Description

In the Linux kernel, the following vulnerability has been resolved: IB/isert: wait for deferred control PDU completions before releasing the connection isert_send_done() hands ISTATE_SEND_TASKMGTRSP, ISTATE_SEND_REJECT and ISTATE_SEND_TEXTRSP completions off to isert_comp_wq and returns. The work item then runs isert_completion_put() -> isert_put_cmd(), which reads isert_conn->conn and takes conn->cmd_lock. Nothing orders that work item against teardown. isert_wait_conn() queues isert_release_work, which frees isert_conn, and iscsit_close_connection() frees the iscsit_conn right after it returns, so the queued work can run against freed memory. Count the deferred control PDU completions per connection and let isert_wait_conn() wait for them before the release work is queued. ISTATE_SEND_LOGOUTRSP is deliberately not counted: that branch runs iscsit_logout_post_handler(), which ends up waiting for conn->conn_wait_comp, and that completion is only sent by iscsit_close_connection() after it has called iscsit_wait_conn(). Waiting for it here would deadlock. Its wait stays the existing isert_wait4logout(). The splat below is from a kernel with tracing printk()s and an msleep(200) injected into isert_do_control_comp() to widen the window: BUG: KASAN: slab-use-after-free in isert_put_cmd+0x53d/0x620 Read of size 8 at addr ffff8881054f1038 by task kworker/u17:1/182 CPU: 0 UID: 0 PID: 182 Comm: kworker/u17:1 Tainted: G B 7.2.0-rc5-TWIDE-gb8babf08acc7 #1 PREEMPT(lazy) Tainted: [B]=BAD_PAGE Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: isert_comp_wq isert_do_control_comp Call Trace: <TASK> dump_stack_lvl+0x53/0x70 print_report+0xd0/0x630 ? __pfx__raw_spin_lock_irqsave+0x10/0x10 ? _raw_spin_unlock_irqrestore+0x3e/0x70 ? isert_put_cmd+0x53d/0x620 kasan_report+0xce/0x100 ? isert_put_cmd+0x53d/0x620 isert_put_cmd+0x53d/0x620 ? isert_completion_put+0x305/0x330 ? isert_do_control_comp+0x2ef/0x310 process_one_work+0x633/0x1030 ? assign_work+0x11d/0x370 worker_thread+0x45b/0xd10 ? __pfx_worker_thread+0x10/0x10 ? __pfx_worker_thread+0x10/0x10 kthread+0x2c6/0x3b0 ? recalc_sigpending+0x15c/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x36e/0x5a0 ? __pfx_ret_from_fork+0x10/0x10 ? __switch_to+0x572/0xdd0 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Allocated by task 48: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0x8f/0xa0 __kmalloc_cache_noprof+0x158/0x370 isert_cma_handler+0x1e3/0x2ae0 cma_cm_event_handler+0x3e/0x240 cma_ib_req_handler+0x17d9/0x4490 cm_process_work+0x41/0x330 cm_work_handler+0x5727/0xc160 process_one_work+0x633/0x1030 worker_thread+0x45b/0xd10 kthread+0x2c6/0x3b0 ret_from_fork+0x36e/0x5a0 ret_from_fork_asm+0x1a/0x30 Freed by task 184: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x43/0x70 kfree+0x121/0x380 iscsit_close_connection+0x7cf/0x1e60 iscsit_take_action_for_connection_exit+0x1b6/0x360 iscsi_target_tx_thread+0x472/0x690 kthread+0x2c6/0x3b0 ret_from_fork+0x36e/0x5a0 ret_from_fork_asm+0x1a/0x30

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.1",
  "pubDate": "2026-10-06T09:18:29.293Z",
  "pubdate": "2026-10-06T09:18:29.293Z",
  "executiveSummary": "A use-after-free vulnerability exists in the Linux kernel's iSER (iSCSI Extensions for RDMA) target module, specifically within the isert connection handling logic.\nThe vulnerability stems from a race condition occurring during connection teardown, where deferred control PDU completions are processed after the associated connection object has been freed.\nSuccessful exploitation allows for memory corruption or arbitrary code execution, resulting in potential system instability, kernel panics (denial of service), or unauthorized memory access.\nThe vulnerability affects systems utilizing the IB/isert driver. Attackers can trigger this condition by manipulating connection states during shutdown sequences.\nAuthentication requirements and exact exploitation complexity depend on the local network environment, but the vulnerability inherently allows for a kernel-mode use-after-free scenario when concurrent teardown processes proceed without synchronization.",
  "technicalDetails": "The vulnerability is a classic use-after-free condition within the Linux kernel's IB/isert implementation, specifically involving the asynchronous handling of deferred control PDU completions. The component responsible for this behavior is the iSER target driver, which manages RDMA-based iSCSI connections.\nThe root cause is a lack of synchronization between the asynchronous work queue (isert_comp_wq) and the connection teardown process. In the current implementation, isert_send_done() offloads specific completions—namely ISTATE_SEND_TASKMGTRSP, ISTATE_SEND_REJECT, and ISTATE_SEND_TEXTRSP—to the isert_comp_wq. These work items eventually invoke isert_put_cmd(), which accesses the isert_conn->conn structure and attempts to acquire the conn->cmd_lock.\nDuring connection teardown, isert_wait_conn() triggers the queued isert_release_work task, which deallocates the isert_conn object. Simultaneously, the iscsit_close_connection() function frees the underlying iscsit_conn structure upon completion. Because there is no mechanism to ensure that all pending work items in isert_comp_wq have completed their execution and released references to these connection structures before the deallocation occurs, a race condition exists.\nAn attacker can exploit this by forcing a connection shutdown while deferred PDU completions are still pending in the work queue. If the teardown proceeds faster than the worker thread, the worker thread will eventually attempt to access members of the now-freed isert_conn or iscsit_conn memory regions. The KASAN report provided confirms a slab-use-after-free vulnerability during a read operation at offset 8, originating from the isert_put_cmd function.\nThe attack flow involves: 1) Initiating a connection that results in pending deferred control PDUs; 2) Triggering an abrupt connection teardown; 3) Exploiting the window of time between the destruction of connection objects and the execution of the lingering work queue items. Once the memory is freed by the kernel, the worker thread's subsequent read/write access to that memory leads to a kernel panic. While ISTATE_SEND_LOGOUTRSP is explicitly excluded from this race condition due to existing wait logic for Logout responses, the other control PDUs remain exposed to this synchronization flaw."
}