[PATCH 4.4 139/162] NFC: reorder the logic in nfc_{un,}register_device

Greg Kroah-Hartman
2021-11-24T12:11:05Z

From: Lin Ma <linma@zju.edu.cn>

[ Upstream commit 3e3b5dfcd16a3e254aab61bd1e8c417dd4503102 ]

There is a potential UAF between the unregistration routine and the NFC
netlink operations.

The race that cause that UAF can be shown as below:

(FREE) | (USE)
nfcmrvl_nci_unregister_dev | nfc_genl_dev_up
nci_close_device |
nci_unregister_device | nfc_get_device
nfc_unregister_device | nfc_dev_up
rfkill_destory |
device_del | rfkill_blocked
... | ...

The root cause for this race is concluded below:
1. The rfkill_blocked (USE) in nfc_dev_up is supposed to be placed after
the device_is_registered check.
2. Since the netlink operations are possible just after the device_add
in nfc_register_device, the nfc_dev_up() can happen anywhere during the
rfkill creation process, which leads to data race.

This patch reorder these actions to permit
1. Once device_del is finished, the nfc_dev_up cannot dereference the
rfkill object.
2. The rfkill_register need to be placed after the device_add of nfc_dev
because the parent device need to be created first. So this patch keeps
the order but inject device_lock to prevent the data race.

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Fixes: be055b2f89b5 ("NFC: RFKILL support")
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20211116152652.19217-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/nfc/core.c | 32 ++++++++++++++++++--------------
1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/net/nfc/core.c b/net/nfc/core.c
index 1471e4b0aa2c6..8c7f221e1d125 100644
--- a/net/nfc/core.c
+++ b/net/nfc/core.c
@@ -106,13 +106,13 @@ int nfc_dev_up(struct nfc_dev *dev)

device_lock(&dev->dev);

- if (dev->rfkill && rfkill_blocked(dev->rfkill)) {
- rc = -ERFKILL;
+ if (!device_is_registered(&dev->dev)) {
+ rc = -ENODEV;
goto error;
}

- if (!device_is_registered(&dev->dev)) {
- rc = -ENODEV;
+ if (dev->rfkill && rfkill_blocked(dev->rfkill)) {
+ rc = -ERFKILL;
goto error;
}

@@ -1120,11 +1120,7 @@ int nfc_register_device(struct nfc_dev *dev)
if (rc)
pr_err("Could not register llcp device\n");

- rc = nfc_genl_device_added(dev);
- if (rc)
- pr_debug("The userspace won't be notified that the device %s was added\n",
- dev_name(&dev->dev));
-
+ device_lock(&dev->dev);
dev->rfkill = rfkill_alloc(dev_name(&dev->dev), &dev->dev,
RFKILL_TYPE_NFC, &nfc_rfkill_ops, dev);
if (dev->rfkill) {
@@ -1133,6 +1129,12 @@ int nfc_register_device(struct nfc_dev *dev)
dev->rfkill = NULL;
}
}
+ device_unlock(&dev->dev);
+
+ rc = nfc_genl_device_added(dev);
+ if (rc)
+ pr_debug("The userspace won't be notified that the device %s was added\n",
+ dev_name(&dev->dev));

return 0;
}
@@ -1149,10 +1151,17 @@ void nfc_unregister_device(struct nfc_dev *dev)

pr_debug("dev_name=%s\n", dev_name(&dev->dev));

+ rc = nfc_genl_device_removed(dev);
+ if (rc)
+ pr_debug("The userspace won't be notified that the device %s "
+ "was removed\n", dev_name(&dev->dev));
+
+ device_lock(&dev->dev);
if (dev->rfkill) {
rfkill_unregister(dev->rfkill);
rfkill_destroy(dev->rfkill);
}
+ device_unlock(&dev->dev);

if (dev->ops->check_presence) {
device_lock(&dev->dev);
@@ -1162,11 +1171,6 @@ void nfc_unregister_device(struct nfc_dev *dev)
cancel_work_sync(&dev->check_pres_work);
}

- rc = nfc_genl_device_removed(dev);
- if (rc)
- pr_debug("The userspace won't be notified that the device %s "
- "was removed\n", dev_name(&dev->dev));
-
nfc_llcp_unregister_device(dev);

mutex_lock(&nfc_devlist_mutex);
--
2.33.0