CVE-2026-53331

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

slimbus: qcom-ngd-ctrl: Avoid ABBA on tx_lock/ctrl->lock

During the SSR/PDR down notification the tx_lock is taken with the intent to provide synchronization with active DMA transfers.

But during this period qcom_slim_ngd_down() is invoked, which ends up in slim_report_absent(), which takes the slim_controller lock. In multiple other codepaths these two locks are taken in the opposite order (i.e. slim_controller then tx_lock).

The result is a lockdep splat, and a possible deadlock:

rprocctl/449 is trying to acquire lock: ffff00009793e620 (&ctrl->lock){+.+.}-{4:4}, at: slim_report_absent (drivers/slimbus/core.c:322) slimbus

but task is already holding lock: ffff00009793fb50 (&ctrl->tx_lock){+.+.}-{4:4}, at: qcom_slim_ngd_ssr_pdr_notify (drivers/slimbus/qcom-ngd-ctrl.c:1475) slim_qcom_ngd_ctrl

which lock already depends on the new lock.

Possible unsafe locking scenario:

    CPU0                    CPU1
    ----                    ----

lock(&ctrl->tx_lock); lock(&ctrl->lock); lock(&ctrl->tx_lock); lock(&ctrl->lock);

The assumption is that the comment refers to the desire to not call qcom_slim_ngd_exit_dma() while we have an ongoing DMA TX transaction. But any such transaction is initiated and completed within a single qcom_slim_ngd_xfer_msg().

Prior to calling qcom_slim_ngd_exit_dma() the slim_controller is torn down, all child devices are notified that the slimbus is gone and the child devices are removed.

Stop taking the tx_lock in qcom_slim_ngd_ssr_pdr_notify() to avoid the deadlock.

Affected Software

References

• https://git.kernel.org/stable/c/3d1561537237c6cc1db76155183d8bbdac2339f0
• https://git.kernel.org/stable/c/55f2ea9ff83cc27a85526b14bc9b32f96a08d6ec
• https://git.kernel.org/stable/c/9708eb50fd7343145b422be852f890212155d845
• https://git.kernel.org/stable/c/9f0d45d509b434c54da10e01f4ef8086e4583401
• https://git.kernel.org/stable/c/aad4337a21b9ad3ae8d668fa8678d05e26ecbaa8
• https://git.kernel.org/stable/c/d54a221b0f3cd9e1f03f18104be34e02a8258fae
• https://git.kernel.org/stable/c/dc4d5c57e012c2c669793deb1515a57bbc6bf5dd