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CVE-2025-21806 Affecting kernel-rt package, versions *

Severity

 Recommended
0.0
medium
0
10

Based on Red Hat Enterprise Linux security rating.

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  • Snyk IDSNYK-RHEL7-KERNELRT-9032053
  • published2 Mar 2025
  • disclosed27 Feb 2025
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Introduced: 27 Feb 2025

NewCVE-2025-21806  (opens in a new tab)

How to fix?

There is no fixed version for RHEL:7 kernel-rt.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-rt package and not the kernel-rt package as distributed by RHEL. See How to fix? for RHEL:7 relevant fixed versions and status.

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).

CVSS Scores

version 3.1