Описание
In the Linux kernel, the following vulnerability has been resolved: tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink(). Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """ The commit 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not to call del_timer_sync() from reqsk_timer_handler(), but it introduced a small race window. Before the timer is called, expire_timers() calls detach_timer(timer, true) to clear timer->entry.pprev and marks it as not pending. If reqsk_queue_unlink() checks timer_pending() just after expire_timers() calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will continue running and send multiple SYN+ACKs until it expires. The reported UAF could happen if req->sk is close()d earlier than the timer expiration, which is 63s by default. The scenario would be
- inet_csk_complete_hashdance() calls inet_csk_reqsk_queue_drop(), but del_timer_sync() is missed
- reqsk timer is executed and scheduled again
- req->sk is accept()ed and reqsk_put() decrements rsk_refcnt, but reqsk timer still has another one, and inet_csk_accept() does not clear req->sk for non-TFO sockets
- sk is close()d
- reqsk timer is executed again, and BPF touches req->sk
Let's not use timer_pending() by passing the caller context to
__inet_csk_reqsk_queue_drop().
Note that reqsk timer is pinned, so the issue does not happen in most
use cases. [1]
[0]
BUG: KFENCE: use-after-free read in bpf_sk_storage_get_tracing+0x2e/0x1b0
Use-after-free read at 0x00000000a891fb3a (in kfence-#1):
bpf_sk_storage_get_tracing+0x2e/0x1b0
bpf_prog_5ea3e95db6da0438_tcp_retransmit_synack+0x1d20/0x1dda
bpf_trace_run2+0x4c/0xc0
tcp_rtx_synack+0xf9/0x100
reqsk_timer_handler+0xda/0x3d0
run_timer_softirq+0x292/0x8a0
irq_exit_rcu+0xf5/0x320
sysvec_apic_timer_interrupt+0x6d/0x80
asm_sysvec_apic_timer_interrupt+0x16/0x20
intel_idle_irq+0x5a/0xa0
cpuidle_enter_state+0x94/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb
kfence-#1: 0x00000000a72cc7b6-0x00000000d97616d9, size=2376, cache=TCPv6
allocated by task 0 on cpu 9 at 260507.901592s:
sk_prot_alloc+0x35/0x140
sk_clone_lock+0x1f/0x3f0
inet_csk_clone_lock+0x15/0x160
tcp_create_openreq_child+0x1f/0x410
tcp_v6_syn_recv_sock+0x1da/0x700
tcp_check_req+0x1fb/0x510
tcp_v6_rcv+0x98b/0x1420
ipv6_list_rcv+0x2258/0x26e0
napi_complete_done+0x5b1/0x2990
mlx5e_napi_poll+0x2ae/0x8d0
net_rx_action+0x13e/0x590
irq_exit_rcu+0xf5/0x320
common_interrupt+0x80/0x90
asm_common_interrupt+0x22/0x40
cpuidle_enter_state+0xfb/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb
freed by task 0 on cpu 9 at 260507.927527s:
rcu_core_si+0x4ff/0xf10
irq_exit_rcu+0xf5/0x320
sysvec_apic_timer_interrupt+0x6d/0x80
asm_sysvec_apic_timer_interrupt+0x16/0x20
cpuidle_enter_state+0xfb/0x273
cpu_startup_entry+0x15e/0x260
start_secondary+0x8a/0x90
secondary_startup_64_no_verify+0xfa/0xfb
A use-after-free (UAF) vulnerability was found and fixed in the Linux kernel's TCP subsystem related to request socket (reqsk) timers during handshake handling. This issue stems from a race condition caused by relying ontimer_pending()inreqsk_queue_unlink(). This could result in the timer continuing to run after the socket (req->sk) is freed, allowing BPF programs to access invalid memory.
Отчет
This vulnerability is classified as moderate severity rather than important because the issue primarily affects a narrow set of conditions, notably when BPF programs are involved in tracing TCP retransmissions. In most scenarios, the reqsk timer is pinned and the race condition is unlikely to be triggered. Additionally, the problem only occurs if the request socket (req->sk) is closed while the timer is still pending, which is an uncommon sequence of events. While the potential for a use-after-free (UAF) exists, it requires specific timing and conditions to exploit, limiting its overall risk and impact on typical systems.
Меры по смягчению последствий
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 6 | kernel | Out of support scope | ||
| Red Hat Enterprise Linux 7 | kernel | Out of support scope | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Out of support scope | ||
| Red Hat Enterprise Linux 8 | kernel | Affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Will not fix | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Affected | ||
| Red Hat Enterprise Linux 9 | kernel | Fixed | RHSA-2025:0578 | 22.01.2025 |
| Red Hat Enterprise Linux 9 | kernel | Fixed | RHSA-2025:0578 | 22.01.2025 |
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Дополнительная информация
Статус:
7 High
CVSS3
Связанные уязвимости
In the Linux kernel, the following vulnerability has been resolved: tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink(). Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """ The commit 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not to call del_timer_sync() from reqsk_timer_handler(), but it introduced a small race window. Before the timer is called, expire_timers() calls detach_timer(timer, true) to clear timer->entry.pprev and marks it as not pending. If reqsk_queue_unlink() checks timer_pending() just after expire_timers() calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will continue running and send multiple SYN+ACKs until it expires. The r...
In the Linux kernel, the following vulnerability has been resolved: tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink(). Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """ The commit 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not to call del_timer_sync() from reqsk_timer_handler(), but it introduced a small race window. Before the timer is called, expire_timers() calls detach_timer(timer, true) to clear timer->entry.pprev and marks it as not pending. If reqsk_queue_unlink() checks timer_pending() just after expire_timers() calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will continue running and send multiple SYN+ACKs until it expire
In the Linux kernel, the following vulnerability has been resolved: t ...
In the Linux kernel, the following vulnerability has been resolved: tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink(). Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """ The commit 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not to call del_timer_sync() from reqsk_timer_handler(), but it introduced a small race window. Before the timer is called, expire_timers() calls detach_timer(timer, true) to clear timer->entry.pprev and marks it as not pending. If reqsk_queue_unlink() checks timer_pending() just after expire_timers() calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will continue running and send multiple SYN+ACKs until it exp...
7 High
CVSS3