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Message-ID: <2025112735-pedicure-nag-558b@gregkh>
Date: Thu, 27 Nov 2025 16:21:15 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Gui-Dong Han <hanguidong02@...il.com>
Cc: rafael@...nel.org, dakr@...nel.org, linux-kernel@...r.kernel.org,
baijiaju1990@...il.com, Qiu-ji Chen <chenqiuji666@...il.com>
Subject: Re: [PATCH v2] driver core: fix use-after-free of driver_override
via driver_match_device()
On Thu, Nov 27, 2025 at 11:00:16PM +0800, Gui-Dong Han wrote:
> On Thu, Nov 27, 2025 at 5:16 PM Greg KH <gregkh@...uxfoundation.org> wrote:
> >
> > On Thu, Nov 27, 2025 at 12:00:11AM +0800, Gui-Dong Han wrote:
> > > driver_set_override() modifies and frees dev->driver_override while
> > > holding device_lock(dev). However, driver_match_device() reads
> > > dev->driver_override when calling bus match functions.
> > >
> > > 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 allows a concurrent
> > > driver_set_override() to free the string while driver_match_device() is
> > > using it, leading to a use-after-free (UAF).
> > >
> > > This issue affects at least 11 bus types (including PCI, AMBA, Platform)
> > > that rely on driver_override for matching.
> > >
> > > Fix this by holding device_lock(dev) around the driver_match_device() calls
> > > in bind_store() and __driver_attach(). This ensures all access to
> > > dev->driver_override via driver_match_device() is protected by the device
> > > lock. Also add a lock assertion to driver_match_device() to prevent future
> > > locking regressions.
> > >
> > > Tested with the PoCs from Bugzilla that trigger this UAF. 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>
> > > ---
> > > 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).
> > > I chose to fix this in the driver core for the following reasons:
> > > 1. Both racing functions are part of the driver core.
> > > 2. Fixing this per-driver/per-bus is tedious and would require careful
> > > ad-hoc locking that does not align with the existing device_lock(dev).
> > > 3. We cannot simply add device_lock(dev) inside bus match functions because
> > > one call path (__device_attach_driver) already holds this lock. Adding the
> > > lock inside the match callback would cause a deadlock on that path.
> > > ---
> > > drivers/base/base.h | 2 ++
> > > drivers/base/bus.c | 17 ++++++++++++-----
> > > drivers/base/dd.c | 3 +++
> > > 3 files changed, 17 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/base/base.h b/drivers/base/base.h
> > > index 86fa7fbb3548..011e910a53f8 100644
> > > --- a/drivers/base/base.h
> > > +++ b/drivers/base/base.h
> > > @@ -166,6 +166,8 @@ 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)
> > > {
> > > + /* Protects against driver_set_override() races */
> > > + device_lock_assert(dev);
> > > return drv->bus->match ? drv->bus->match(dev, drv) : 1;
> >
> > A new line after the assert?
> >
> > And thanks for adding the comment, but:
> >
> > > }
> > >
> > > diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> > > index 5e75e1bce551..9e62d6009058 100644
> > > --- a/drivers/base/bus.c
> > > +++ b/drivers/base/bus.c
> > > @@ -261,13 +261,20 @@ 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) {
> > > + /* Protects against driver_set_override() races */
> >
> > This comment isn't needed anymore.
> >
> > > + 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 13ab98e033ea..db60b4500136 100644
> > > --- a/drivers/base/dd.c
> > > +++ b/drivers/base/dd.c
> > > @@ -1170,7 +1170,10 @@ static int __driver_attach(struct device *dev, void *data)
> > > * is an error.
> > > */
> > >
> > > + /* Protects against driver_set_override() races */
> >
> > Nor is this one.
> >
> > Also, I looked again, and why are you not grabbing the lock in the
> > bind_store() sysfs call? driver_match_device() is only called in 3
> > places, 2 now have the lock held, and one does not. This feels wrong.
>
> Actually, the change in drivers/base/bus.c is exactly for the
> bind_store() path. So all 3 call sites are covered and locked with
> this patch.
Ugh, nevermind, your patch changes bind_store() I missed that, my fault
:(
> I have verified this with the PoC for bind_store(), and the new
> lockdep assertion does not trigger any warnings, confirming the lock
> is properly held.
Makes sense, thanks!
I'll queue up your patch after 6.19-rc1 is out, thanks!
greg k-h
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