Bluetooth: eir: Fix stack OOB write when prepending the Flags AD

Overview

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: eir: Fix stack OOB write when prepending the Flags AD

eir_create_adv_data() builds the advertising data into a fixed-size buffer ("size", 31 for the legacy path). It may prepend a 3-byte "Flags" AD structure (LE_AD_NO_BREDR on an LE-only controller) and then copies the per-instance data without checking that it still fits:

memcpy(ptr, adv->adv_data, adv->adv_data_len);

tlv_data_max_len() only reserves those 3 bytes when the user-supplied flags carry a managed-flags bit, so an instance added with flags == 0 is accepted with adv_data_len up to the full buffer. At advertise time the flags are still prepended, and the memcpy() writes 3 + adv_data_len bytes into the size-byte buffer:

BUG: KASAN: stack-out-of-bounds in eir_create_adv_data (net/bluetooth/eir.c:301) Write of size 31 at addr ffff88800a547bdc by task kworker/u9:0/65 Workqueue: hci0 hci_cmd_sync_work __asan_memcpy (mm/kasan/shadow.c:106) eir_create_adv_data (net/bluetooth/eir.c:301) hci_update_adv_data_sync (net/bluetooth/hci_sync.c:1310) hci_schedule_adv_instance_sync (net/bluetooth/hci_sync.c:1817) hci_cmd_sync_work (net/bluetooth/hci_sync.c:332) This frame has 1 object: [32, 64) 'cp'

The "Flags" structure is added by the kernel, not requested by userspace, so only prepend it when it fits together with the instance advertising data; when there is no room for both, drop the flags rather than the user-provided data.

Reachable by a local user with CAP_NET_ADMIN owning an LE-only controller on the legacy advertising path.

Affected

• Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 0f0b6232af56441d0a2dcb173cc4f8d8aab39014
• Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 09301f1fdf2aef8cce34d0c4650c30e7edb1ced9
• Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < f1b4df9c260c51726da2e86e19322825fddeefd0
• Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 57077eeb586c42f124bc09e018449362223067b3
• Linux >= b44133ff03be30b55f23036e62f403a3f7784fce < 6f5fb689fdf80bdd143f22a502f9eb1f3c85e286
• Linux 4.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.