125.224.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6056B3E168C for ; Thu, 27 Aug 2026 23:55:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.224.53 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787874921; cv=none; b=fgXt9oSJXgJRwsIk9az7dmXF6Z7Qx55Kf38UsIPvLk6+X6oXyQXKG0+h0jCnY1G3rtS2DwmoZLL7yCCqyg9XIjn4Jv8pqNm1DxRXZ7TpIM/6ACNwm5WQRkGggoJLY0YX1f+HyBQc/k5lQ2BIgJ7d6/ZC3UAUNKsAKxI7O8Bm9s4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787874921; c=relaxed/simple; bh=17DL7rhafk1dsgIeYoK4mS2o50WhRjWyO2dEKqAEpdI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PXXYsGUrN05EjPWZrTqAhPUmdDAZ2ogF6uJrSkcnb7mUL04sBQsauCuUICme4glTrxkutTiqZ3UghAUI6v+CkUsszkIlGYKjLnhQHpnipqdKxAjRg1srXOGPHLrHi9uNzaTFAvPx1ZeaKhjfuojZOUGEtrb3p4x7lJwx8ZczxJE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=sC3pQT9w; arc=none smtp.client-ip=74.125.224.53 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="sC3pQT9w" Received: by mail-yx1-f53.google.com with SMTP id 956f58d0204a3-66d25d77713so481610d50.1 for ; Thu, 27 Aug 2026 16:55:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1787874916; x=1788479716; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=jvm7J3YSk1/1T92COXCSTc907ZSd3vJ2D2ODqJKXqh8=; b=sC3pQT9w16X8e1FpEkMG6skdnkz3y6W25eGE49xth0hbRGOZG8r9cJy7vO7hb7XVh1 HccgqlnWExlRcyHVA8kceftioB0FQVFphc9IDS195xgzYP6AdHXVkUfpGbWT2yqo1urv 6HBqjCNaTGuSz77ZNtDQGSOx6fyE/fMRl+6uU/D8huih79l4QcFg46gXATGclQf62NgP Y2ZJf4iXR9gBQ/jYy3yLN29KXKpBGaB6z/tjF57XDBRTtCpIQ85QvGI7s0HbQaTlcqIJ Iaqie7fqQL88FJFqsTiUDmu9ACHXSAxX8NijAIw/70hC2TxHMVlarBQ0yCN/sbVC9wsD QKWQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787874916; x=1788479716; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=jvm7J3YSk1/1T92COXCSTc907ZSd3vJ2D2ODqJKXqh8=; b=PWGmuz/G5No+Q8rpifjttSDldfkIcza+pcoe6VgMqWT9HkZXpLYPfDS3Ewb22TZ5jO Mro8en0ji+rq7R8yeNeAjiOO2Eve2OuVNiJ34i8T2t3XvrkhddKQNxOd23siAeE6Gcyh Fvoc+6Ef3Th7Crd2fhmeFHtNVGHW1dwAJjInAL2cJaJ3AoCq5+/1mX8K/ndIaCPFkfRz dsIGSwlVR/KGzGtFZBNt3L9oYTqrUO37Ugk5lhBot+tldy19ymWFK3J/iwbfsODRdbSK J53j2VeLTclBs9R8FC8JYhjvhcTDAlyLMg2gotcidEQI/k4hGdBX5GO6bPS8LEYKEYui 0ffQ== X-Forwarded-Encrypted: i=1; AHgh+Ro32LKQYYEpRgGOO8UB/d+Wu05O5qw6HtCnlvxhBdnHPhVuGo4T0et5NtAzQahgwuvdsNPIrEI=@vger.kernel.org X-Gm-Message-State: AFuF++mlNECjqAkwd3G+dKfPJQ+XO/2kuKQP5CWZl55BxM5KLVfyWFEQ ri+ewu/v1eNgaZZmKblEziy7yMzE1pk4cgg33J2IRDmvIfW0OYtTolz5 X-Gm-Gg: AR+sD12pVb8Hz92/KCOMx4LLFZutRdZrpeYPgBMG7nEN8LyXlqUlTnph3v6jB6vK4PR tsLjayHp68FInxzdA0himsCpQ2wRmoqodK9a2viJgkfLiYMKE2k21F2OOBdGMrLVbSyw+xSJUk3 VJpOA5ju4g5kNpun4aUmh8XzGGOYl5pT4tP9eoRGrwG+2mm3CdSGGUly5vnuktxJscvOCHtpQg1 zImiEUOvKWCUm40e5NoJ+wZT3LSa/qXKAmQ8CnzIxYl/27nU2kBFpYRiCVEb3rGvoXlGb9G0CMK f3kS3rkLVg7bB3cr6sGYjQ2WHTiWfmUkfeKMnGzM54Xq5xaeDg54K4TFwBujDdb0wAMJsuYBkKR KVbkXgOGeH8gBWlxGPl7S04oG9gpY4K46Bhu0cOaZ6O2KUdHwBouw9/Dti06VSEbC0/m2Po1/nd 2Y3s86ZUdcDmAIKhLOVuhwUYPZ1gp2m0KzdwrRGxoj6Ypx2IhswlvP4ZT31r8x3QtIZ2aVzdaU+ ZLCJQ== X-Received: by 2002:a53:b812:0:b0:66d:2b87:67d2 with SMTP id 956f58d0204a3-66e4c6505demr643968d50.14.1787874914413; Thu, 27 Aug 2026 16:55:14 -0700 (PDT) Received: from mac.lan ([136.55.173.105]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-66e4eb3dcdbsm55704d50.4.2026.08.27.16.55.13 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 27 Aug 2026 16:55:14 -0700 (PDT) From: "Cen Zhang (Microsoft)" To: edumazet@google.com, ncardwell@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com Cc: kuniyu@google.com, horms@kernel.org, matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org, yhs@fb.com, kafai@fb.com, andriin@fb.com, ast@kernel.org, netdev@vger.kernel.org, mptcp@lists.linux.dev, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, xmei5@asu.edu, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com, stable@vger.kernel.org Subject: [PATCH net v3 1/2] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION) Date: Thu, 27 Aug 2026 19:55:10 -0400 Message-ID: X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Cen Zhang (Microsoft Security FORGE Labs)" do_tcp_getsockopt() reads icsk->icsk_ca_ops->name without holding rcu_read_lock(). Since commit 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf"), icsk_ca_ops can point to dynamically allocated BPF struct_ops memory that may be freed concurrently via setsockopt(TCP_CONGESTION), leading to a use-after-free. BUG: KASAN: slab-use-after-free in _copy_to_user+0x37/0x60 Read of size 16 at addr ffff888013505260 by task exploit/149 _copy_to_user+0x37/0x60 do_tcp_getsockopt+0x158a/0x2460 (net/ipv4/tcp.c:4585) tcp_getsockopt+0x91/0xf0 __sys_getsockopt+0xf7/0x170 Fix this by holding rcu_read_lock() around the ca_ops->name access, using READ_ONCE() to load icsk_ca_ops, and copying the name to a stack buffer before releasing the lock. Also annotate the relevant icsk_ca_ops stores with WRITE_ONCE() to fix the accompanying KCSAN data-race issue. Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf") Suggested-by: Eric Dumazet Reported-by: Xiang Mei (Microsoft) Link: https://lore.kernel.org/all/20260821182449.79785-2-blbllhy@gmail.com/ Cc: AutonomousCodeSecurity@microsoft.com Cc: stable@vger.kernel.org Assisted-by: GitHub-Copilot:claude-opus-4.6 Reviewed-by: Eric Dumazet Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) --- Note: The adjacent TCP_ULP case has a similar read pattern on icsk_ulp_ops->name, but icsk_ulp_ops always points to static module data (no BPF struct_ops equivalent), so it is not affected. Changes in v3: - Fix the build failure by loading icsk_ca_ops inline. - Drop the unrelated WRITE_ONCE() conversion in mptcp_ca_reset(). Changes in v2: - Add READ_ONCE() for the icsk_ca_ops load. - Add WRITE_ONCE() for every explicit icsk_ca_ops store. --- net/ipv4/tcp.c | 14 +++++++++++--- net/ipv4/tcp_cong.c | 4 ++-- net/ipv4/tcp_dctcp.c | 2 +- net/ipv4/tcp_minisocks.c | 2 +- net/ipv4/tcp_output.c | 2 +- 5 files changed, 16 insertions(+), 8 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 455441f1b..55ca74f60 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -4576,16 +4576,24 @@ int do_tcp_getsockopt(struct sock *sk, int level, val = !inet_csk_in_pingpong_mode(sk); break; - case TCP_CONGESTION: + case TCP_CONGESTION: { + char ca_name[TCP_CA_NAME_MAX] = {}; + if (copy_from_sockptr(&len, optlen, sizeof(int))) return -EFAULT; len = min_t(unsigned int, len, TCP_CA_NAME_MAX); if (copy_to_sockptr(optlen, &len, sizeof(int))) return -EFAULT; - if (copy_to_sockptr(optval, icsk->icsk_ca_ops->name, len)) + + rcu_read_lock(); + memcpy(ca_name, READ_ONCE(icsk->icsk_ca_ops)->name, + sizeof(ca_name)); + rcu_read_unlock(); + + if (copy_to_sockptr(optval, ca_name, len)) return -EFAULT; return 0; - + } case TCP_ULP: if (copy_from_sockptr(&len, optlen, sizeof(int))) return -EFAULT; diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index e9f6c77e0..8e83ef81f 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -223,7 +223,7 @@ void tcp_assign_congestion_control(struct sock *sk) ca = rcu_dereference(net->ipv4.tcp_congestion_control); if (unlikely(!bpf_try_module_get(ca, ca->owner))) ca = &tcp_reno; - icsk->icsk_ca_ops = ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); rcu_read_unlock(); memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv)); @@ -253,7 +253,7 @@ static void tcp_reinit_congestion_control(struct sock *sk, struct inet_connection_sock *icsk = inet_csk(sk); tcp_cleanup_congestion_control(sk); - icsk->icsk_ca_ops = ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); icsk->icsk_ca_setsockopt = 1; memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv)); diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c index 274e628e7..99f68c299 100644 --- a/net/ipv4/tcp_dctcp.c +++ b/net/ipv4/tcp_dctcp.c @@ -111,7 +111,7 @@ __bpf_kfunc static void dctcp_init(struct sock *sk) /* No ECN support? Fall back to Reno. Also need to clear * ECT from sk since it is set during 3WHS for DCTCP. */ - inet_csk(sk)->icsk_ca_ops = &dctcp_reno; + WRITE_ONCE(inet_csk(sk)->icsk_ca_ops, &dctcp_reno); INET_ECN_dontxmit(sk); } diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index 6ab3e3a0b..def3b25ab 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -507,7 +507,7 @@ void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) ca = tcp_ca_find_key(ca_key); if (likely(ca && bpf_try_module_get(ca, ca->owner))) { icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); - icsk->icsk_ca_ops = ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); ca_got_dst = true; } rcu_read_unlock(); diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index d7c1444b5..e72ebfe7b 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -4092,7 +4092,7 @@ static void tcp_ca_dst_init(struct sock *sk, const struct dst_entry *dst) if (likely(ca && bpf_try_module_get(ca, ca->owner))) { bpf_module_put(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner); icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); - icsk->icsk_ca_ops = ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); } rcu_read_unlock(); } -- 2.43.0