From: Lin Ma <linma@xxxxxxxxxx> [ Upstream commit 0fc044b2b5e2d05a1fa1fb0d7f270367a7855d79 ] dvb_unregister_device() is known that prone to use-after-free. That is, the cleanup from dvb_unregister_device() releases the dvb_device even if there are pointers stored in file->private_data still refer to it. This patch adds a reference counter into struct dvb_device and delays its deallocation until no pointer refers to the object. Link: https://lore.kernel.org/linux-media/20220807145952.10368-1-linma@xxxxxxxxxx Signed-off-by: Lin Ma <linma@xxxxxxxxxx> Reported-by: kernel test robot <lkp@xxxxxxxxx> Signed-off-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/media/dvb-core/dvb_ca_en50221.c | 2 +- drivers/media/dvb-core/dvb_frontend.c | 2 +- drivers/media/dvb-core/dvbdev.c | 32 +++++++++++++++++++------ include/media/dvbdev.h | 31 +++++++++++++----------- 4 files changed, 44 insertions(+), 23 deletions(-) diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c index cfc27629444f..fd476536d32e 100644 --- a/drivers/media/dvb-core/dvb_ca_en50221.c +++ b/drivers/media/dvb-core/dvb_ca_en50221.c @@ -157,7 +157,7 @@ static void dvb_ca_private_free(struct dvb_ca_private *ca) { unsigned int i; - dvb_free_device(ca->dvbdev); + dvb_device_put(ca->dvbdev); for (i = 0; i < ca->slot_count; i++) vfree(ca->slot_info[i].rx_buffer.data); diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c index 06ea30a689d7..e18ed517db98 100644 --- a/drivers/media/dvb-core/dvb_frontend.c +++ b/drivers/media/dvb-core/dvb_frontend.c @@ -135,7 +135,7 @@ static void __dvb_frontend_free(struct dvb_frontend *fe) struct dvb_frontend_private *fepriv = fe->frontend_priv; if (fepriv) - dvb_free_device(fepriv->dvbdev); + dvb_device_put(fepriv->dvbdev); dvb_frontend_invoke_release(fe, fe->ops.release); diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c index ec9ebff28552..7b28b483e4b2 100644 --- a/drivers/media/dvb-core/dvbdev.c +++ b/drivers/media/dvb-core/dvbdev.c @@ -107,7 +107,7 @@ static int dvb_device_open(struct inode *inode, struct file *file) new_fops = fops_get(dvbdev->fops); if (!new_fops) goto fail; - file->private_data = dvbdev; + file->private_data = dvb_device_get(dvbdev); replace_fops(file, new_fops); if (file->f_op->open) err = file->f_op->open(inode, file); @@ -171,6 +171,9 @@ int dvb_generic_release(struct inode *inode, struct file *file) } dvbdev->users++; + + dvb_device_put(dvbdev); + return 0; } EXPORT_SYMBOL(dvb_generic_release); @@ -487,6 +490,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev, return -ENOMEM; } + kref_init(&dvbdev->ref); memcpy(dvbdev, template, sizeof(struct dvb_device)); dvbdev->type = type; dvbdev->id = id; @@ -517,7 +521,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev, #endif dvbdev->minor = minor; - dvb_minors[minor] = dvbdev; + dvb_minors[minor] = dvb_device_get(dvbdev); up_write(&minor_rwsem); ret = dvb_register_media_device(dvbdev, type, minor, demux_sink_pads); @@ -557,6 +561,7 @@ void dvb_remove_device(struct dvb_device *dvbdev) down_write(&minor_rwsem); dvb_minors[dvbdev->minor] = NULL; + dvb_device_put(dvbdev); up_write(&minor_rwsem); dvb_media_device_free(dvbdev); @@ -568,21 +573,34 @@ void dvb_remove_device(struct dvb_device *dvbdev) EXPORT_SYMBOL(dvb_remove_device); -void dvb_free_device(struct dvb_device *dvbdev) +static void dvb_free_device(struct kref *ref) { - if (!dvbdev) - return; + struct dvb_device *dvbdev = container_of(ref, struct dvb_device, ref); kfree (dvbdev->fops); kfree (dvbdev); } -EXPORT_SYMBOL(dvb_free_device); + + +struct dvb_device *dvb_device_get(struct dvb_device *dvbdev) +{ + kref_get(&dvbdev->ref); + return dvbdev; +} +EXPORT_SYMBOL(dvb_device_get); + + +void dvb_device_put(struct dvb_device *dvbdev) +{ + if (dvbdev) + kref_put(&dvbdev->ref, dvb_free_device); +} void dvb_unregister_device(struct dvb_device *dvbdev) { dvb_remove_device(dvbdev); - dvb_free_device(dvbdev); + dvb_device_put(dvbdev); } EXPORT_SYMBOL(dvb_unregister_device); diff --git a/include/media/dvbdev.h b/include/media/dvbdev.h index e547cbeee431..6e736587aa1f 100644 --- a/include/media/dvbdev.h +++ b/include/media/dvbdev.h @@ -156,6 +156,7 @@ struct dvb_adapter { */ struct dvb_device { struct list_head list_head; + struct kref ref; const struct file_operations *fops; struct dvb_adapter *adapter; enum dvb_device_type type; @@ -187,6 +188,20 @@ struct dvb_device { void *priv; }; +/** + * dvb_device_get - Increase dvb_device reference + * + * @dvbdev: pointer to struct dvb_device + */ +struct dvb_device *dvb_device_get(struct dvb_device *dvbdev); + +/** + * dvb_device_get - Decrease dvb_device reference + * + * @dvbdev: pointer to struct dvb_device + */ +void dvb_device_put(struct dvb_device *dvbdev); + /** * dvb_register_adapter - Registers a new DVB adapter * @@ -231,29 +246,17 @@ int dvb_register_device(struct dvb_adapter *adap, /** * dvb_remove_device - Remove a registered DVB device * - * This does not free memory. To do that, call dvb_free_device(). + * This does not free memory. dvb_free_device() will do that when + * reference counter is empty * * @dvbdev: pointer to struct dvb_device */ void dvb_remove_device(struct dvb_device *dvbdev); -/** - * dvb_free_device - Free memory occupied by a DVB device. - * - * Call dvb_unregister_device() before calling this function. - * - * @dvbdev: pointer to struct dvb_device - */ -void dvb_free_device(struct dvb_device *dvbdev); /** * dvb_unregister_device - Unregisters a DVB device * - * This is a combination of dvb_remove_device() and dvb_free_device(). - * Using this function is usually a mistake, and is often an indicator - * for a use-after-free bug (when a userspace process keeps a file - * handle to a detached device). - * * @dvbdev: pointer to struct dvb_device */ void dvb_unregister_device(struct dvb_device *dvbdev); -- 2.35.1
