CVE-2026-53331: slimbus: qcom-ngd-ctrl: Avoid ABBA on tx_lock/ctrl->lock
In the Linux kernel, the following vulnerability has been resolved:
slimbus: qcom-ngd-ctrl: Avoid ABBA on txlock/ctrl->lock
During the SSR/PDR down notification the txlock is taken with the intent to provide synchronization with active DMA transfers.
But during this period qcomslimngddown() is invoked, which ends up in slimreportabsent(), which takes the slimcontroller lock. In multiple other codepaths these two locks are taken in the opposite order (i.e. slimcontroller then txlock).
The result is a lockdep splat, and a possible deadlock:
rprocctl/449 is trying to acquire lock: ffff00009793e620 (&ctrl->lock){+.+.}-{4:4}, at: slimreportabsent (drivers/slimbus/core.c:322) slimbus
but task is already holding lock: ffff00009793fb50 (&ctrl->txlock){+.+.}-{4:4}, at: qcomslimngdssrpdrnotify (drivers/slimbus/qcom-ngd-ctrl.c:1475) slimqcomngdctrl
which lock already depends on the new lock.
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&ctrl->txlock); lock(&ctrl->lock); lock(&ctrl->txlock); lock(&ctrl->lock);
The assumption is that the comment refers to the desire to not call qcomslimngdexitdma() while we have an ongoing DMA TX transaction. But any such transaction is initiated and completed within a single qcomslimngdxfermsg().
Prior to calling qcomslimngdexitdma() the slimcontroller is torn down, all child devices are notified that the slimbus is gone and the child devices are removed.
Stop taking the txlock in qcomslimngdssrpdrnotify() to avoid the deadlock.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 6.8.0-1070.78 - Upgrade
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ubuntu/linux-gketo a version that resolves this vulnerability.Fixed in 6.8.0-1065.73 - Upgrade
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Event History
Frequently Asked Questions
Which deployments are in scope?
The affected software list includes Ubuntu linux, linux-realtime, linux-azure, linux-gcp, linux-azure-fde, linux-riscv, linux-gke, and linux-aws kernel packages. The issue is in the Qualcomm NGD SlimBus controller path.
What conditions are needed for the deadlock risk?
The risk arises during an SSR/PDR down notification when the transmit lock is held and the notification path reaches slim_report_absent(), which takes the SlimBus controller lock. A concurrent path that takes the controller lock before the transmit lock can create the opposing lock order.
How might an affected system show this problem?
Kernel lockdep can report a lock-order violation involving ctrl->tx_lock and ctrl->lock, with functions including qcom_slim_ngd_ssr_pdr_notify() and slim_report_absent(). The described outcome is a possible deadlock.