CVE-2026-64539Bluetooth: eir: Fix stack OOB write when prepending the Flags AD

Official description

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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/0f0b6232af56441d0a2dcb173cc4f8d8aab39014
• https://git.kernel.org/stable/c/9174992ee1045c9c96e53eecda64f49dd7e8fbba
• https://git.kernel.org/stable/c/09301f1fdf2aef8cce34d0c4650c30e7edb1ced9
• https://git.kernel.org/stable/c/f1b4df9c260c51726da2e86e19322825fddeefd0
• https://git.kernel.org/stable/c/57077eeb586c42f124bc09e018449362223067b3
• https://git.kernel.org/stable/c/6f5fb689fdf80bdd143f22a502f9eb1f3c85e286