ata: libata-scsi: avoid Non-NCQ command starvation

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Summary

CVECVE-2026-45855
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-27 14:16:57 UTC
Updated2026-05-27 14:48:31 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ata: libata-scsi: avoid Non-NCQ command starvation When a non-NCQ command is issued while NCQ commands are being executed, ata_scsi_qc_issue() indicates to the SCSI layer that the command issuing should be deferred by returning SCSI_MLQUEUE_XXX_BUSY. This command deferring is correct and as mandated by the ACS specifications since NCQ and non-NCQ commands cannot be mixed. However, in the case of a host adapter using multiple submission queues, when the target device is under a constant load of NCQ commands, there are no guarantees that requeueing the non-NCQ command will be executed later and it may be deferred again repeatedly as other submission queues can constantly issue NCQ commands from different CPUs ahead of the non-NCQ command. This can lead to very long delays for the execution of non-NCQ commands, and even complete starvation for these commands in the worst case scenario. Since the block layer and the SCSI layer do not distinguish between queueable (NCQ) and non queueable (non-NCQ) commands, libata-scsi SAT implementation must ensure forward progress for non-NCQ commands in the presence of NCQ command traffic. This is similar to what SAS HBAs with a hardware/firmware based SAT implementation do. Implement such forward progress guarantee by limiting requeueing of non-NCQ commands from ata_scsi_qc_issue(): when a non-NCQ command is received and NCQ commands are in-flight, do not force a requeue of the non-NCQ command by returning SCSI_MLQUEUE_XXX_BUSY and instead return 0 to indicate that the command was accepted but hold on to the qc using the new deferred_qc field of struct ata_port. This deferred qc will be issued using the work item deferred_qc_work running the function ata_scsi_deferred_qc_work() once all in-flight commands complete, which is checked with the port qc_defer() callback return value indicating that no further delay is necessary. This check is done using the helper function ata_scsi_schedule_deferred_qc() which is called from ata_scsi_qc_complete(). This thus excludes this mechanism from all internal non-NCQ commands issued by ATA EH. When a port deferred_qc is non NULL, that is, the port has a command waiting for the device queue to drain, the issuing of all incoming commands (both NCQ and non-NCQ) is deferred using the regular busy mechanism. This simplifies the code and also avoids potential denial of service problems if a user issues too many non-NCQ commands. Finally, whenever ata EH is scheduled, regardless of the reason, a deferred qc is always requeued so that it can be retried once EH completes. This is done by calling the function ata_scsi_requeue_deferred_qc() from ata_eh_set_pending(). This avoids the need for any special processing for the deferred qc in case of NCQ error, link or device reset, or device timeout.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected bdb01301f3ea51a59eff252b06643fc1fe843e57 ce22aaed011206fed9cbd8c9c2d44718607f31ee git Not specified
CNA Linux Linux affected bdb01301f3ea51a59eff252b06643fc1fe843e57 888cd7e40adb2ef4af1b4d3b6e2e83ad409ae8c2 git Not specified
CNA Linux Linux affected bdb01301f3ea51a59eff252b06643fc1fe843e57 5d61a38a60e62750526d94663b69b7ac5c7f07a5 git Not specified
CNA Linux Linux affected bdb01301f3ea51a59eff252b06643fc1fe843e57 0ea84089dbf62a92dc7889c79e6b18fc89260808 git Not specified
CNA Linux Linux affected 5.10 Not specified
CNA Linux Linux unaffected 5.10 semver Not specified
CNA Linux Linux unaffected 6.12.77 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.14 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.4 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0ea84089dbf62a92dc7889c79e6b18fc89260808 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ce22aaed011206fed9cbd8c9c2d44718607f31ee 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/888cd7e40adb2ef4af1b4d3b6e2e83ad409ae8c2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5d61a38a60e62750526d94663b69b7ac5c7f07a5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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