Gui-Dong Han
4c71c01df8
commitda9065caa5upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.