CVE-2025-71088

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> mptcp: fallback earlier on simult connection<br /> <br /> Syzkaller reports a simult-connect race leading to inconsistent fallback<br /> status:<br /> <br /> WARNING: CPU: 3 PID: 33 at net/mptcp/subflow.c:1515 subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1515<br /> Modules linked in:<br /> CPU: 3 UID: 0 PID: 33 Comm: ksoftirqd/3 Not tainted syzkaller #0 PREEMPT(full)<br /> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014<br /> RIP: 0010:subflow_data_ready+0x40b/0x7c0 net/mptcp/subflow.c:1515<br /> Code: 89 ee e8 78 61 3c f6 40 84 ed 75 21 e8 8e 66 3c f6 44 89 fe bf 07 00 00 00 e8 c1 61 3c f6 41 83 ff 07 74 09 e8 76 66 3c f6 90 0b 90 e8 6d 66 3c f6 48 89 df e8 e5 ad ff ff 31 ff 89 c5 89 c6<br /> RSP: 0018:ffffc900006cf338 EFLAGS: 00010246<br /> RAX: 0000000000000000 RBX: ffff888031acd100 RCX: ffffffff8b7f2abf<br /> RDX: ffff88801e6ea440 RSI: ffffffff8b7f2aca RDI: 0000000000000005<br /> RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000007<br /> R10: 0000000000000004 R11: 0000000000002c10 R12: ffff88802ba69900<br /> R13: 1ffff920000d9e67 R14: ffff888046f81800 R15: 0000000000000004<br /> FS: 0000000000000000(0000) GS:ffff8880d69bc000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: 0000560fc0ca1670 CR3: 0000000032c3a000 CR4: 0000000000352ef0<br /> Call Trace:<br /> <br /> tcp_data_queue+0x13b0/0x4f90 net/ipv4/tcp_input.c:5197<br /> tcp_rcv_state_process+0xfdf/0x4ec0 net/ipv4/tcp_input.c:6922<br /> tcp_v6_do_rcv+0x492/0x1740 net/ipv6/tcp_ipv6.c:1672<br /> tcp_v6_rcv+0x2976/0x41e0 net/ipv6/tcp_ipv6.c:1918<br /> ip6_protocol_deliver_rcu+0x188/0x1520 net/ipv6/ip6_input.c:438<br /> ip6_input_finish+0x1e4/0x4b0 net/ipv6/ip6_input.c:489<br /> NF_HOOK include/linux/netfilter.h:318 [inline]<br /> NF_HOOK include/linux/netfilter.h:312 [inline]<br /> ip6_input+0x105/0x2f0 net/ipv6/ip6_input.c:500<br /> dst_input include/net/dst.h:471 [inline]<br /> ip6_rcv_finish net/ipv6/ip6_input.c:79 [inline]<br /> NF_HOOK include/linux/netfilter.h:318 [inline]<br /> NF_HOOK include/linux/netfilter.h:312 [inline]<br /> ipv6_rcv+0x264/0x650 net/ipv6/ip6_input.c:311<br /> __netif_receive_skb_one_core+0x12d/0x1e0 net/core/dev.c:5979<br /> __netif_receive_skb+0x1d/0x160 net/core/dev.c:6092<br /> process_backlog+0x442/0x15e0 net/core/dev.c:6444<br /> __napi_poll.constprop.0+0xba/0x550 net/core/dev.c:7494<br /> napi_poll net/core/dev.c:7557 [inline]<br /> net_rx_action+0xa9f/0xfe0 net/core/dev.c:7684<br /> handle_softirqs+0x216/0x8e0 kernel/softirq.c:579<br /> run_ksoftirqd kernel/softirq.c:968 [inline]<br /> run_ksoftirqd+0x3a/0x60 kernel/softirq.c:960<br /> smpboot_thread_fn+0x3f7/0xae0 kernel/smpboot.c:160<br /> kthread+0x3c2/0x780 kernel/kthread.c:463<br /> ret_from_fork+0x5d7/0x6f0 arch/x86/kernel/process.c:148<br /> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245<br /> <br /> <br /> The TCP subflow can process the simult-connect syn-ack packet after<br /> transitioning to TCP_FIN1 state, bypassing the MPTCP fallback check,<br /> as the sk_state_change() callback is not invoked for * -&gt; FIN_WAIT1<br /> transitions.<br /> <br /> That will move the msk socket to an inconsistent status and the next<br /> incoming data will hit the reported splat.<br /> <br /> Close the race moving the simult-fallback check at the earliest possible<br /> stage - that is at syn-ack generation time.<br /> <br /> About the fixes tags: [2] was supposed to also fix this issue introduced<br /> by [3]. [1] is required as a dependence: it was not explicitly marked as<br /> a fix, but it is one and it has already been backported before [3]. In<br /> other words, this commit should be backported up to [3], including [2]<br /> and [1] if that&amp;#39;s not already there.