CVE-2025-21806Medium· 5.5▾ SunlitIn the Linux kernel, the following vulnerability has been resolved: net: let net.core.dev_weight always be non-zero The following problem was encountered during stability test: (NULL net_device): NAPI poll function process_backlog+0x0…
▾ Sunlit zone — Low / medium · no exploitation signal
impact 30.3 · likelihood 0 · exploitation 0
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Exploit-prediction probability, daily snapshots since Oct 15.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
0.2% → 0.2%
In the Linux kernel, the following vulnerability has been resolved:
net: let net.core.dev_weight always be non-zero
The following problem was encountered during stability test:
(NULL net_device): NAPI poll function process_backlog+0x0/0x530
returned 1, exceeding its budget of 0.
------------[ cut here ]------------
list_add double add: new=ffff88905f746f48, prev=ffff88905f746f48,
next=ffff88905f746e40.
WARNING: CPU: 18 PID: 5462 at lib/list_debug.c:35
__list_add_valid_or_report+0xf3/0x130
CPU: 18 UID: 0 PID: 5462 Comm: ping Kdump: loaded Not tainted 6.13.0-rc7+
RIP: 0010:__list_add_valid_or_report+0xf3/0x130
Call Trace:
? __warn+0xcd/0x250
? __list_add_valid_or_report+0xf3/0x130
enqueue_to_backlog+0x923/0x1070
netif_rx_internal+0x92/0x2b0
__netif_rx+0x15/0x170
loopback_xmit+0x2ef/0x450
dev_hard_start_xmit+0x103/0x490
__dev_queue_xmit+0xeac/0x1950
ip_finish_output2+0x6cc/0x1620
ip_output+0x161/0x270
ip_push_pending_frames+0x155/0x1a0
raw_sendmsg+0xe13/0x1550
__sys_sendto+0x3bf/0x4e0
__x64_sys_sendto+0xdc/0x1b0
do_syscall_64+0x5b/0x170
entry_SYSCALL_64_after_hwframe+0x76/0x7e
The reproduction command is as follows: sysctl -w net.core.dev_weight=0 ping 127.0.0.1
This is because when the napi's weight is set to 0, process_backlog() may return 0 and clear the NAPI_STATE_SCHED bit of napi->state, causing this napi to be re-polled in net_rx_action() until __do_softirq() times out. Since the NAPI_STATE_SCHED bit has been cleared, napi_schedule_rps() can be retriggered in enqueue_to_backlog(), causing this issue.
Making the napi's weight always non-zero solves this problem.
Triggering this issue requires system-wide admin (setting is not namespaced).
linux_kernel >= 2.6.13, < 5.4.291linux_kernel >= 5.5, < 5.10.235linux_kernel >= 5.11, < 5.15.179linux_kernel >= 5.16, < 6.1.129linux_kernel >= 6.2, < 6.6.76linux_kernel >= 6.7, < 6.12.13linux_kernel >= 6.13, < 6.13.2linux_kernel = 2.6.12Upgrade past the affected range:
linux_kernel 6.13.2Connected by shared product, vendor, weakness, or advisory.
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