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Fri, 21 Aug 2026 11:25:17 -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, yhs@fb.com, kafai@fb.com, andriin@fb.com, ast@kernel.org, netdev@vger.kernel.org, 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 1/2] tcp: fix use-after-free in do_tcp_getsockopt(TCP_CONGESTION) Date: Fri, 21 Aug 2026 14:24:48 -0400 Message-ID: <20260821182449.79785-2-blbllhy@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260821182449.79785-1-blbllhy@gmail.com> References: <20260821182449.79785-1-blbllhy@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 and copying the name to a stack buffer before releasing the lock. Fixes: 0baf26b0fcd7 ("bpf: tcp: Support tcp_congestion_ops in bpf") Reported-by: AutonomousCodeSecurity@microsoft.com Reported-by: Xiang Mei (Microsoft) Reported-by: Cen Zhang (Microsoft) Cc: stable@vger.kernel.org Signed-off-by: Cen Zhang (Microsoft) --- The unsynchronized icsk_ca_ops load also constitutes a data race. READ_ONCE()/WRITE_ONCE() annotations are intentionally left to a separate change; related TCP annotation work is available at: https://lore.kernel.org/all/20260416200319.3608680-1-edumazet@google.com/ net/ipv4/tcp.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index b4237d0e994d..7360ff718f1d 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -4577,16 +4577,23 @@ 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, 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; -- 2.55.0