Re: [PATCH] devcoredump: Remove devcoredump device if failing device is gone

[Rodrigo Vivi]

On Fri, Jan 19, 2024 at 01:13:45PM -0500, Souza, Jose wrote:
> On Wed, 2024-01-17 at 14:53 -0500, Rodrigo Vivi wrote:
> > Make dev_coredumpm a real device managed helper, that not only
> > frees the device after a scheduled delay (DEVCD_TIMEOUT), but
> > also when the failing/crashed device is gone.
> > 
> > The module remove for the drivers using devcoredump are currently
> > broken if attempted between the crash and the DEVCD_TIMEOUT, since
> > the symbolic sysfs link won't be deleted.
> > 
> > On top of that, for PCI devices, the unbind of the device will
> > call the pci .remove void function, that cannot fail. At that
> > time, our device is pretty much gone, but the read and free
> > functions are alive trough the devcoredump device and they
> > can get some NULL dereferences or use after free.
> > 
> > So, if the failing-device is gone, let's cancel the scheduled
> > work and remove devcoredump-device immediately.
> > 
> > Cc: Jose Souza <jose.souza@xxxxxxxxx>
> > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> > Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> > ---
> >  drivers/base/devcoredump.c | 29 ++++++++++++++++++++++-------
> >  1 file changed, 22 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
> > index 7e2d1f0d903a..6db7a2fd9a02 100644
> > --- a/drivers/base/devcoredump.c
> > +++ b/drivers/base/devcoredump.c
> > @@ -8,6 +8,7 @@
> >  #include <linux/module.h>
> >  #include <linux/device.h>
> >  #include <linux/devcoredump.h>
> > +#include <linux/devm-helpers.h>
> >  #include <linux/list.h>
> >  #include <linux/slab.h>
> >  #include <linux/fs.h>
> > @@ -118,19 +119,24 @@ static ssize_t devcd_data_read(struct file *filp, struct kobject *kobj,
> >  	return devcd->read(buffer, offset, count, devcd->data, devcd->datalen);
> >  }
> >  
> > -static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
> > -				struct bin_attribute *bin_attr,
> > -				char *buffer, loff_t offset, size_t count)
> > +static void devcd_remove_now(struct devcd_entry *devcd)
> 
> this function can also be used by devcd_free().

well, indeed.
And perhaps using the

flush_delayed_work(&devcd->del_wk);

instead of

mod_delayed_work(system_wq, &devcd->del_wk, 0);

and then I don't even need to switch from
INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
to
devm_delayed_work_autocancel()

since it will be flushed, so no need to autocancel it.

Johannes, any hard preference or request from your side?

Thanks,
Rodrigo.

> 
> Other than that LGTM.
> 
> >  {
> > -	struct device *dev = kobj_to_dev(kobj);
> > -	struct devcd_entry *devcd = dev_to_devcd(dev);
> > -
> >  	mutex_lock(&devcd->mutex);
> >  	if (!devcd->delete_work) {
> >  		devcd->delete_work = true;
> >  		mod_delayed_work(system_wq, &devcd->del_wk, 0);
> >  	}
> >  	mutex_unlock(&devcd->mutex);
> > +}
> > +
> > +static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
> > +				struct bin_attribute *bin_attr,
> > +				char *buffer, loff_t offset, size_t count)
> > +{
> > +	struct device *dev = kobj_to_dev(kobj);
> > +	struct devcd_entry *devcd = dev_to_devcd(dev);
> > +
> > +	devcd_remove_now(devcd);
> >  
> >  	return count;
> >  }
> > @@ -304,6 +310,12 @@ static ssize_t devcd_read_from_sgtable(char *buffer, loff_t offset,
> >  				  offset);
> >  }
> >  
> > +static void devcd_remove(void *data)
> > +{
> > +	struct devcd_entry *devcd = data;
> > +	devcd_remove_now(devcd);
> > +}
> > +
> >  /**
> >   * dev_coredumpm - create device coredump with read/free methods
> >   * @dev: the struct device for the crashed device
> > @@ -379,7 +391,10 @@ void dev_coredumpm(struct device *dev, struct module *owner,
> >  
> >  	dev_set_uevent_suppress(&devcd->devcd_dev, false);
> >  	kobject_uevent(&devcd->devcd_dev.kobj, KOBJ_ADD);
> > -	INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
> > +	if (devm_add_action(dev, devcd_remove, devcd))
> > +		dev_warn(dev, "devcoredump managed auto-removal registration failed\n");
> > +	if (devm_delayed_work_autocancel(dev, &devcd->del_wk, devcd_del))
> > +		dev_warn(dev, "devcoredump managed autocancel work failed\n");
> >  	schedule_delayed_work(&devcd->del_wk, DEVCD_TIMEOUT);
> >  	mutex_unlock(&devcd->mutex);
> >  	return;
>