[PATCH 5.15 168/279] NFC: reorganize the functions in nci_request

Greg Kroah-Hartman
2021-11-24T13:56:50Z

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

[ Upstream commit 86cdf8e38792545161dbe3350a7eced558ba4d15 ]

There is a possible data race as shown below:

thread-A in nci_request() | thread-B in nci_close_device()
| mutex_lock(&ndev->req_lock);
test_bit(NCI_UP, &ndev->flags); |
... | test_and_clear_bit(NCI_UP, &ndev->flags)
mutex_lock(&ndev->req_lock); |
|

This race will allow __nci_request() to be awaked while the device is
getting removed.

Similar to commit e2cb6b891ad2 ("bluetooth: eliminate the potential race
condition when removing the HCI controller"). this patch alters the
function sequence in nci_request() to prevent the data races between the
nci_close_device().

Signed-off-by: Lin Ma <linma@zju.edu.cn>
Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
Link: https://lore.kernel.org/r/20211115145600.8320-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/nfc/nci/core.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index 82ab39d80726e..39994dbb6a55b 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -144,12 +144,15 @@ inline int nci_request(struct nci_dev *ndev,
{
int rc;

- if (!test_bit(NCI_UP, &ndev->flags))
- return -ENETDOWN;
-
/* Serialize all requests */
mutex_lock(&ndev->req_lock);
- rc = __nci_request(ndev, req, opt, timeout);
+ /* check the state after obtaing the lock against any races
+ * from nci_close_device when the device gets removed.
+ */
+ if (test_bit(NCI_UP, &ndev->flags))
+ rc = __nci_request(ndev, req, opt, timeout);
+ else
+ rc = -ENETDOWN;
mutex_unlock(&ndev->req_lock);

return rc;
--
2.33.0