linux-kernel - Re: [PATCH v4] driver core: enforce device_lock for driver_match

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Message-ID: <CAJZ5v0hb=bgjN79+ODJUmfumy0r7JMS77wd1QpMOcJAN5DmRww@mail.gmail.com>
Date: Tue, 13 Jan 2026 16:20:26 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Gui-Dong Han <hanguidong02@...il.com>
Cc: gregkh@...uxfoundation.org, rafael@...nel.org, dakr@...nel.org, 
	linux-kernel@...r.kernel.org, baijiaju1990@...il.com, 
	Qiu-ji Chen <chenqiuji666@...il.com>
Subject: Re: [PATCH v4] driver core: enforce device_lock for driver_match_device()

On Tue, Jan 13, 2026 at 4:05 PM Gui-Dong Han <hanguidong02@...il.com> wrote:
>
> Currently, driver_match_device() is called from three sites. One site
> (__device_attach_driver) holds device_lock(dev), but the other two
> (bind_store and __driver_attach) do not. This inconsistency means that
> bus match() callbacks are not guaranteed to be called with the lock
> held.
>
> Fix this by holding device_lock(dev) around the driver_match_device()
> calls in bind_store() and __driver_attach(). This ensures consistent
> locking for all match() callbacks. Also add a lock assertion to
> driver_match_device() to enforce this guarantee.
>
> This consistency also fixes a known race condition. The driver_override
> implementation relies on the device_lock, so the missing lock led to the
> use-after-free (UAF) reported in Bugzilla for buses using this field.
>
> Stress testing the two newly locked paths for 24 hours with
> CONFIG_PROVE_LOCKING and CONFIG_LOCKDEP enabled showed no UAF recurrence
> and no lockdep warnings.
>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=220789
> Suggested-by: Qiu-ji Chen <chenqiuji666@...il.com>
> Signed-off-by: Gui-Dong Han <hanguidong02@...il.com>
> ---
> v4:
> * Remove the misleading comment above device_lock_assert(), and update
> subject and commit message to focus on enforcing consistent locking,
> as discussed with Danilo Krummrich.
> v3:
> * Remove redundant locking comments at call sites and add a blank line
> after the lock assertion in driver_match_device(), as suggested by Greg KH.
> v2:
> * Add device_lock_assert() in driver_match_device() to enforce locking
> requirement, as suggested by Greg KH.
> v1:
> * The Bugzilla entry contains full KASAN reports and two PoCs that reliably
> reproduce the UAF on both unlocked paths using a standard QEMU setup
> (default e1000 device at 0000:00:03.0).
> ---
>  drivers/base/base.h |  2 ++
>  drivers/base/bus.c  | 16 +++++++++++-----
>  drivers/base/dd.c   |  2 ++
>  3 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 430cbefbc97f..aa701878c6e3 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -182,6 +182,8 @@ void device_set_deferred_probe_reason(const struct device *dev, struct va_format
>  static inline int driver_match_device(const struct device_driver *drv,
>                                       struct device *dev)
>  {
> +       device_lock_assert(dev);
> +
>         return drv->bus->match ? drv->bus->match(dev, drv) : 1;
>  }
>
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 9eb7771706f0..5cbcf9f5bd6e 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -261,13 +261,19 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf,
>         const struct bus_type *bus = bus_get(drv->bus);
>         struct device *dev;
>         int err = -ENODEV;
> +       int ret;
>
>         dev = bus_find_device_by_name(bus, NULL, buf);
> -       if (dev && driver_match_device(drv, dev)) {
> -               err = device_driver_attach(drv, dev);
> -               if (!err) {
> -                       /* success */
> -                       err = count;
> +       if (dev) {
> +               device_lock(dev);
> +               ret = driver_match_device(drv, dev);
> +               device_unlock(dev);
> +               if (ret) {
> +                       err = device_driver_attach(drv, dev);
> +                       if (!err) {
> +                               /* success */
> +                               err = count;
> +                       }
>                 }
>         }
>         put_device(dev);
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 349f31bedfa1..e79c732a56e4 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -1178,7 +1178,9 @@ static int __driver_attach(struct device *dev, void *data)
>          * is an error.
>          */
>
> +       device_lock(dev);
>         ret = driver_match_device(drv, dev);
> +       device_unlock(dev);

This repeats the pattern above, so maybe add a helper function for it?

And use the device guard in there?

>         if (ret == 0) {
>                 /* no match */
>                 return 0;
> --