Re: [PATCH v1] at24: fix memory corruption race condition

Daniel Okazaki
2024-04-18T17:16:07Z

Sorry forgot to include the key being that the probes happen in
parallel so there are race conditions to the registering of the
nvmem and other drivers using it after it starts getting torn down
and memory gets freed.

On Thu, Apr 18, 2024 at 10:13 AM Daniel Okazaki <dtokazaki@google.com> wrote:
>
> nvmem devices allow for linking by name in the DTS which doesn't
> create a dependency in the probe order.
>
> What happens is driver B probe starts shortly after the eeprom
> probe and calls of_nvmem_device_get. Since a device is
> registered it starts using it; however if the eeprom isn't there
> then the read will fail and it will start tearing down the resources.
> Driver B will now access invalid memory causing a kernel panic.
>
> Daniel
>
>
> On Wed, Apr 17, 2024 at 5:23 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> >
> > On Thu, Apr 18, 2024 at 1:59 AM Bartosz Golaszewski <brgl@bgdev.pl> wrote:
> > >
> > > On Thu, Apr 18, 2024 at 1:07 AM Daniel Okazaki <dtokazaki@google.com> wrote:
> > > >
> > > > If the eeprom is not accessible, an nvmem device will be registered, the
> > > > read will fail, and the device will be torn down. If another driver
> > > > accesses the nvmem device after the teardown, it will reference
> > > > invalid memory.
> > > >
> > > > Move the failure point before registering the nvmem device.
> > > >
> > > > Signed-off-by: Daniel Okazaki <dtokazaki@google.com>
> > > > ---
> > > > drivers/misc/eeprom/at24.c | 18 +++++++++---------
> > > > 1 file changed, 9 insertions(+), 9 deletions(-)
> > > >
> > > > diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
> > > > index 572333ead5fb..4bd4f32bcdab 100644
> > > > --- a/drivers/misc/eeprom/at24.c
> > > > +++ b/drivers/misc/eeprom/at24.c
> > > > @@ -758,15 +758,6 @@ static int at24_probe(struct i2c_client *client)
> > > > }
> > > > pm_runtime_enable(dev);
> > > >
> > > > - at24->nvmem = devm_nvmem_register(dev, &nvmem_config);
> > > > - if (IS_ERR(at24->nvmem)) {
> > > > - pm_runtime_disable(dev);
> > > > - if (!pm_runtime_status_suspended(dev))
> > > > - regulator_disable(at24->vcc_reg);
> > > > - return dev_err_probe(dev, PTR_ERR(at24->nvmem),
> > > > - "failed to register nvmem\n");
> > > > - }
> > > > -
> > > > /*
> > > > * Perform a one-byte test read to verify that the chip is functional,
> > > > * unless powering on the device is to be avoided during probe (i.e.
> > > > @@ -782,6 +773,15 @@ static int at24_probe(struct i2c_client *client)
> > > > }
> > > > }
> > > >
> > > > + at24->nvmem = devm_nvmem_register(dev, &nvmem_config);
> > > > + if (IS_ERR(at24->nvmem)) {
> > > > + pm_runtime_disable(dev);
> > > > + if (!pm_runtime_status_suspended(dev))
> > > > + regulator_disable(at24->vcc_reg);
> > > > + return dev_err_probe(dev, PTR_ERR(at24->nvmem),
> > > > + "failed to register nvmem\n");
> > > > + }
> > > > +
> > > > /* If this a SPD EEPROM, probe for DDR3 thermal sensor */
> > > > if (cdata == &at24_data_spd)
> > > > at24_probe_temp_sensor(client);
> > > > --
> > > > 2.44.0.683.g7961c838ac-goog
> > > >
> > >
> > > Looks good, can you add a Fixes tag?
> > >
> > > Thanks,
> > > Bartosz
> >
> > Wait... While the patch is still correct - we shouldn't needlessly
> > create the nvmem device - why would anything crash? Looks like a
> > problem with nvmem then? How did you trigger this issue?
> >
> > Bart