Re: [PATCH] remoteproc: core: Do not put the device when device_add() fails

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Thu, Oct 29, 2026 at 09:00:37PM +0800, Yuqiang Sun wrote:
> When device_add() fails, rproc_add() calls put_device() and then
> removes the character device.  The reference it drops is the one
> rproc_alloc() took with device_initialize(), which belongs to the
> caller: after a failed rproc_add(), every driver frees the rproc,
> either with rproc_free() or through devm_rproc_alloc(), and both drop
> that reference again.
> 
> So the rproc is freed inside rproc_add(): by the put_device() itself,
> or, with CONFIG_REMOTEPROC_CDEV, by the cdev_del() that follows, when
> the character device drops its reference on the parent device.  The
> caller then uses the freed rproc and puts it a second time.
> 
> With one allocation failure injected into device_add() (failslab
> restricted to rproc_add) while st_fdma probes, KASAN reports:
> 
>   BUG: KASAN: slab-use-after-free in slim_clk_disable+0x38/0xf4 [st_slim_rproc]
>   Read of size 8 by task insmod/69
>   Call trace:
>    slim_clk_disable
>    st_slim_rproc_alloc
>    st_fdma_probe
>   Freed by task 69:
>    kfree
>    rproc_type_release
>    device_release
>    kobject_put
>    cdev_default_release
>    kobject_put
>    cdev_del
>    rproc_char_device_remove
>    rproc_add
>    st_slim_rproc_alloc
> 
> followed by use-after-free reports in kobject_put() and
> refcount_warn_saturate() from the rproc_free() in
> st_slim_rproc_alloc().
> 
> Remove the put_device(): the caller's rproc_free() drops the reference
> and releases the rproc, as it does for the other failures in
> rproc_add().
> 
> The problem was found with kbound, a static analysis prototype that
> checks whether callers rely on an object after a callee returns a value
> for which the callee may have released it, on v7.2.12; it is present
> in rproc-next.
> 
> Build-tested with x86_64 and arm64 allmodconfig (W=1, sparse): no new
> warnings.  Run-tested on QEMU's arm64 virt machine (TCG) with KASAN,
> using a device tree node for an ST FDMA with a SLIM core, so that
> st_fdma_probe() reaches rproc_add() without the hardware (no clocks,
> MMIO windows only mapped), and failing each allocation in rproc_add()
> in turn with failslab: before this patch every failure in device_add()
> (9 of 9) gives the reports above; with it nothing is reported, and the
> rproc is released once, by rproc_free().  Not tested on remoteproc
> hardware.
> 
> Fixes: 7dbdb8bd7c02 ("remoteproc: core: Cleanup device in case of failure")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-opus-5-5 kbound
> Signed-off-by: Yuqiang Sun <izaiahsun@gmail.com>
> ---
>  drivers/remoteproc/remoteproc_core.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> index b88bf179507d..e4f44a3c8b4d 100644
> --- a/drivers/remoteproc/remoteproc_core.c
> +++ b/drivers/remoteproc/remoteproc_core.c
> @@ -2309,10 +2309,8 @@ int rproc_add(struct rproc *rproc)
>  		return ret;
>  
>  	ret = device_add(dev);
> -	if (ret < 0) {
> -		put_device(dev);

The documentation for device_add() is clear, and looking at the implementation
of device_add(), I understand why put_device() needs to be called here.

Unfortunately I do not have the time to read through and digest what Claude has
generated in the changelog.

Thanks,
Mathieu


> +	if (ret < 0)
>  		goto rproc_remove_cdev;
> -	}
>  
>  	dev_info(dev, "%s is available\n", rproc->name);
>  
> 
> base-commit: 82d0bbd67c42a44f0e18b0b7b0da0f3ace0c9527
> -- 
> 2.53.0
>