CVE-2026-89508: RDMA/ucma: Lock the handler in ucma_set_ib_path()

CVE-2026-89508: RDMA/ucma: Lock the handler in ucma_set_ib_path()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

RDMA/ucma: Lock the handler in ucma_set_ib_path()

ucma_set_ib_path() calls ucma_event_handler() straight from the write()
path, without the handler lock that keeps ctx->file stable while a uevent
is queued.  The handler re-reads ctx->file for every dereference:

	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 */

A concurrent ucma_migrate_id() reassigns ctx->file while the SET_OPTION
caller sleeps in mutex_lock(), so the list_add_tail() lands on file B's
event_list while only file A's mutex is held, racing every other user of
that list:

  BUG: KASAN: slab-use-after-free in __list_add_valid_or_report+0x1aa/0x1c0
  Read of size 8 at addr ffff888153c6a418 by task poc_corr/486
  Call Trace:
   __list_add_valid_or_report+0x1aa/0x1c0
   ucma_event_handler+0x1be/0xc00
   ucma_set_ib_path+0x45e/0x710
   ucma_set_option+0x32e/0x590
   ucma_write+0x1f9/0x330
  Allocated by task 505:
   ucma_write_cm_event+0x1a1/0x660
  Freed by task 505:
   kfree+0x1da/0x4c0
   ucma_get_event+0x5d5/0x7e0

The freed object is a ucma_event that another thread dequeued from file B's
list under file B's mutex.  File A's mut is left held on top of that,
wedging its next writer in uninterruptible sleep.

This path needs a bound and address-resolved cm_id, so it requires an RDMA
device to be present.

Take the handler lock around the call.

The Linux kernel CVE team has assigned CVE-2026-89508 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.10 with commit 09e328e47a695b0d346598f5d6593ee598e64885 and fixed in 6.12.109 with commit 764586f8f6180084c5a7d622120f526acc6ce0c9
	Issue introduced in 5.10 with commit 09e328e47a695b0d346598f5d6593ee598e64885 and fixed in 6.18.50 with commit 28ac2dd416482d1c763c4af5d61af465b387fb50
	Issue introduced in 5.10 with commit 09e328e47a695b0d346598f5d6593ee598e64885 and fixed in 7.2.4 with commit 43a7d8ae9f645dc00235cfa4bf57673c20b769f8
	Issue introduced in 5.10 with commit 09e328e47a695b0d346598f5d6593ee598e64885 and fixed in 7.3-rc1 with commit ecbe7d36dc2de07e5dfbb4a8ff5b315ab43de820

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89508
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/infiniband/core/ucma.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/764586f8f6180084c5a7d622120f526acc6ce0c9
	https://git.kernel.org/stable/c/28ac2dd416482d1c763c4af5d61af465b387fb50
	https://git.kernel.org/stable/c/43a7d8ae9f645dc00235cfa4bf57673c20b769f8
	https://git.kernel.org/stable/c/ecbe7d36dc2de07e5dfbb4a8ff5b315ab43de820