CVE-2024-56703

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Fix soft lockups in fib6_select_path under high next hop churn

Soft lockups have been observed on a cluster of Linux-based edge routers

located in a highly dynamic environment. Using the `bird` service, these

routers continuously update BGP-advertised routes due to frequently

changing nexthop destinations, while also managing significant IPv6

traffic. The lockups occur during the traversal of the multipath

circular linked-list in the `fib6_select_path` function, particularly

while iterating through the siblings in the list. The issue typically

arises when the nodes of the linked list are unexpectedly deleted

concurrently on a different core—indicated by their 'next' and

'previous' elements pointing back to the node itself and their reference

count dropping to zero. This results in an infinite loop, leading to a

soft lockup that triggers a system panic via the watchdog timer.

Apply RCU primitives in the problematic code sections to resolve the

issue. Where necessary, update the references to fib6_siblings to

annotate or use the RCU APIs.

Include a test script that reproduces the issue. The script

periodically updates the routing table while generating a heavy load

of outgoing IPv6 traffic through multiple iperf3 clients. It

consistently induces infinite soft lockups within a couple of minutes.

Kernel log:

0 [ffffbd13003e8d30] machine_kexec at ffffffff8ceaf3eb

1 [ffffbd13003e8d90] __crash_kexec at ffffffff8d0120e3

2 [ffffbd13003e8e58] panic at ffffffff8cef65d4

3 [ffffbd13003e8ed8] watchdog_timer_fn at ffffffff8d05cb03

4 [ffffbd13003e8f08] __hrtimer_run_queues at ffffffff8cfec62f

5 [ffffbd13003e8f70] hrtimer_interrupt at ffffffff8cfed756

6 [ffffbd13003e8fd0] __sysvec_apic_timer_interrupt at ffffffff8cea01af

7 [ffffbd13003e8ff0] sysvec_apic_timer_interrupt at ffffffff8df1b83d

-- <IRQ stack> --

8 [ffffbd13003d3708] asm_sysvec_apic_timer_interrupt at ffffffff8e000ecb

[exception RIP: fib6_select_path+299]

RIP: ffffffff8ddafe7b RSP: ffffbd13003d37b8 RFLAGS: 00000287

RAX: ffff975850b43600 RBX: ffff975850b40200 RCX: 0000000000000000

RDX: 000000003fffffff RSI: 0000000051d383e4 RDI: ffff975850b43618

RBP: ffffbd13003d3800 R8: 0000000000000000 R9: ffff975850b40200

R10: 0000000000000000 R11: 0000000000000000 R12: ffffbd13003d3830

R13: ffff975850b436a8 R14: ffff975850b43600 R15: 0000000000000007

ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018

9 [ffffbd13003d3808] ip6_pol_route at ffffffff8ddb030c

10 [ffffbd13003d3888] ip6_pol_route_input at ffffffff8ddb068c

11 [ffffbd13003d3898] fib6_rule_lookup at ffffffff8ddf02b5

12 [ffffbd13003d3928] ip6_route_input at ffffffff8ddb0f47

13 [ffffbd13003d3a18] ip6_rcv_finish_core.constprop.0 at ffffffff8dd950d0

14 [ffffbd13003d3a30] ip6_list_rcv_finish.constprop.0 at ffffffff8dd96274

15 [ffffbd13003d3a98] ip6_sublist_rcv at ffffffff8dd96474

16 [ffffbd13003d3af8] ipv6_list_rcv at ffffffff8dd96615

17 [ffffbd13003d3b60] __netif_receive_skb_list_core at ffffffff8dc16fec

18 [ffffbd13003d3be0] netif_receive_skb_list_internal at ffffffff8dc176b3

19 [ffffbd13003d3c50] napi_gro_receive at ffffffff8dc565b9

20 [ffffbd13003d3c80] ice_receive_skb at ffffffffc087e4f5 [ice]

21 [ffffbd13003d3c90] ice_clean_rx_irq at ffffffffc0881b80 [ice]

22 [ffffbd13003d3d20] ice_napi_poll at ffffffffc088232f [ice]

23 [ffffbd13003d3d80] __napi_poll at ffffffff8dc18000

24 [ffffbd13003d3db8] net_rx_action at ffffffff8dc18581

25 [ffffbd13003d3e40] __do_softirq at ffffffff8df352e9

26 [ffffbd13003d3eb0] run_ksoftirqd at ffffffff8ceffe47

27 [ffffbd13003d3ec0] smpboot_thread_fn at ffffffff8cf36a30

28 [ffffbd13003d3ee8] kthread at ffffffff8cf2b39f

29 [ffffbd13003d3f28] ret_from_fork at ffffffff8ce5fa64

30 [ffffbd13003d3f50] ret_from_fork_asm at ffffffff8ce03cbb