2021-11-15 14:56:55

by Lin Ma

Subject: [PATCH v1] NFC: reorganize the functions in nci_request

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 <[email protected]>
Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")
---
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 6fd873aa86be..1dd0269c1a72 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;
--
2.33.1

2021-11-15 14:58:24

by Lin Ma

Subject: CHANGELOG: [PATCH v1] NFC: reorganize the functions in nci_request

Hi there,

Compared to the version-0 patch, this patch add fixes tag in the patch file

+ Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")


Best regards
Lin

2021-11-17 09:32:51

by Krzysztof Kozlowski

Subject: Re: CHANGELOG: [PATCH v1] NFC: reorganize the functions in nci_request

On 15/11/2021 15:57, Lin Ma wrote:
> Hi there,
>
> Compared to the version-0 patch, this patch add fixes tag in the patch file
>
> + Fixes: 6a2968aaf50c ("NFC: basic NCI protocol implementation")

Changelog goes either as cover letter (git help format-patch) or after
'---' separator to individual patch.

Best regards,
Krzysztof

2021-11-18 04:30:38

by patchwork-bot+netdevbpf

Subject: Re: [PATCH v1] NFC: reorganize the functions in nci_request

Hello:

This patch was applied to netdev/net.git (master)
by Jakub Kicinski <[email protected]>:

On Mon, 15 Nov 2021 22:56:00 +0800 you wrote:
> 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); |
> |
>
> [...]

Here is the summary with links:
- [v1] NFC: reorganize the functions in nci_request
https://git.kernel.org/netdev/net/c/86cdf8e38792

You are awesome, thank you!
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