Re: [PATCH v3] mmc: vub300: fix use-after-free on probe failure

[Johan Hovold]

On Wed, Jun 10, 2026 at 11:49:03AM +0800, Guangshuo Li wrote:
> The vub300 driver lifetime-manages its controller state using
> vub300->kref, with vub300_delete() freeing the mmc host when the last
> reference is dropped. The probe error path after the inactivity timer has
> been armed still bypasses that lifetime rule, however, and falls through
> to mmc_free_host() directly if mmc_add_host() fails.
> 
> The race window is between arming the inactivity timer and reaching the
> probe error unwind after mmc_add_host() fails:
> 
>         probe thread                     timer/workqueue
>         ------------                     ---------------
>         kref_init(&vub300->kref)         ref = 1
>         kref_get(&vub300->kref)          ref = 2, timer ref
>         add_timer(inactivity_timer)      fires after one second
>         |
>         |   race window
>         |<---------------------------------------------------->
>         |
>         mmc_add_host(mmc)
>                                          inactivity timer fires
>                                          vub300_queue_dead_work()
>                                            kref_get()          ref = 3
>                                            queue_work(deadwork)
>         mmc_add_host() fails
>         timer_delete_sync()
>         mmc_free_host(mmc)
>           frees vub300
>                                          deadwork runs
>                                            use-after-free
> 
> The inactivity timeout is one second, so this would require
> mmc_add_host() to both fail and take more than one second to do so. This
> is unlikely to happen in practice, but the error path is still wrong.
> 
> timer_delete_sync() only waits for the timer callback itself. It does
> not flush deadwork that the callback may already have queued. As a
> result, queued deadwork can still hold a kref while the probe error path
> directly frees the backing mmc host, including the vub300 storage.
> 
> Fix this by using the same lifetime mechanism as disconnect. Clear
> vub300->interface so that the timer callback and any queued deadwork
> return early and drop their references, then drop the initial probe
> reference and return without falling through to err_free_host.
> 
> Fixes: 8f4d20a71022 ("mmc: vub300: fix use-after-free on disconnect")

You are using the wrong Fixes tag here again. This should be

Fixes: 0613ad2401f8 ("mmc: vub300: fix return value check of mmc_add_host()")

unless you consider this bug to have been there since the driver was
added.

> Signed-off-by: Guangshuo Li <lgs201920130244@xxxxxxxxx>
> ---
> v3:
>   - Use the disconnect-style teardown by clearing vub300->interface.
>   - Drop only the initial probe reference and let timer/deadwork drop their
>     own references.
>   - Mention the one-second inactivity timeout in the commit message.
> 
> v2:
>   - Rebase on current mainline.
>   - Correct the Fixes tag.
>   - Add blank lines around the early return.
>   - Reword the code comment.

This looks good to me now otherwise, so with the above fixed:

Reviewed-by: Johan Hovold <johan@xxxxxxxxxx>

Johan