| Message ID | 20231222105526.9208-1-2045gemini@gmail.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Bluetooth: Fix atomicity violation in {conn,adv}_{min,max}_interval_set | expand |
Hi, Thanks for your feedback. Let me clarify the potential issue with concurrent execution of setmax and setmin functions. 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. Regarding the lock sequence you mentioned, it's indeed from the original code. My patch aims to include the validity checks within the lock/unlock sequence to prevent the described race condition. Thanks, Han On 22/12/2023 下午7:41, David Laight wrote: > From: Gui-Dong Han >> Sent: 22 December 2023 10:55 >> >> In {conn,adv}_min_interval_set(): >> if (val < ... || val > ... || val > hdev->le_{conn,adv}_max_interval) >> return -EINVAL; >> hci_dev_lock(hdev); >> hdev->le_{conn,adv}_min_interval = val; >> hci_dev_unlock(hdev); >> >> In {conn,adv}_max_interval_set(): >> if (val < ... || val > ... || val < hdev->le_{conn,adv}_min_interval) >> return -EINVAL; >> hci_dev_lock(hdev); >> hdev->le_{conn,adv}_max_interval >> hci_dev_unlock(hdev); >> >> The atomicity violation occurs due to concurrent execution of set_min and >> set_max funcs which may lead to inconsistent reads and writes of the min >> value and the max value. The checks for value validity are ineffective as >> the min/max values could change immediately after being checked, raising >> the risk of the min value being greater than the max value and causing >> invalid settings. >> >> 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. > Your static analysis tool is basically broken. > > The only possible issues are if the accesses aren't atomic. > In practise they always will be but using READ_ONCE() and > WRITE_ONCE() would make that certain. > > The lock sequence: >> hci_dev_lock(hdev); >> hdev->le_conn_min_interval = val; >> hci_dev_unlock(hdev); > is pretty pointless - is doesn't 'lock' two+ things together. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c index 6b7741f6e95b..6fdda807f2cf 100644 --- a/net/bluetooth/hci_debugfs.c +++ b/net/bluetooth/hci_debugfs.c @@ -849,11 +849,13 @@ DEFINE_SHOW_ATTRIBUTE(long_term_keys); static int conn_min_interval_set(void *data, u64 val) { struct hci_dev *hdev = data; - - if (val < 0x0006 || val > 0x0c80 || val > hdev->le_conn_max_interval) + + hci_dev_lock(hdev); + if (val < 0x0006 || val > 0x0c80 || val > hdev->le_conn_max_interval) { + hci_dev_unlock(hdev); return -EINVAL; + } - hci_dev_lock(hdev); hdev->le_conn_min_interval = val; hci_dev_unlock(hdev); @@ -877,11 +879,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(conn_min_interval_fops, conn_min_interval_get, static int conn_max_interval_set(void *data, u64 val) { struct hci_dev *hdev = data; - - if (val < 0x0006 || val > 0x0c80 || val < hdev->le_conn_min_interval) + + hci_dev_lock(hdev); + if (val < 0x0006 || val > 0x0c80 || val < hdev->le_conn_min_interval) { + hci_dev_unlock(hdev); return -EINVAL; + } - hci_dev_lock(hdev); hdev->le_conn_max_interval = val; hci_dev_unlock(hdev); @@ -989,11 +993,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(adv_channel_map_fops, adv_channel_map_get, static int adv_min_interval_set(void *data, u64 val) { struct hci_dev *hdev = data; - - if (val < 0x0020 || val > 0x4000 || val > hdev->le_adv_max_interval) + + hci_dev_lock(hdev); + if (val < 0x0020 || val > 0x4000 || val > hdev->le_adv_max_interval) { + hci_dev_unlock(hdev); return -EINVAL; + } - hci_dev_lock(hdev); hdev->le_adv_min_interval = val; hci_dev_unlock(hdev); @@ -1018,10 +1024,12 @@ static int adv_max_interval_set(void *data, u64 val) { struct hci_dev *hdev = data; - if (val < 0x0020 || val > 0x4000 || val < hdev->le_adv_min_interval) + hci_dev_lock(hdev); + if (val < 0x0020 || val > 0x4000 || val < hdev->le_adv_min_interval) { + hci_dev_unlock(hdev); return -EINVAL; + } - hci_dev_lock(hdev); hdev->le_adv_max_interval = val; hci_dev_unlock(hdev);
In {conn,adv}_min_interval_set(): if (val < ... || val > ... || val > hdev->le_{conn,adv}_max_interval) return -EINVAL; hci_dev_lock(hdev); hdev->le_{conn,adv}_min_interval = val; hci_dev_unlock(hdev); In {conn,adv}_max_interval_set(): if (val < ... || val > ... || val < hdev->le_{conn,adv}_min_interval) return -EINVAL; hci_dev_lock(hdev); hdev->le_{conn,adv}_max_interval hci_dev_unlock(hdev); The atomicity violation occurs due to concurrent execution of set_min and set_max funcs which may lead to inconsistent reads and writes of the min value and the max value. The checks for value validity are ineffective as the min/max values could change immediately after being checked, raising the risk of the min value being greater than the max value and causing invalid settings. 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: 3a5c82b78fd28 ("Bluetooth: Move LE debugfs file creation into ...") Cc: stable@vger.kernel.org Reported-by: BassCheck <bass@buaa.edu.cn> Signed-off-by: Gui-Dong Han <2045gemini@gmail.com> --- net/bluetooth/hci_debugfs.c | 30 +++++++++++++++++++----------- 1 file changed, 19 insertions(+), 11 deletions(-)