Re: [PATCH] dmaengine: idxd: Fix use-after-free in idxd_remove

[Frank Li]

On Fri, Sep 11, 2026 at 02:55:47PM +0800, Ziyou Wang (Lenovo) wrote:
> [You don't often get email from ziyou.dev@xxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> When unbinding the idxd driver, the following call trace is observed:
>
>   general protection fault, probably for non-canonical address 0x18fc1d6937256657
>   CPU: 117 UID: 0 PID: 3396 Comm: python3 Tainted: G E 7.2.0-rc5-latest+ #11 PREEMPT(lazy)
>   Hardware name: Lenovo WenTian WR5220 G5, BIOS speb50m-2.54
>   RIP: 0010:__refill_objects_node+0x2da/0x5e0
>   Call Trace:
>    <TASK>
>    refill_objects+0x1ee/0x2e0
>    __pcs_replace_empty_main+0x1e1/0x330
>    __kmalloc_noprof+0x503/0x550
>    ext4_htree_store_dirent+0x34/0x110 [ext4]
>    htree_dirblock_to_tree+0x1a9/0x2c0 [ext4]
>    ext4_htree_fill_tree+0x246/0x3d0 [ext4]
>    ext4_readdir+0x863/0x9d0 [ext4]
>    iterate_dir+0xa6/0x260
>    __x64_sys_getdents64+0x76/0x130
>    do_syscall_64+0x98/0x620
>    entry_SYSCALL_64_after_hwframe+0x76/0x7e
>    </TASK>
>
> With the KASAN-enabled kernel, the kernel reports a use-after-free bug:
>
> idxd_unregister_devices() calls device_unregister(wq), which triggers
> the wq release callback and frees wq memory via kfree(). However,
> idxd->wqs[] array still holds the freed pointer. Later, when
> device_unregister(idxd) calls idxd_device_drv_remove(), it accesses
> wq->state through idxd->wqs[], resulting in use-after-free.
>
> The same issue exists for idxd->engines[] and idxd->groups[] arrays.
>
> KASAN report:
>
>   BUG: KASAN: slab-use-after-free in idxd_device_drv_remove+0xc1/0x100 [idxd]
>   Read of size 4 at addr ff1100038d296414 by task python3/3354
>   CPU: 20 UID: 0 PID: 3354 Comm: python3 Tainted: G E 7.2.0-rc5-debug+
>   Hardware name: Lenovo WenTian WR5220 G5, BIOS speb50m-2.54
>
>   Call Trace:
>     <TASK>
>     dump_stack_lvl+0x5b/0x80
>     print_report+0x153/0x4b5
>     kasan_report+0xbc/0xf0
>     idxd_device_drv_remove+0xc1/0x100 [idxd]
>     device_release_driver_internal+0x244/0x2e0
>     bus_remove_device+0x195/0x2b0
>     device_del+0x24b/0x540
>     device_unregister+0x17/0x80
>     idxd_remove+0x3f/0x120 [idxd]
>     pci_device_remove+0x6d/0xf0
>     device_release_driver_internal+0x244/0x2e0
>     unbind_store+0xae/0xb0
>     kernfs_fop_write_iter+0x205/0x2d0
>     vfs_write+0x3a9/0x6b0
>     ksys_write+0xc7/0x160
>     do_syscall_64+0x9c/0x620
>     entry_SYSCALL_64_after_hwframe+0x76/0x7e
>     </TASK>
>
>   Allocated by task 1219:
>     kasan_save_stack+0x20/0x40
>     kasan_save_track+0x14/0x30
>     __kasan_kmalloc+0x9a/0xb0
>     __kmalloc_cache_node_noprof+0x1c6/0x470
>     idxd_pci_probe_alloc+0x103f/0x2430 [idxd]
>     local_pci_probe+0x71/0xd0
>     local_pci_probe_callback+0x20/0x40
>     process_one_work+0x389/0x6a0
>     worker_thread+0x321+0x590
>     kthread+0x1b4/0x200
>     ret_from_fork+0x3bd/0x4d0
>     ret_from_fork_asm+0x1a/0x30
>
>   Freed by task 3354:
>     kasan_save_stack+0x20/0x40
>     kasan_save_track+0x14/0x30
>     kasan_save_free_info+0x3b/0x70
>     __kasan_slab_free+0x6b/0x90
>     kfree+0x1d4/0x520
>     device_release+0x77/0x120
>     kobject_put+0xdb/0x2a0
>     idxd_unregister_devices+0x5b/0x130 [idxd]
>     idxd_remove+0x2f/0x120 [idxd]
>     pci_device_remove+0x6d/0xf0
>     device_release_driver_internal+0x244/0x2e0
>     unbind_store+0xae/0xb0
>     kernfs_fop_write_iter+0x205/0x2d0
>     vfs_write+0x3a9/0x6b0
>     ksys_write+0xc7/0x160
>     do_syscall_64+0x9c/0x620
>     entry_SYSCALL_64_after_hwframe+0x76/0x7e

Can you trim dump to make commit message short.

>
> Fix by taking refs on wq/engine/group conf_dev in idxd_unregister_devices()
> before calling device_unregister(). This prevents their memory from being
> freed until after idxd_device_drv_remove() completes. Add idxd_put_devices()
> to release the refs after all cleanup activities are done.
>
> To reproduce:
>   cd dsa-perf-micros
>   ./scripts/setup_dsa.sh -d dsa0 -w 1 -m s -e 4
>   echo "0000:00:01.0" > /sys/bus/pci/drivers/idxd/unbind

This is typical unbind driver method. So needn't this paragraph.

Frank

>
> Fixes: 47c16ac27d4c ("dmaengine: idxd: fix idxd conf_dev 'struct device' lifetime")
> Suggested-by: Adrian Huang (Lenovo) <adrianhuang0701@xxxxxxxxx>
> Signed-off-by: Ziyou Wang (Lenovo) <ziyou.dev@xxxxxxxxx>
> ---
> Added a Suggested-by tag for Adrian, as he came up with the idea for this patch.
>
>  drivers/dma/idxd/init.c  | 15 +++++++++++++++
>  drivers/dma/idxd/sysfs.c |  8 ++++++++
>  2 files changed, 23 insertions(+)
>
> diff --git a/drivers/dma/idxd/init.c b/drivers/dma/idxd/init.c
> index 4b827a329756..212efbfebacc 100644
> --- a/drivers/dma/idxd/init.c
> +++ b/drivers/dma/idxd/init.c
> @@ -1263,6 +1263,20 @@ static void idxd_shutdown(struct pci_dev *pdev)
>         flush_workqueue(idxd->wq);
>  }
>
> +static void idxd_put_devices(struct idxd_device *idxd)
> +{
> +       int i;
> +
> +       for (i = 0; i < idxd->max_wqs; i++)
> +               put_device(wq_confdev(idxd->wqs[i]));
> +
> +       for (i = 0; i < idxd->max_engines; i++)
> +               put_device(engine_confdev(idxd->engines[i]));
> +
> +       for (i = 0; i < idxd->max_groups; i++)
> +               put_device(group_confdev(idxd->groups[i]));
> +}
> +
>  static void idxd_remove(struct pci_dev *pdev)
>  {
>         struct idxd_device *idxd = pci_get_drvdata(pdev);
> @@ -1284,6 +1298,7 @@ static void idxd_remove(struct pci_dev *pdev)
>         if (device_pasid_enabled(idxd))
>                 idxd_disable_system_pasid(idxd);
>         pci_iounmap(pdev, idxd->reg_base);
> +       idxd_put_devices(idxd);
>         put_device(idxd_confdev(idxd));
>         pci_disable_device(pdev);
>  }
> diff --git a/drivers/dma/idxd/sysfs.c b/drivers/dma/idxd/sysfs.c
> index 6d251095c350..eca96a4dcecd 100644
> --- a/drivers/dma/idxd/sysfs.c
> +++ b/drivers/dma/idxd/sysfs.c
> @@ -1988,21 +1988,29 @@ void idxd_unregister_devices(struct idxd_device *idxd)
>  {
>         int i;
>
> +       /*
> +        * Take a reference count to the idxd device to prevent the
> +        * corresponding idxd context from being freed, as the driver
> +        * still needs it for the remaining cleanup operations.
> +        */
>         for (i = 0; i < idxd->max_wqs; i++) {
>                 struct idxd_wq *wq = idxd->wqs[i];
>
> +               get_device(wq_confdev(wq));
>                 device_unregister(wq_confdev(wq));
>         }
>
>         for (i = 0; i < idxd->max_engines; i++) {
>                 struct idxd_engine *engine = idxd->engines[i];
>
> +               get_device(engine_confdev(engine));
>                 device_unregister(engine_confdev(engine));
>         }
>
>         for (i = 0; i < idxd->max_groups; i++) {
>                 struct idxd_group *group = idxd->groups[i];
>
> +               get_device(group_confdev(group));
>                 device_unregister(group_confdev(group));
>         }
>  }
> --
> 2.53.0
>