In min_key_size_set(): if (val > hdev->le_max_key_size || val < SMP_MIN_ENC_KEY_SIZE) return -EINVAL; hci_dev_lock(hdev); hdev->le_min_key_size = val; hci_dev_unlock(hdev);

In max_key_size_set(): if (val > SMP_MAX_ENC_KEY_SIZE || val < hdev->le_min_key_size) return -EINVAL; hci_dev_lock(hdev); hdev->le_max_key_size = val; hci_dev_unlock(hdev);

The atomicity violation occurs due to concurrent execution of set_min and set_max funcs.Consider a scenario where setmin writes a new, valid 'min' value, and concurrently, setmax writes a value that is greater than the old 'min' but smaller than the new 'min'. In this case, setmax might check against the old 'min' value (before acquiring the lock) but write its value after the 'min' has been updated by setmin. This leads to a situation where the 'max' value ends up being smaller than the 'min' value, which is an inconsistency.

This possible bug is found by an experimental static analysis tool developed by our team, BassCheck[1]. This tool analyzes the locking APIs to extract function pairs that can be concurrently executed, and then analyzes the instructions in the paired functions to identify possible concurrency bugs including data races and atomicity violations. The above possible bug is reported when our tool analyzes the source code of Linux 5.17.

To resolve this issue, it is suggested to encompass the validity checks within the locked sections in both set_min and set_max funcs. The modification ensures that the validation of 'val' against the current min/max values is atomic, thus maintaining the integrity of the settings. With this patch applied, our tool no longer reports the bug, with the kernel configuration allyesconfig for x86_64. Due to the lack of associated hardware, we cannot test the patch in runtime testing, and just verify it according to the code logic.

[1] https://sites.google.com/view/basscheck/

Fixes: 18f81241b74f ("Bluetooth: Move {min,max}_key_size debugfs ...") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han 2045gemini@gmail.com --- v2: * Adjust the format to pass the CI. --- net/bluetooth/hci_debugfs.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c index 6b7741f6e95b..3ffbf3f25363 100644 --- a/net/bluetooth/hci_debugfs.c +++ b/net/bluetooth/hci_debugfs.c @@ -1045,11 +1045,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(adv_max_interval_fops, adv_max_interval_get, static int min_key_size_set(void *data, u64 val) { struct hci_dev *hdev = data; - - if (val > hdev->le_max_key_size || val < SMP_MIN_ENC_KEY_SIZE) + + hci_dev_lock(hdev); + if (val > hdev->le_max_key_size || val < SMP_MIN_ENC_KEY_SIZE) { + hci_dev_unlock(hdev); return -EINVAL; + }

- hci_dev_lock(hdev); hdev->le_min_key_size = val; hci_dev_unlock(hdev);

@@ -1073,11 +1075,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(min_key_size_fops, min_key_size_get, static int max_key_size_set(void *data, u64 val) { struct hci_dev *hdev = data; - - if (val > SMP_MAX_ENC_KEY_SIZE || val < hdev->le_min_key_size) + + hci_dev_lock(hdev); + if (val > SMP_MAX_ENC_KEY_SIZE || val < hdev->le_min_key_size) { + hci_dev_unlock(hdev); return -EINVAL; + }

- hci_dev_lock(hdev); hdev->le_max_key_size = val; hci_dev_unlock(hdev);