linux-kernel - Re: [PATCH v2] driver core: fix use-after-free of driver_override via driver_match

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Message-ID: <CALbr=LYsp4KksV_Oydcbb09t0C9uGpV2Ow7A0A+YZSNM39FOuQ@mail.gmail.com>
Date: Tue, 13 Jan 2026 10:27:39 +0800
From: Gui-Dong Han <hanguidong02@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
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 11:21 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> 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!

Hi Greg,

Apologies for the ping, but I noticed this patch hasn't been merged
yet and I couldn't find it in the driver-core-next branch. I wanted to
check if it might have been missed.

If you plan to pick it up, please use v3 which I sent shortly after
this thread to address your feedback regarding code formatting.

v3 link: https://lore.kernel.org/all/20251127145753.13080-1-hanguidong02@gmail.com/

Sorry if I missed something on my end.

Thanks.