CVE-2025-39955

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> tcp: Clear tcp_sk(sk)-&gt;fastopen_rsk in tcp_disconnect().<br /> <br /> syzbot reported the splat below where a socket had tcp_sk(sk)-&gt;fastopen_rsk<br /> in the TCP_ESTABLISHED state. [0]<br /> <br /> syzbot reused the server-side TCP Fast Open socket as a new client before<br /> the TFO socket completes 3WHS:<br /> <br /> 1. accept()<br /> 2. connect(AF_UNSPEC)<br /> 3. connect() to another destination<br /> <br /> As of accept(), sk-&gt;sk_state is TCP_SYN_RECV, and tcp_disconnect() changes<br /> it to TCP_CLOSE and makes connect() possible, which restarts timers.<br /> <br /> Since tcp_disconnect() forgot to clear tcp_sk(sk)-&gt;fastopen_rsk, the<br /> retransmit timer triggered the warning and the intended packet was not<br /> retransmitted.<br /> <br /> Let&amp;#39;s call reqsk_fastopen_remove() in tcp_disconnect().<br /> <br /> [0]:<br /> WARNING: CPU: 2 PID: 0 at net/ipv4/tcp_timer.c:542 tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))<br /> Modules linked in:<br /> CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Not tainted 6.17.0-rc5-g201825fb4278 #62 PREEMPT(voluntary)<br /> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014<br /> RIP: 0010:tcp_retransmit_timer (net/ipv4/tcp_timer.c:542 (discriminator 7))<br /> Code: 41 55 41 54 55 53 48 8b af b8 08 00 00 48 89 fb 48 85 ed 0f 84 55 01 00 00 0f b6 47 12 3c 03 74 0c 0f b6 47 12 3c 04 74 04 90 0b 90 48 8b 85 c0 00 00 00 48 89 ef 48 8b 40 30 e8 6a 4f 06 3e<br /> RSP: 0018:ffffc900002f8d40 EFLAGS: 00010293<br /> RAX: 0000000000000002 RBX: ffff888106911400 RCX: 0000000000000017<br /> RDX: 0000000002517619 RSI: ffffffff83764080 RDI: ffff888106911400<br /> RBP: ffff888106d5c000 R08: 0000000000000001 R09: ffffc900002f8de8<br /> R10: 00000000000000c2 R11: ffffc900002f8ff8 R12: ffff888106911540<br /> R13: ffff888106911480 R14: ffff888106911840 R15: ffffc900002f8de0<br /> FS: 0000000000000000(0000) GS:ffff88907b768000(0000) knlGS:0000000000000000<br /> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033<br /> CR2: 00007f8044d69d90 CR3: 0000000002c30003 CR4: 0000000000370ef0<br /> Call Trace:<br /> <br /> tcp_write_timer (net/ipv4/tcp_timer.c:738)<br /> call_timer_fn (kernel/time/timer.c:1747)<br /> __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2372)<br /> timer_expire_remote (kernel/time/timer.c:2385 kernel/time/timer.c:2376 kernel/time/timer.c:2135)<br /> tmigr_handle_remote_up (kernel/time/timer_migration.c:944 kernel/time/timer_migration.c:1035)<br /> __walk_groups.isra.0 (kernel/time/timer_migration.c:533 (discriminator 1))<br /> tmigr_handle_remote (kernel/time/timer_migration.c:1096)<br /> handle_softirqs (./arch/x86/include/asm/jump_label.h:36 ./include/trace/events/irq.h:142 kernel/softirq.c:580)<br /> irq_exit_rcu (kernel/softirq.c:614 kernel/softirq.c:453 kernel/softirq.c:680 kernel/softirq.c:696)<br /> sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1050 (discriminator 35) arch/x86/kernel/apic/apic.c:1050 (discriminator 35))<br />