CVE-2024-40976

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

drm/lima: mask irqs in timeout path before hard reset

There is a race condition in which a rendering job might take just long enough to trigger the drm sched job timeout handler but also still complete before the hard reset is done by the timeout handler. This runs into race conditions not expected by the timeout handler. In some very specific cases it currently may result in a refcount imbalance on lima_pm_idle, with a stack dump such as:

[10136.669170] WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/lima/lima_devfreq.c:205 lima_devfreq_record_idle+0xa0/0xb0 … [10136.669459] pc : lima_devfreq_record_idle+0xa0/0xb0 … [10136.669628] Call trace: [10136.669634] lima_devfreq_record_idle+0xa0/0xb0 [10136.669646] lima_sched_pipe_task_done+0x5c/0xb0 [10136.669656] lima_gp_irq_handler+0xa8/0x120 [10136.669666] __handle_irq_event_percpu+0x48/0x160 [10136.669679] handle_irq_event+0x4c/0xc0

We can prevent that race condition entirely by masking the irqs at the beginning of the timeout handler, at which point we give up on waiting for that job entirely. The irqs will be enabled again at the next hard reset which is already done as a recovery by the timeout handler.

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/03e7b2f7ae4c0ae5fb8e4e2454ba4008877f196a
• https://git.kernel.org/stable/c/58bfd311c93d66d8282bf21ebbf35cc3bb8ad9db
• https://git.kernel.org/stable/c/70aa1f2dec46b6fdb5f6b9f37b6bfa4a4dee0d3a
• https://git.kernel.org/stable/c/9fd8ddd23793a50dbcd11c6ba51f437f1ea7d344
• https://git.kernel.org/stable/c/a421cc7a6a001b70415aa4f66024fa6178885a14
• https://git.kernel.org/stable/c/bdbc4ca77f5eaac15de7230814253cddfed273b1
• https://git.kernel.org/stable/c/03e7b2f7ae4c0ae5fb8e4e2454ba4008877f196a
• https://git.kernel.org/stable/c/58bfd311c93d66d8282bf21ebbf35cc3bb8ad9db
• https://git.kernel.org/stable/c/70aa1f2dec46b6fdb5f6b9f37b6bfa4a4dee0d3a
• https://git.kernel.org/stable/c/9fd8ddd23793a50dbcd11c6ba51f437f1ea7d344
• https://git.kernel.org/stable/c/a421cc7a6a001b70415aa4f66024fa6178885a14
• https://git.kernel.org/stable/c/bdbc4ca77f5eaac15de7230814253cddfed273b1