CVE-2026-74392
Received Received - Intake

dm Polling Bypass in Linux Kernel

Publication date: 2026-08-15

Last updated on: 2026-08-15

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: dm: limit target bio polling to one shot dm_poll_bio() is the ->poll_bio() callback for a stacked dm device. The caller only knows about the dm queue, so it may decide to do a spinning poll if it thinks a single queue is being polled. Passing those flags unchanged to the mapped clone lets blk_mq_poll() spin on a target queue from inside dm_poll_bio(). With io_uring IOPOLL on a dm-stripe target this can keep a task in dm_poll_bio() -> bio_poll() -> blk_mq_poll() long enough to trigger an RCU CPU stall, before io_uring gets back to io_iopoll_check() and its need_resched() check. Keep dm's ->poll_bio() bounded by forcing one-shot polling for target bios. The caller can invoke dm_poll_bio() again if it wants to keep polling, and it also gets a chance to reap completions or reschedule between passes.

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Meta Information

Published
2026-08-15
Last Modified
2026-08-15
Generated
2026-08-15
AI Q&A
2026-08-15
EPSS Evaluated
N/A
NVD
CVE-2026-74392
EUVD
EUVD-2026-59539

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves a flaw in device mapper (dm) bio polling. When io_uring IOPOLL is used with a dm-stripe target, the system may enter a long polling loop in dm_poll_bio() that triggers an RCU CPU stall before io_uring can check for rescheduling. The fix limits dm's ->poll_bio() to one-shot polling to prevent this issue.

Detection Guidance

This vulnerability is specific to the Linux kernel's device mapper (dm) subsystem and may not have direct network detection methods. Monitor for RCU CPU stalls or kernel hangs during high I/O operations on dm-stripe targets. Check kernel logs for stall warnings or dm-related errors.

Impact Analysis

This vulnerability could cause system hangs or unresponsiveness due to RCU CPU stalls, leading to degraded performance or crashes. Systems using dm-stripe targets with io_uring IOPOLL may experience instability or require manual intervention to recover.

Mitigation Strategies

Update the Linux kernel to the latest stable version that includes the fix for this vulnerability. If immediate patching is not possible, avoid using io_uring IOPOLL with dm-stripe targets until patched.

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