Re: [PATCH v2] nvmet: pci-epf: fix use-after-free in nvmet_pci_epf_exec_iod_work()

On 7/14/26 13:00, Shin'ichiro Kawasaki wrote:
> 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.
> 
> Fixes: 0faa0fe6f90e ("nvmet: New NVMe PCI endpoint function target driver")
> Cc: [email protected]
> Signed-off-by: Shin'ichiro Kawasaki <[email protected]>

Looks good to me.

Reviewed-by: Damien Le Moal <[email protected]>


-- 
Damien Le Moal
Western Digital Research