cxl/port: Fix use after free of parent_port in cxl_detach_ep()

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Summary

CVECVE-2026-31530
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-22 14:16:53 UTC
Updated2026-04-22 14:16:53 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: cxl/port: Fix use after free of parent_port in cxl_detach_ep() cxl_detach_ep() is called during bottom-up removal when all CXL memory devices beneath a switch port have been removed. For each port in the hierarchy it locks both the port and its parent, removes the endpoint, and if the port is now empty, marks it dead and unregisters the port by calling delete_switch_port(). There are two places during this work where the parent_port may be used after freeing: First, a concurrent detach may have already processed a port by the time a second worker finds it via bus_find_device(). Without pinning parent_port, it may already be freed when we discover port->dead and attempt to unlock the parent_port. In a production kernel that's a silent memory corruption, with lock debug, it looks like this: []DEBUG_LOCKS_WARN_ON(__owner_task(owner) != get_current()) []WARNING: kernel/locking/mutex.c:949 at __mutex_unlock_slowpath+0x1ee/0x310 []Call Trace: []mutex_unlock+0xd/0x20 []cxl_detach_ep+0x180/0x400 [cxl_core] []devm_action_release+0x10/0x20 []devres_release_all+0xa8/0xe0 []device_unbind_cleanup+0xd/0xa0 []really_probe+0x1a6/0x3e0 Second, delete_switch_port() releases three devm actions registered against parent_port. The last of those is unregister_port() and it calls device_unregister() on the child port, which can cascade. If parent_port is now also empty the device core may unregister and free it too. So by the time delete_switch_port() returns, parent_port may be free, and the subsequent device_unlock(&parent_port->dev) operates on freed memory. The kernel log looks same as above, with a different offset in cxl_detach_ep(). Both of these issues stem from the absence of a lifetime guarantee between a child port and its parent port. Establish a lifetime rule for ports: child ports hold a reference to their parent device until release. Take the reference when the port is allocated and drop it when released. This ensures the parent is valid for the full lifetime of the child and eliminates the use after free window in cxl_detach_ep(). This is easily reproduced with a reload of cxl_acpi in QEMU with CXL devices present.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 2345df54249c6fb7779e2a72b427ee79ed3eaad5 d216a4bd138eb57cc4ae7c43b2f709e3482af7e2 git Not specified
CNA Linux Linux affected 2345df54249c6fb7779e2a72b427ee79ed3eaad5 2c32141462045cf93d54a5146a0ba572b83533dd git Not specified
CNA Linux Linux affected 2345df54249c6fb7779e2a72b427ee79ed3eaad5 f7dc6f381a1e5f068333f1faa9265d6af1df4235 git Not specified
CNA Linux Linux affected 2345df54249c6fb7779e2a72b427ee79ed3eaad5 19d2f0b97a131198efc2c4ca3eb7f980bba8c2b4 git Not specified
CNA Linux Linux affected 6.3 Not specified
CNA Linux Linux unaffected 6.3 semver Not specified
CNA Linux Linux unaffected 6.12.80 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.21 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.11 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/2c32141462045cf93d54a5146a0ba572b83533dd 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d216a4bd138eb57cc4ae7c43b2f709e3482af7e2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/19d2f0b97a131198efc2c4ca3eb7f980bba8c2b4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f7dc6f381a1e5f068333f1faa9265d6af1df4235 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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