# CVE-2026-89507

## Summary

- **CVE ID:** CVE-2026-89507
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## Description

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

RDMA/ucma: Lock the handler in ucma_write_cm_event()

ctx->file may only be changed under the handler lock and the xa_lock, which
is what stops uevents being queued for a ctx while ucma_migrate_id() moves
it to another file.  The CM core takes that lock before invoking
ucma_event_handler(), but the write() paths that queue uevents themselves
do not.

ucma_write_cm_event() re-reads ctx->file for each of its four dereferences,
so ucma_migrate_id() can swap it mid-sequence:

	mutex_lock(&ctx->file->mut);			/* file A */
	list_add_tail(&uevent->list, &ctx->file->event_list);	/* file B */
	mutex_unlock(&ctx->file->mut);			/* file B */
	wake_up_interruptible(&ctx->file->poll_wait);	/* file B */

The window is the mutex_lock() itself: the writer sleeps in it while the
migration reassigns ctx->file.  The list_add_tail() then runs on file B's
event_list holding only file A's mutex:

  list_add corruption. prev->next should be next (ffff888101320f30),
    but was ffff88814a08c418. (prev=ffff88814a075c18).
  kernel BUG at lib/list_debug.c:32!
  Call Trace:
   ucma_write_cm_event+0x36e/0x5e0

and file A's mut is left held forever, wedging its next writer in D state.
The uevent is also stranded on a list ucma_cleanup_ctx_events() will not
walk, so it outlives its context.  /dev/infiniband/rdma_cm is 0666 and no
RDMA device is involved, so an unprivileged user reaches all of this.

Take the handler lock, as ucma_cleanup_mc_events() does; ctx->cm_id is
pinned by the ucma_get_ctx() reference.

## Affected Products

- Linux — Linux (a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5)
- Linux — Linux (6.18)
- Linux — Linux (0)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/4f8bb11dd2ff365e7cff1c9964ab4607292d364e)
- [CNA](https://git.kernel.org/stable/c/0be1955040a2eceed0ecfc387fdc92305411d273)
- [CNA](https://git.kernel.org/stable/c/f4cc21c6a8e9d392871477f9fd98d68e5ad80272)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.13%
- **EPSS Percentile:** 2.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._