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fsi: master: Clarify master lifetimes & fix use-after-free in hub master 

Once we call fsi_master_unregister, the core will put_device,
potentially freeing the hub master. This change adds a comment
explaining the lifetime of an allocated fsi_master.

We then add a reference from the driver to the hub master, so it stays
around until we've finished ->remove().

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Tested-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Jeremy Kerr 2018-02-12 15:45:47 +10:30 committed by Greg Kroah-Hartman
parent 638bd9ac84
commit e0c24bddf0
2 changed files with 33 additions and 3 deletions
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21
drivers/fsi/fsi-master-hub.c
View File

@ -288,10 +288,19 @@ static int hub_master_probe(struct device *dev)
hub_master_init(hub);
rc = fsi_master_register(&hub->master);
if (!rc)
return 0;
if (rc)
goto err_release;
/* At this point, fsi_master_register performs the device_initialize(),
* and holds the sole reference on master.dev. This means the device
* will be freed (via ->release) during any subsequent call to
* fsi_master_unregister. We add our own reference to it here, so we
* can perform cleanup (in _remove()) without it being freed before
* we're ready.
*/
get_device(&hub->master.dev);
return 0;
kfree(hub);
err_release:
fsi_slave_release_range(fsi_dev->slave, FSI_HUB_LINK_OFFSET,
FSI_HUB_LINK_SIZE * links);
@ -306,6 +315,12 @@ static int hub_master_remove(struct device *dev)
fsi_slave_release_range(hub->upstream->slave, hub->addr, hub->size);
of_node_put(hub->master.dev.of_node);
/*
* master.dev will likely be ->release()ed after this, which free()s
* the hub
*/
put_device(&hub->master.dev);
return 0;
}

15
drivers/fsi/fsi-master.h
View File

@ -37,6 +37,21 @@ struct fsi_master {
#define dev_to_fsi_master(d) container_of(d, struct fsi_master, dev)
/**
* fsi_master registration & lifetime: the fsi_master_register() and
* fsi_master_unregister() functions will take ownership of the master, and
* ->dev in particular. The registration path performs a get_device(), which
* takes the first reference on the device. Similarly, the unregistration path
* performs a put_device(), which may well drop the last reference.
*
* This means that master implementations *may* need to hold their own
* reference (via get_device()) on master->dev. In particular, if the device's
* ->release callback frees the fsi_master, then fsi_master_unregister will
* invoke this free if no other reference is held.
*
* The same applies for the error path of fsi_master_register; if the call
* fails, dev->release will have been invoked.
*/
extern int fsi_master_register(struct fsi_master *master);
extern void fsi_master_unregister(struct fsi_master *master);