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

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Message-ID: <CALbr=LaozardXKTbSotc2y7z+_m40EqFZ7Jn4vO1jFyRT3bKVQ@mail.gmail.com>
Date: Wed, 26 Nov 2025 19:55:06 +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] driver core: fix use-after-free of driver_override via driver_match_device()

On Wed, Nov 26, 2025 at 7:39 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Nov 26, 2025 at 07:30:06PM +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.
> >
> > 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>
> > ---
> > 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/bus.c | 17 ++++++++++++-----
> >  drivers/base/dd.c  |  3 +++
> >  2 files changed, 15 insertions(+), 5 deletions(-)
> >
> > 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 */
> > +             device_lock(dev);
> > +             ret = driver_match_device(drv, dev);
> > +             device_unlock(dev);
>
> Why not have driver_match_device() take the lock instead?  This way
> looks like an "anti-pattern" that we will get wrong over time.

The reason I did not put the lock inside driver_match_device() is that
one of its existing callers, __device_attach_driver(), already holds
device_lock(dev). Unconditionally adding the lock inside
driver_match_device() would cause a deadlock on that path.

To address this and move the locking inside as you suggested, I would
need to modify the signature of driver_match_device() to accept a
flag, for example:
int driver_match_device(struct device_driver *drv, struct device *dev,
bool locked)

This would allow the function to conditionally acquire the lock based
on the caller's context.

Is this design acceptable? If so, I can prepare a v2 with this approach.

Thanks,
Gui-Dong Han