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Bluetooth: Fix atomicity violation in {min,max}_key_size_set

Browse Source 
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: 18f81241b7 ("Bluetooth: Move {min,max}_key_size debugfs ...")
Cc: stable@vger.kernel.org
Signed-off-by: Gui-Dong Han <2045gemini@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
This commit is contained in:
Gui-Dong Han 2023-12-22 23:12:41 +08:00 committed by Luiz Augusto von Dentz
parent 3600860a71
commit da9065caa5
1 changed files with 10 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
net/bluetooth/hci_debugfs.c
View File

@ -1046,10 +1046,12 @@ 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)
return -EINVAL;
hci_dev_lock(hdev);
if (val > hdev->le_max_key_size || val < SMP_MIN_ENC_KEY_SIZE) {
hci_dev_unlock(hdev);
return -EINVAL;
}
hdev->le_min_key_size = val;
hci_dev_unlock(hdev);
@ -1074,10 +1076,12 @@ 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)
return -EINVAL;
hci_dev_lock(hdev);
if (val > SMP_MAX_ENC_KEY_SIZE || val < hdev->le_min_key_size) {
hci_dev_unlock(hdev);
return -EINVAL;
}
hdev->le_max_key_size = val;
hci_dev_unlock(hdev);