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Message-ID: <CALbr=Lb5HmoBFwuyCcoXnFvMjDh6zcfaw0mgT_mq80wU5L0Pww@mail.gmail.com>
Date: Wed, 14 Jan 2026 00:32:28 +0800
From: Gui-Dong Han <hanguidong02@...il.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: gregkh@...uxfoundation.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 Wed, Jan 14, 2026 at 12:03 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Tue, Jan 13, 2026 at 4:56 PM Gui-Dong Han <hanguidong02@...il.com> wrote:
> >
> > On Tue, Jan 13, 2026 at 11:20 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > >
> > > 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?
> >
> > Hi Rafael,
> >
> > The three call sites for driver_match_device() have been stable for
> > over a decade.
>
> Yes, they have, but now it's changing.
>
> > With only two sites requiring the lock, and no new
> > callers anticipated, adding a helper function seems to have limited
> > value.
>
> It would reduce code duplication. Why is this limited value?
I see. I have submitted v5 with the helper function
driver_match_device_locked() as suggested.
Thanks.
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