CVE-2026-80787 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
nvmet: pci-epf: fix use-after-free in nvmet_pci_epf_exec_iod_work()
nvmet_pci_epf_exec_iod_work() submits an I/O command with req->execute() and then waits for the command to complete and transfers the data back to the host. This wait is not needed for commands that do not transfer data from the device to the host. To decide whether that wait is needed, it reads iod->data_len and iod->dma_dir after calling req->execute().
However, once req->execute() is called, the command may complete asynchronously on another CPU. For commands that do not require a device-to-host data transfer, nvmet_pci_epf_queue_response() calls nvmet_pci_epf_complete_iod() directly, which can free the iod before it reads iod->data_len and iod->dma_dir, resulting in the KFENCE use-after- free:
BUG: KFENCE: use-after-free read in nvmet_pci_epf_exec_iod_work+0x288/0x798 [nvmet_pci_epf]
Use-after-free read at 0x00000000fdfa6d03 (in kfence-#63): nvmet_pci_epf_exec_iod_work+0x288/0x798 [nvmet_pci_epf]
process_one_work+0x15c/0x4f0 worker_thread+0x18c/0x30c kthread+0x130/0x140 ret_from_fork+0x10/0x20
kfence-#63: 0x00000000e3de0e71-0x00000000c938ad62, size=712, cache=kmalloc-1k
allocated by task 10 on cpu 0 at 73.995480s (0.005122s ago): mempool_kmalloc+0x1c/0x28 mempool_alloc_noprof+0x40/0x9c nvmet_pci_epf_poll_sqs_work+0xd4/0x344 [nvmet_pci_epf]
process_one_work+0x15c/0x4f0 worker_thread+0x18c/0x30c kthread+0x130/0x140 ret_from_fork+0x10/0x20
freed by task 131 on cpu 3 at 73.995521s (0.008385s ago): mempool_kfree+0x10/0x20 mempool_free+0x44/0x64 nvmet_pci_epf_free_iod+0x88/0x98 [nvmet_pci_epf]
nvmet_pci_epf_cq_work+0xfc/0x280 [nvmet_pci_epf]
process_one_work+0x15c/0x4f0 worker_thread+0x18c/0x30c kthread+0x130/0x140 ret_from_fork+0x10/0x20
Fix this by referring to iod->data_len and iod->dma_dir before calling req->execute(). The remaining iod accesses such as iod->status are only reached on the device-to-host read path. In this case, nvmet_pci_epf_queue_response() signals iod->done instead of freeing the iod, so the iod stays valid.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel vulnerability identified in the NVMe over Fabrics target PCI endpoint function driver involves a critical use-after-free condition within the work handler responsible for executing I/O commands. This flaw resides specifically in the nvmet_pci_epf_exec_iod_work function, which manages the lifecycle of Input/Output descriptors during data transfer operations between the host and the device. The core issue stems from a race condition inherent to asynchronous command processing where memory management decisions are made after an operation has potentially already completed on a different processor core.
The technical flaw arises because the code attempts to determine whether a wait is necessary for command completion by reading iod->data_len and iod->dma_dir fields immediately after invoking req->execute(). This sequence assumes that the Input/Output descriptor remains valid during this check. However, when an I/O command does not require data transfer from the device back to the host, the execution path diverges. In such cases, nvmet_pci_epf_queue_response() directly calls nvmet_pci_epf_complete_iod(), which proceeds to free the iod memory structure immediately upon completion. Since req->execute() can trigger asynchronous completion on another CPU core, there is a window where one thread frees the descriptor while another thread in nvmet_pci_epf_exec_iod_work attempts to read from it. This results in a use-after-free error detected by KFENCE, indicating that the kernel accessed memory after it had been returned to the system allocator for reuse.
The operational impact of this vulnerability is significant as it can lead to unpredictable system behavior including kernel panics, data corruption, or potential privilege escalation if an attacker can manipulate timing conditions to exploit the freed memory region. The race condition allows a local user with access to NVMe over Fabrics endpoints to trigger the faulty code path by submitting specific I/O commands that do not involve device-to-host transfers. By carefully crafting requests and potentially leveraging high-concurrency environments, an adversary might influence which CPU core handles completion versus execution, thereby increasing the likelihood of hitting the race window where the descriptor is accessed after being freed.
This vulnerability maps to CWE-416 Use After Free in common weakness enumeration standards, highlighting the improper handling of memory deallocation relative to subsequent access operations. From a threat modeling perspective aligned with MITRE ATT&CK techniques, this flaw could be leveraged for Denial of Service against critical storage infrastructure or potentially as part of a broader exploitation chain targeting kernel integrity. The specific mechanism involves exploiting asynchronous execution paths where synchronization primitives are insufficiently applied around memory lifecycle management decisions.
The resolution implemented in the Linux kernel addresses this issue by reordering operations within nvmet_pci_epf_exec_iod_work to read iod->data_len and iod->dma_dir before calling req->execute(). This ensures that all necessary metadata is captured while the descriptor is still guaranteed to be valid, regardless of how quickly the hardware or driver completes the command. For cases where data transfer from device to host occurs, nvmet_pci_epf_queue_response() signals iod->done instead of freeing the iod immediately, ensuring the structure remains accessible for subsequent status checks and cleanup procedures. This change eliminates the race condition by decoupling metadata inspection from asynchronous execution triggers.
To mitigate this vulnerability in deployed systems, administrators should apply the latest kernel updates that include the fix for nvmet_pci_epf_exec_iod_work use-after-free. Organizations relying on NVMe over Fabrics configurations must ensure their firmware and driver stacks are up to date to prevent exploitation of this race condition. Additionally, enabling KFENCE or similar memory error detection mechanisms in development environments can help identify such timing-related bugs earlier in the software lifecycle before they reach production deployments. Regular auditing of asynchronous code paths for proper synchronization is recommended as a best practice to maintain kernel stability and security integrity.