CVE-2026-98815 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
nvme: fix cdev lifetime
Sashiko bot reported a potential problem for the cdev lifetime in [0]
- the code there is heavily based on the NVMe code.
Currently the NS head .open and .release file_operations methods take and put a reference to the nvme_ns_head to ensure that this structure does not disappear while we open fds for that cdev.
In multipath mode, when we teardown the NS head, we call nvme_cdev_del() -> cdev_device_del() -> cdev_del(). However after cdev_del() returns, cdevs already open will remain and their fops will still be callable. As such, we can still reference the cdev after the nvme_ns_head reference count drops to 0 (and is freed).
This can be shown with an application which delays between opening the cdev and issuing the ioctl while the NS head is being torn down:
# ./ioctl_file /dev/ng1n1 & # waiting 10 seconds ....
# ./ini_nvme_teardown.sh [ 21.221718] nvme nvme1: Removing ctrl: NQN "nvme-test-target"
[ 21.274609] nvme nvme2: Removing ctrl: NQN "nvme-test-target"
# now going to issue ioctl .... [ 26.549285] ==================================================================
[ 26.550841] BUG: KASAN: slab-use-after-free in cdev_put.part.0+0x3d/0x40
[ 26.552352] Read of size 8 at addr ffff88811e7fa170 by task ioctl_file/237
[ 26.553805]
[ 26.554227] CPU: 3 UID: 0 PID: 237 Comm: ioctl_file Not tainted 7.2.0-rc1-00004-g6852a10e32d4 #921 PREEMPT(lazy)
[ 26.554236] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 26.554241] Call Trace:
[ 26.554245] <TASK>
[ 26.554248] dump_stack_lvl+0x68/0xa0
[ 26.554266] print_report+0x10d/0x5d0
[ 26.554276] ? __virt_addr_valid+0x21d/0x3f0
[ 26.554287] ? cdev_put.part.0+0x3d/0x40
[ 26.554292] kasan_report+0x96/0xd0
[ 26.554300] ? cdev_put.part.0+0x3d/0x40
[ 26.554307] cdev_put.part.0+0x3d/0x40
[ 26.554313] __fput+0x7bc/0xa70
[ 26.554322] fput_close_sync+0xd8/0x190
[ 26.554328] ? __pfx_fput_close_sync+0x10/0x10
[ 26.554337] __x64_sys_close+0x79/0xd0
[ 26.554344] do_syscall_64+0x117/0x6b0
[ 26.554351] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 26.554358] RIP: 0033:0x7f938c067727
[ 26.554364] Code: 48 89 fa 4c 89 df e8 28 ad 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5bf
[ 26.554369] RSP: 002b:00007fff49f05980 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
[ 26.554376] RAX: ffffffffffffffda RBX: 00007f938bfd7780 RCX: 00007f938c067727
[ 26.554380] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
[ 26.554383] RBP: 00007fff49f05a10 R08: 0000000000000000 R09: 0000000000000000
[ 26.554386] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[ 26.554389] R13: 00007fff49f05b40 R14: 00007f938c207000 R15: 000055c148471d78
[ 26.554397] </TASK>
[ 26.554399]
[ 26.575612] Allocated by task 100:
[ 26.575871] kasan_save_stack+0x24/0x50
[ 26.576157] kasan_save_track+0x14/0x30
[ 26.576418] __kasan_kmalloc+0x7f/0x90
[ 26.576668] __kmalloc_noprof+0x281/0x6c0
[ 26.576938] nvme_alloc_ns+0x7f7/0x3170
[ 26.577206] nvme_scan_ns+0x508/0x880
[ 26.577449] async_run_entry_fn+0x8c/0x350
[ 26.577723] process_scheduled_works+0xb6f/0x1a00
[ 26.578034] worker_thread+0x4ad/0xb40
[ 26.578283] kthread+0x34f/0x450
[ 26.578501] ret_from_fork+0x563/0x800
[ 26.578752] ret_from_fork_asm+0x1a/0x30
[ 26.579012]
[ 26.579124] Freed by task 237:
[ 26.579335] kasan_save_stack+0x24/0x50
[ 26.579596] kasan_save_track+0x14/0x30
[ 26.579855] kasan_save_free_info+0x3a/0x60
[ 26.580131] __kasan_slab_free+0x43/0x70
[ 26.580388] kfree+0x321/0x500
[ 26.580591] nvme_ns_head_chr_release+0x39/0x50
[ 26.580883] __fput+0x352/0xa70
[ 26.581095] fput_close_sync+0xd8/0x190
[ 26.581350] __x64_sys_close+0x79/0xd0
[ 26.581595] do_syscall_64+0x117/0x6b0
[ 26.581842] entry_SYSCAL
---truncated---
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel NVMe subsystem contains a critical use-after-free vulnerability related to the lifetime management of character device structures associated with namespace heads. This flaw arises from an imbalance in reference counting mechanisms during the teardown process of NVMe namespaces, particularly within multipath configurations where multiple paths may exist for a single logical unit. The core issue stems from how the kernel handles file operations when a user-space application holds an open file descriptor to an NVMe character device while the underlying hardware controller or namespace is being removed. Specifically, the nvme_ns_head structure maintains references through its .open and .release methods in the file_operations interface, intending to keep the structure alive as long as any file descriptors are active. However, during teardown sequences initiated by administrative commands such as NVMe subsystem removal, the kernel invokes cdev_del() which removes the character device from the system's global list of devices but does not immediately invalidate or block access to already open file descriptors associated with that device node.
This architectural oversight creates a race condition window where an application can successfully open a handle to /dev/ngXnY and then delay issuing any ioctls while another process triggers the teardown of the NVMe controller or namespace head. When cdev_del() executes, it signals the kernel's character device subsystem that the device is no longer available for new opens, but existing file structures remain valid in memory until they are explicitly closed by user space. If the nvme_ns_head reference count drops to zero during this interval because all other references have been released or due to teardown logic freeing the structure prematurely, the underlying memory backing the namespace head is returned to the slab allocator and potentially reused for other allocations. Consequently, if a thread that opened the device earlier attempts to perform an ioctl operation after the ns_head has been freed but before it closes its file descriptor, it will dereference a pointer to deallocated memory.
The operational impact of this vulnerability manifests as kernel crashes or undefined behavior depending on how quickly the freed memory is reallocated by other subsystems. As evidenced by Kernel Address Sanitizer (KASAN) reports, accessing fields within the nvme_ns_head structure after its release triggers slab-use-after-free errors. These errors typically result in system panics, denial of service conditions for local users with access to NVMe devices, or potentially more severe outcomes if an attacker can control the data written into the reclaimed memory region before it is accessed again. The vulnerability affects systems running affected kernel versions where NVMe multipath configurations are utilized and administrative actions such as controller removal occur concurrently with user-space interactions via character device interfaces.
From a classification perspective, this flaw aligns closely with CWE-416: Use After Free, which describes the error of using memory after it has been freed, leading to unpredictable behavior including crashes or code execution. In terms of adversarial tactics, this vulnerability could be leveraged within ATT&CK technique T1059: Command and Scripting Interpreter if an attacker can trigger specific ioctl calls that interact with kernel structures in a way that facilitates further exploitation, although the primary immediate impact is stability-related denial of service rather than direct privilege escalation. The root cause lies in insufficient synchronization between the device removal lifecycle and the file descriptor release mechanisms, failing to ensure that all active references are properly cleaned up before memory deallocation occurs.
Mitigation strategies primarily involve applying kernel patches that correct the reference counting logic within the NVMe subsystem developers have addressed this by ensuring proper lifetime management of cdev structures relative to their underlying namespace heads. System administrators should prioritize updating to patched kernel versions where these synchronization issues are resolved, preventing premature freeing of nvme_ns_head structures while file descriptors remain open. Additionally, restricting access to raw NVMe character devices like /dev/ng* to trusted processes reduces the attack surface for local users who might otherwise exploit this race condition through crafted timing attacks involving delayed ioctl operations during controller teardown events.