CVE-2024-26698

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

hv_netvsc: Fix race condition between netvsc_probe and netvsc_remove

In commit ac5047671758 (hv_netvsc: Disable NAPI before closing the VMBus channel), napi_disable was getting called for all channels, including all subchannels without confirming if they are enabled or not.

This caused hv_netvsc getting hung at napi_disable, when netvsc_probe() has finished running but nvdev->subchan_work has not started yet. netvsc_subchan_work() -> rndis_set_subchannel() has not created the sub-channels and because of that netvsc_sc_open() is not running. netvsc_remove() calls cancel_work_sync(&nvdev->subchan_work), for which netvsc_subchan_work did not run.

netif_napi_add() sets the bit NAPI_STATE_SCHED because it ensures NAPI cannot be scheduled. Then netvsc_sc_open() -> napi_enable will clear the NAPIF_STATE_SCHED bit, so it can be scheduled. napi_disable() does the opposite.

Now during netvsc_device_remove(), when napi_disable is called for those subchannels, napi_disable gets stuck on infinite msleep.

This fix addresses this problem by ensuring that napi_disable() is not getting called for non-enabled NAPI struct. But netif_napi_del() is still necessary for these non-enabled NAPI struct for cleanup purpose.

Call trace: [ 654.559417] task:modprobe state:D stack: 0 pid: 2321 ppid: 1091 flags:0x00004002 [ 654.568030] Call Trace: [ 654.571221] [ 654.573790] __schedule+0x2d6/0x960 [ 654.577733] schedule+0x69/0xf0 [ 654.581214] schedule_timeout+0x87/0x140 [ 654.585463] ? __bpf_trace_tick_stop+0x20/0x20 [ 654.590291] msleep+0x2d/0x40 [ 654.593625] napi_disable+0x2b/0x80 [ 654.597437] netvsc_device_remove+0x8a/0x1f0 [hv_netvsc] [ 654.603935] rndis_filter_device_remove+0x194/0x1c0 [hv_netvsc] [ 654.611101] ? do_wait_intr+0xb0/0xb0 [ 654.615753] netvsc_remove+0x7c/0x120 [hv_netvsc] [ 654.621675] vmbus_remove+0x27/0x40 [hv_vmbus]

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/0e8875de9dad12805ff66e92cd5edea6a421f1cd
• https://git.kernel.org/stable/c/22a77c0f5b8233237731df3288d067af51a2fd7b
• https://git.kernel.org/stable/c/48a8ccccffbae10c91d31fc872db5c31aba07518
• https://git.kernel.org/stable/c/7656372ae190e54e8c8cf1039725a5ea59fdf84a
• https://git.kernel.org/stable/c/9ec807e7b6f5fcf9499f3baa69f254bb239a847f
• https://git.kernel.org/stable/c/e0526ec5360a48ad3ab2e26e802b0532302a7e11
• https://git.kernel.org/stable/c/0e8875de9dad12805ff66e92cd5edea6a421f1cd
• https://git.kernel.org/stable/c/22a77c0f5b8233237731df3288d067af51a2fd7b
• https://git.kernel.org/stable/c/48a8ccccffbae10c91d31fc872db5c31aba07518
• https://git.kernel.org/stable/c/7656372ae190e54e8c8cf1039725a5ea59fdf84a
• https://git.kernel.org/stable/c/9ec807e7b6f5fcf9499f3baa69f254bb239a847f
• https://git.kernel.org/stable/c/e0526ec5360a48ad3ab2e26e802b0532302a7e11
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html