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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: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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) Reviewed-by: Breno Leitao Reviewed-by: Jiayuan Chen Reviewed-by: Matthieu Baerts (NGI0) --- 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 =3D !inet_csk_in_pingpong_mode(sk); break; =20 - case TCP_CONGESTION: + case TCP_CONGESTION: { + char ca_name[TCP_CA_NAME_MAX] =3D {}; + if (copy_from_sockptr(&len, optlen, sizeof(int))) return -EFAULT; len =3D 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 =3D rcu_dereference(net->ipv4.tcp_congestion_control); if (unlikely(!bpf_try_module_get(ca, ca->owner))) ca =3D &tcp_reno; - icsk->icsk_ca_ops =3D ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); rcu_read_unlock(); =20 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 =3D inet_csk(sk); =20 tcp_cleanup_congestion_control(sk); - icsk->icsk_ca_ops =3D ca; + WRITE_ONCE(icsk->icsk_ca_ops, ca); icsk->icsk_ca_setsockopt =3D 1; memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv)); =20 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. 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Thu, 27 Aug 2026 16:55:15 -0700 (PDT) Received: from mac.lan ([136.55.173.105]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-66e4eb3dcdbsm55704d50.4.2026.08.27.16.55.15 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 27 Aug 2026 16:55:15 -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 2/2] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CC_INFO) Date: Thu, 27 Aug 2026 19:55:11 -0400 Message-ID: <65fd3816ed5d541d9edd4bf4fcf97104a2cf907a.1787870710.git.blbllhy@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Cen Zhang (Microsoft Security FORGE Labs)" do_tcp_getsockopt() reads icsk->icsk_ca_ops and dereferences the get_info function pointer without rcu_read_lock(). With BPF struct_ops congestion control, ca_ops can point to dynamically allocated memory that is freed concurrently, resulting in a use-after-free when the kernel dereferences or calls through the stale pointer. BUG: KASAN: slab-use-after-free in do_tcp_getsockopt+0x2037/0x23e0 Read of size 8 at addr ffff888013701258 by task exploit/149 do_tcp_getsockopt+0x2037/0x23e0 (net/ipv4/tcp.c:4564) tcp_getsockopt+0x91/0xf0 __sys_getsockopt+0xf7/0x170 Fix this by wrapping the ca_ops load and get_info call within rcu_read_lock()/rcu_read_unlock(), and using READ_ONCE() to load the icsk_ca_ops pointer. Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf") Suggested-by: Eric Dumazet 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) Reviewed-by: Jiayuan Chen Reviewed-by: Matthieu Baerts (NGI0) --- Link: https://lore.kernel.org/all/20260821182449.79785-3-blbllhy@gmail.com/= (v1) Link: https://lore.kernel.org/all/20260826171344.4133-3-blbllhy@gmail.com/ = (v2) Changes in v3: - Annotate dctcp_get_info()'s icsk_ca_ops comparison with READ_ONCE(). Changes in v2: - Add READ_ONCE() for the icsk_ca_ops load. --- net/ipv4/tcp.c | 4 +++- net/ipv4/tcp_dctcp.c | 2 +- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 55ca74f60..71d4c5e6b 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -4561,9 +4561,11 @@ int do_tcp_getsockopt(struct sock *sk, int level, if (copy_from_sockptr(&len, optlen, sizeof(int))) return -EFAULT; =20 - ca_ops =3D icsk->icsk_ca_ops; + rcu_read_lock(); + ca_ops =3D READ_ONCE(icsk->icsk_ca_ops); if (ca_ops && ca_ops->get_info) sz =3D ca_ops->get_info(sk, ~0U, &attr, &info); + rcu_read_unlock(); =20 len =3D min_t(unsigned int, len, sz); if (copy_to_sockptr(optlen, &len, sizeof(int))) diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c index 99f68c299..5b457f68a 100644 --- a/net/ipv4/tcp_dctcp.c +++ b/net/ipv4/tcp_dctcp.c @@ -228,7 +228,7 @@ static size_t dctcp_get_info(struct sock *sk, u32 ext, = int *attr, if (ext & (1 << (INET_DIAG_DCTCPINFO - 1)) || ext & (1 << (INET_DIAG_VEGASINFO - 1))) { memset(&info->dctcp, 0, sizeof(info->dctcp)); - if (inet_csk(sk)->icsk_ca_ops !=3D &dctcp_reno) { + if (READ_ONCE(inet_csk(sk)->icsk_ca_ops) !=3D &dctcp_reno) { info->dctcp.dctcp_enabled =3D 1; info->dctcp.dctcp_ce_state =3D (u16) ca->ce_state; info->dctcp.dctcp_alpha =3D ca->dctcp_alpha; --=20 2.43.0