UBUNTU-CVE-2025-21681
In the Linux kernel, the following vulnerability has been resolved: openvswitch: fix lockup on tx to unregistering netdev with carrier Commit in a fixes tag attempted to fix the issue in the following sequence of calls: do_output -> ovs_vport_send -> dev_queue_xmit -> __dev_queue_xmit -> netdev_core_pick_tx -> skb_tx_hash When device is unregistering, the 'dev->real_num_tx_queues' goes to zero and the 'while (unlikely(hash >= qcount))' loop inside the 'skb_tx_hash' becomes infinite, locking up the core forever. But unfortunately, checking just the carrier status is not enough to fix the issue, because some devices may still be in unregistering state while reporting carrier status OK. One example of such device is a net/dummy. It sets carrier ON on start, but it doesn't implement .ndo_stop to set the carrier off. And it makes sense, because dummy doesn't really have a carrier. Therefore, while this device is unregistering, it's still easy to hit the infinite loop in the skb_tx_hash() from the OVS datapath. There might be other drivers that do the same, but dummy by itself is important for the OVS ecosystem, because it is frequently used as a packet sink for tcpdump while debugging OVS deployments. And when the issue is hit, the only way to recover is to reboot. Fix that by also checking if the device is running. The running state is handled by the net core during unregistering, so it covers unregistering case better, and we don't really need to send packets to devices that are not running anyway. While only checking the running state might be enough, the carrier check is preserved. The running and the carrier states seem disjoined throughout the code and different drivers. And other core functions like __dev_direct_xmit() check both before attempting to transmit a packet. So, it seems safer to check both flags in OVS as well.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
24 explicit affected versions
10 explicit affected versions
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22 explicit affected versions
7 explicit affected versions
19 explicit affected versions
13 explicit affected versions
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35 explicit affected versions
18 explicit affected versions
24 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
29 explicit affected versions
1 explicit affected versions
21 explicit affected versions
16 explicit affected versions
10 explicit affected versions
25 explicit affected versions
3 explicit affected versions
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12 explicit affected versions
2 explicit affected versions
12 explicit affected versions
14 explicit affected versions
1 explicit affected versions
7 explicit affected versions
2 explicit affected versions
12 explicit affected versions
12 explicit affected versions
19 explicit affected versions
16 explicit affected versions
11 explicit affected versions
10 explicit affected versions
37 explicit affected versions
3 explicit affected versions
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10 explicit affected versions
26 explicit affected versions
13 explicit affected versions
29 explicit affected versions
13 explicit affected versions
18 explicit affected versions
19 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
1 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
10 explicit affected versions
26 explicit affected versions
23 explicit affected versions
14 explicit affected versions
24 explicit affected versions
13 explicit affected versions
24 explicit affected versions
16 explicit affected versions
27 explicit affected versions
3 explicit affected versions
2 explicit affected versions
51 explicit affected versions
11 explicit affected versions
21 explicit affected versions
12 explicit affected versions
27 explicit affected versions
44 explicit affected versions
20 explicit affected versions
8 explicit affected versions
5 explicit affected versions
8 explicit affected versions
10 explicit affected versions
2 explicit affected versions
23 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
2 explicit affected versions
10 explicit affected versions
12 explicit affected versions
80 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
28 explicit affected versions
14 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
17 explicit affected versions
7 explicit affected versions
7 explicit affected versions
4 explicit affected versions
1 explicit affected versions
13 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
22 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
17 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: openvswitch: fix lockup on tx to unregistering netdev with carrier Commit in a fixes tag attempted to fix the issue in the following sequence of calls: do_output -> ovs_vport_send -> dev_queue_xmit -> __dev_queue_xmit -> netdev_core_pick_tx -> skb_tx_hash When device is unregistering, the 'dev->real_num_tx_queues' goes to zero and the 'while (unlikely(hash >= qcount))' loop inside the 'skb_tx_hash' becomes infinite, locking up the core forever. But unfortunately, checking just the carrier status is not enough to fix the issue, because some devices may still be in unregistering state while reporting carrier status OK. One example of such device is a net/dummy. It sets carrier ON on start, but it doesn't implement .ndo_stop to set the carrier off. And it makes sense, because dummy doesn't really have a carrier. Therefore, while this device is unregistering, it's still easy to hit the infinite loop in the skb_tx_hash() from the OVS datapath. There might be other drivers that do the same, but dummy by itself is important for the OVS ecosystem, because it is frequently used as a packet sink for tcpdump while debugging OVS deployments. And when the issue is hit, the only way to recover is to reboot. Fix that by also checking if the device is running. The running state is handled by the net core during unregistering, so it covers unregistering case better, and we don't really need to send packets to devices that are not running anyway. While only checking the running state might be enough, the carrier check is preserved. The running and the carrier states seem disjoined throughout the code and different drivers. And other core functions like __dev_direct_xmit() check both before attempting to transmit a packet. So, it seems safer to check both flags in OVS as well.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/47e55e4b410f7d552e43011baa5be1aab4093990
- https://git.kernel.org/stable/c/47e55e4b410f7d552e43011baa5be1aab4093990
- https://git.kernel.org/stable/c/82f433e8dd0629e16681edf6039d094b5518d8ed
- https://git.kernel.org/stable/c/ea966b6698785fb9cd0fdb867acd91b222e4723f
- https://git.kernel.org/stable/c/ea9e990356b7bee95440ba0e6e83cc4d701afaca
- https://ubuntu.com/security/CVE-2025-21681
- https://ubuntu.com/security/notices/USN-7445-1
- https://ubuntu.com/security/notices/USN-7448-1
- https://ubuntu.com/security/notices/USN-7595-1
- https://ubuntu.com/security/notices/USN-7595-2
- https://ubuntu.com/security/notices/USN-7595-3
- https://ubuntu.com/security/notices/USN-7595-4
- https://ubuntu.com/security/notices/USN-7595-5
- https://ubuntu.com/security/notices/USN-7596-1
- https://ubuntu.com/security/notices/USN-7596-2
- https://ubuntu.com/security/notices/USN-7653-1
- https://www.cve.org/CVERecord?id=CVE-2025-21681