CVE-2026-90172 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: smbdirect: destroy QP before mem pools on accept failure
On the rdma_accept_failed error path of smbdirect_accept_connect_request(), the receive io posted just above is owned by the QP (recv_io is set to NULL after a successful post). The error path fell through to smbdirect_connection_destroy_mem_pools() before smbdirect_connection_destroy_qp(), so the mem pools and the recv_io slab cache were destroyed while that recv_io was still outstanding on the QP.
The drain in smbdirect_connection_destroy_qp() (ib_drain_qp()) is what runs the recv completion that returns the recv_io to the free list, so destroying the pools first leaves the object outstanding at kmem_cache_destroy() time ("Slab cache still has objects") and later frees it into an already-destroyed mempool (mempool_free_bulk NULL-pointer dereference).
Give rdma_accept_failed its own teardown that drains the QP first, then destroys the mem pools, and returns. The remaining labels (post_recv_io_failed onward) run before the recv_io was ever posted, so they keep the mem-pools-then-qp order.
The outstanding recv_io at kmem_cache_destroy() time:
[ 3487.344647] =============================================================================
[ 3487.349942] BUG smbdirect_recv_io_cache_ffff88811ba99000 (Not tainted): Objects remaining on __kmem_cache_shutdown()
[ 3487.356078] -----------------------------------------------------------------------------
[ 3487.356078]
[ 3487.356738] Object 0xffff8881511c3440 @offset=13376
[ 3487.358464] Allocated in mempool_alloc_noprof+0x18c/0x290 age=1194 cpu=6 pid=22254
[ 3487.361197] mempool_alloc_noprof+0x18c/0x290
[ 3487.361542] smbdirect_connection_create_mem_pools+0x405/0x780
[ 3487.361972] smbdirect_accept_connect_request+0x5a8/0x1b80
[ 3487.362359] smbdirect_listen_rdma_event_handler+0x1579/0x1b90
[ 3487.362779] cma_cm_event_handler+0x9c/0x230
[ 3487.363096] cma_ib_req_handler+0x2682/0x45d0
[ 3487.363414] cm_process_work+0x56/0x3d0
[ 3487.363676] cm_work_handler+0x8a0e/0xd000
[ 3487.367496] process_scheduled_works+0xa07/0x13a0
[ 3487.367859] worker_thread+0x7c9/0xc80
[ 3487.368148] kthread+0x341/0x430
[ 3487.368407] ret_from_fork+0x3a8/0x7a0
[ 3487.368704] ret_from_fork_asm+0x1a/0x30
[ 3487.370307] Slab 0xffffea0005447000 objects=19 used=1 fp=0xffff8881511c0040 flags=0x100000000000240(workingset|head|node=0|zone=2)
[ 3487.372840] ------------[ cut here ]------------
[ 3487.373195] WARNING: mm/slub.c:1244 at __slab_err+0x1a/0x30, CPU#6: kworker/6:84/22254
[ 3487.373759] Modules linked in:
[ 3487.373993] CPU: 6 UID: 0 PID: 22254 Comm: kworker/6:84 Tainted: G B 7.1.0-next-20260623+ #88 PREEMPT(lazy)
[ 3487.374778] Tainted: [B]=BAD_PAGE
[ 3487.377830] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014
[ 3487.378515] Workqueue: ib_cm cm_work_handler
[ 3487.378820] RIP: 0010:__slab_err+0x1a/0x30
[ 3487.379129] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 e8 36 00 00 00 bf 05 00 00 00 be 01 00 00 00 e8 f7 75 45 00 90 <0f> 0b 90 c3 cc cc cc cc cc 66 66 66 66 2e 0f 1f 84 00 00 00 00 00
[ 3487.383255] RSP: 0018:ffff888220fc7050 EFLAGS: 00010093
[ 3487.383643] RAX: ffffffff8168e60a RBX: ffff88810955e640 RCX: ffff88821c381d80
[ 3487.384158] RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff870fa080
[ 3487.384662] RBP: ffff888220fc7068 R08: ffffffff870fa087 R09: 1ffffffff0e1f410
[ 3487.385192] R10: dffffc0000000000 R11: fffffbfff0e1f411 R12: ffffea0005447210
[ 3487.385674] R13: ffffea0005447000 R14: ffff888220fc7068 R15: ffff88812a8ab300
[ 3487.388932] FS: 0000000000000000(0000) GS:ffff888427e76000(0000) knlGS:0000000000000000
[ 3487.389529] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3487.389934] CR2: 00007ffcf2d84fd8 CR3: 0000000111d64006 CR4: 0000000000f72ef0
[ 3487.390440] PKRU: 55555554
[ 3487.390641] Call Trace:
[ 3487.390826] <TASK>
[ 3
---truncated---
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel involves a resource management flaw within the SMB Direct (SMBD) implementation, specifically affecting the RDMA Accept connection request handling logic. This issue manifests as an incorrect teardown sequence during error conditions where an RDMA accept operation fails. The core technical deficiency lies in the order of operations performed when cleaning up resources after a failed connection attempt. In the function smbdirect_accept_connect_request(), if the rdma_accept call encounters an error, control flow is directed to an error handling path that proceeds directly to destroying memory pools via smbdirect_connection_destroy_mem_pools(). This occurs before the Queue Pair (QP) associated with the RDMA connection is destroyed using smbdirect_connection_destroy_qp().
The operational impact of this sequencing error stems from the lifecycle management of Receive I/O buffers. When a receive operation is posted to an RDMA device, the buffer object becomes owned by the Queue Pair until it completes or is explicitly cancelled. In the context of the failed accept path, a receive I/O structure has already been allocated and posted to the QP. The mechanism that returns this object to its free list is the completion handler triggered when the QP is drained during destruction. By destroying the memory pools before draining the QP, the kernel frees the slab cache containing these buffer objects while they are still referenced as outstanding operations on the hardware queue. This results in a use-after-free scenario where subsequent attempts to access or free these buffers interact with already-deallocated memory structures.
This flaw leads to severe stability issues within the operating system environment hosting SMB Direct services. The immediate symptom is typically detected by the kernel slab allocator, which reports that objects remain on the cache during shutdown of the kmem_cache structure. This warning indicates a violation of memory management integrity rules designed to prevent leaks and corruption. More critically, if execution continues past this point, the system may attempt to free these orphaned buffers back into their original mempool using functions like mempool_free_bulk. Since the underlying pool has already been destroyed, this action triggers a NULL-pointer dereference or similar critical memory fault, leading to kernel panics and service interruptions for any applications relying on high-performance SMB over RDMA connectivity.
From a classification perspective, this vulnerability aligns with CWE-416, Use After Free, as the code attempts to utilize resources that have been deallocated due to improper ordering of cleanup routines. It also relates to CWE-755: Improper Handling of Exceptional Conditions, specifically regarding failure paths in resource management logic. In terms of adversary behavior and defensive mapping, this type of internal kernel instability can be leveraged for Denial of Service attacks against networked systems running vulnerable kernels. While not directly exploitable for arbitrary code execution without further exploitation steps involving the specific memory state corruption, it represents a significant reliability risk that attackers could trigger remotely by inducing connection failures in SMB Direct environments.
Mitigation strategies primarily involve applying vendor-provided kernel patches that correct the teardown sequence to ensure QP draining occurs before memory pool destruction. Administrators should monitor system logs for slab cache warnings or kernel panics associated with smbdirect components. For systems where RDMA-based file sharing is not required, disabling the SMB Direct module reduces the attack surface and eliminates exposure to this specific flaw until updates are deployed. Regular patching of the Linux kernel base ensures that these resource management corrections are applied across all affected versions, maintaining system stability in high-throughput network environments.