CVE-2025-38211: kernel: RDMA/iwcm: Fix use-after-free of work objects after cm_id destruction
Component: kernel
Severity: Moderate
CWE: CWE-416 (Use After Free)
CVSS v3: 7.3 (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H)
Public date: 2025-07-04T00:00:00+00:00

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

RDMA/iwcm: Fix use-after-free of work objects after cm_id destruction

The commit 59c68ac31e15 ("iw_cm: free cm_id resources on the last
deref") simplified cm_id resource management by freeing cm_id once all
references to the cm_id were removed. The references are removed either
upon completion of iw_cm event handlers or when the application destroys
the cm_id. This commit introduced the use-after-free condition where
cm_id_private object could still be in use by event handler works during
the destruction of cm_id. The commit aee2424246f9 ("RDMA/iwcm: Fix a
use-after-free related to destroying CM IDs") addressed this use-after-
free by flushing all pending works at the cm_id destruction.

However, still another use-after-free possibility remained. It happens
with the work objects allocated for each cm_id_priv within
alloc_work_entries() during cm_id creation, and subsequently freed in
dealloc_work_entries() once all references to the cm_id are removed.
If the cm_id's last reference is decremented in the event handler work,
the work object for the work itself gets removed, and causes the use-
after-free BUG below:

  BUG: KASAN: slab-use-after-free in __pwq_activate_work+0x1ff/0x250
  Read of size 8 at addr ffff88811f9cf800 by task kworker/u16:1/147091

  CPU: 2 UID: 0 PID: 147091 Comm: kworker/u16:1 Not tainted 6.15.0-rc2+ #27 PREEMPT(voluntary)
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014
  Workqueue:  0x0 (iw_cm_wq)
  Call Trace:
   <TASK>
   dump_stack_lvl+0x6a/0x90
   print_report+0x174/0x554
   ? __virt_addr_valid+0x208/0x430
   ? __pwq_activate_work+0x1ff/0x250
   kasan_report+0xae/0x170
   ? __pwq_activate_work+0x1ff/0x250
   __pwq_activate_work+0x1ff/0x250
   pwq_dec_nr_in_flight+0x8c5/0xfb0
   process_one_work+0xc11/0x1460
   ? __pfx_process_one_work+0x10/0x10
   ? assign_work+0x16c/0x240
   worker_thread+0x5ef/0xfd0
   ? __pfx_worker_thread+0x10/0x10
   kthread+0x3b0/0x770
   ? __pfx_kthread+0x10/0x10
   ? rcu_is_watching+0x11/0xb0
   ? _raw_spin_unlock_irq+0x24/0x50
   ? rcu_is_watching+0x11/0xb0
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x30/0x70
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>

  Allocated by task 147416:
   kasan_save_stack+0x2c/0x50
   kasan_save_track+0x10/0x30
   __kasan_kmalloc+0xa6/0xb0
   alloc_work_entries+0xa9/0x260 [iw_cm]
   iw_cm_connect+0x23/0x4a0 [iw_cm]
   rdma_connect_locked+0xbfd/0x1920 [rdma_cm]
   nvme_rdma_cm_handler+0x8e5/0x1b60 [nvme_rdma]
   cma_cm_event_handler+0xae/0x320 [rdma_cm]
   cma_work_handler+0x106/0x1b0 [rdma_cm]
   process_one_work+0x84f/0x1460
   worker_thread+0x5ef/0xfd0
   kthread+0x3b0/0x770
   ret_from_fork+0x30/0x70
   ret_from_fork_asm+0x1a/0x30

  Freed by task 147091:
   kasan_save_stack+0x2c/0x50
   kasan_save_track+0x10/0x30
   kasan_save_free_info+0x37/0x60
   __kasan_slab_free+0x4b/0x70
   kfree+0x13a/0x4b0
   dealloc_work_entries+0x125/0x1f0 [iw_cm]
   iwcm_deref_id+0x6f/0xa0 [iw_cm]
   cm_work_handler+0x136/0x1ba0 [iw_cm]
   process_one_work+0x84f/0x1460
   worker_thread+0x5ef/0xfd0
   kthread+0x3b0/0x770
   ret_from_fork+0x30/0x70
   ret_from_fork_asm+0x1a/0x30

  Last potentially related work creation:
   kasan_save_stack+0x2c/0x50
   kasan_record_aux_stack+0xa3/0xb0
   __queue_work+0x2ff/0x1390
   queue_work_on+0x67/0xc0
   cm_event_handler+0x46a/0x820 [iw_cm]
   siw_cm_upcall+0x330/0x650 [siw]
   siw_cm_work_handler+0x6b9/0x2b20 [siw]
   process_one_work+0x84f/0x1460
   worker_thread+0x5ef/0xfd0
   kthread+0x3b0/0x770
   ret_from_fork+0x30/0x70
   ret_from_fork_asm+0x1a/0x30

This BUG is reproducible by repeating the blktests test case nvme/061
for the rdma transport and the siw driver.

To avoid the use-after-free of cm_id_private work objects, ensure that
the last reference to the cm_id is decremented not in the event handler
works, but in the cm_id destruction context. For that purpose, mo
---truncated---

Statement: A use-after-free occurs when a cm_id's last reference is released from within a work item that still depends on it, resulting in a crash in __pwq_activate_work(). This race condition was reproducible via RDMA/siw transport using repeated execution of blktests nvme/061, demonstrating that deallocation of work entries must not occur from within the active work context. The CVSS Privileges Required (PR:L) rating reflects that RDMA stack access is needed, but not full root privileges, to trigger this memory corruption issue. The vulnerability does not lead to information leakage or data corruption, but results in a use-after-free crash within the kernel's RDMA workqueue processing. Therefore, for the CVSS only availability is impacted and Integrity/Confidentiality are Low (potentially impacted). As the bug causes a kernel panic or crash when triggered, the impact is rated as High on Availability.

Affected upstream versions: 4.8
Fixed upstream versions: 0, 5.10.240, 5.15.186, 5.4.296, 6.1.142, 6.12.35, 6.15.4, 6.16, 6.6.95
Upstream repository: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
Upstream fix commit: 013dcdf6f03bcedbaf1669e3db71c34a197715b2