CVE-2022-49909 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: L2CAP: fix use-after-free in l2cap_conn_del()
When l2cap_recv_frame() is invoked to receive data, and the cid is L2CAP_CID_A2MP, if the channel does not exist, it will create a channel. However, after a channel is created, the hold operation of the channel is not performed. In this case, the value of channel reference counting is 1. As a result, after hci_error_reset() is triggered, l2cap_conn_del() invokes the close hook function of A2MP to release the channel. Then l2cap_chan_unlock(chan) will trigger UAF issue.
The process is as follows: Receive data: l2cap_data_channel() a2mp_channel_create() --->channel ref is 2 l2cap_chan_put() --->channel ref is 1
Triger event: hci_error_reset() hci_dev_do_close() ... l2cap_disconn_cfm() l2cap_conn_del() l2cap_chan_hold() --->channel ref is 2 l2cap_chan_del() --->channel ref is 1 a2mp_chan_close_cb() --->channel ref is 0, release channel l2cap_chan_unlock() --->UAF of channel
The detailed Call Trace is as follows: BUG: KASAN: use-after-free in __mutex_unlock_slowpath+0xa6/0x5e0 Read of size 8 at addr ffff8880160664b8 by task kworker/u11:1/7593 Workqueue: hci0 hci_error_reset Call Trace: dump_stack_lvl+0xcd/0x134 print_report.cold+0x2ba/0x719 kasan_report+0xb1/0x1e0 kasan_check_range+0x140/0x190 __mutex_unlock_slowpath+0xa6/0x5e0 l2cap_conn_del+0x404/0x7b0 l2cap_disconn_cfm+0x8c/0xc0 hci_conn_hash_flush+0x11f/0x260 hci_dev_close_sync+0x5f5/0x11f0 hci_dev_do_close+0x2d/0x70 hci_error_reset+0x9e/0x140 process_one_work+0x98a/0x1620 worker_thread+0x665/0x1080 kthread+0x2e4/0x3a0 ret_from_fork+0x1f/0x30
Allocated by task 7593: kasan_save_stack+0x1e/0x40 __kasan_kmalloc+0xa9/0xd0 l2cap_chan_create+0x40/0x930 amp_mgr_create+0x96/0x990 a2mp_channel_create+0x7d/0x150 l2cap_recv_frame+0x51b8/0x9a70 l2cap_recv_acldata+0xaa3/0xc00 hci_rx_work+0x702/0x1220 process_one_work+0x98a/0x1620 worker_thread+0x665/0x1080 kthread+0x2e4/0x3a0 ret_from_fork+0x1f/0x30
Freed by task 7593: kasan_save_stack+0x1e/0x40 kasan_set_track+0x21/0x30 kasan_set_free_info+0x20/0x30 ____kasan_slab_free+0x167/0x1c0 slab_free_freelist_hook+0x89/0x1c0 kfree+0xe2/0x580 l2cap_chan_put+0x22a/0x2d0 l2cap_conn_del+0x3fc/0x7b0 l2cap_disconn_cfm+0x8c/0xc0 hci_conn_hash_flush+0x11f/0x260 hci_dev_close_sync+0x5f5/0x11f0 hci_dev_do_close+0x2d/0x70 hci_error_reset+0x9e/0x140 process_one_work+0x98a/0x1620 worker_thread+0x665/0x1080 kthread+0x2e4/0x3a0 ret_from_fork+0x1f/0x30
Last potentially related work creation: kasan_save_stack+0x1e/0x40 __kasan_record_aux_stack+0xbe/0xd0 call_rcu+0x99/0x740 netlink_release+0xe6a/0x1cf0 __sock_release+0xcd/0x280 sock_close+0x18/0x20 __fput+0x27c/0xa90 task_work_run+0xdd/0x1a0 exit_to_user_mode_prepare+0x23c/0x250 syscall_exit_to_user_mode+0x19/0x50 do_syscall_64+0x42/0x80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Second to last potentially related work creation: kasan_save_stack+0x1e/0x40 __kasan_record_aux_stack+0xbe/0xd0 call_rcu+0x99/0x740 netlink_release+0xe6a/0x1cf0 __sock_release+0xcd/0x280 sock_close+0x18/0x20 __fput+0x27c/0xa90 task_work_run+0xdd/0x1a0 exit_to_user_mode_prepare+0x23c/0x250 syscall_exit_to_user_mode+0x19/0x50 do_syscall_64+0x42/0x80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
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Analysis
by VulDB Data Team • 05/09/2026
The vulnerability described represents a use-after-free condition in the Linux kernel's Bluetooth implementation, specifically within the L2CAP (Logical Link Control and Adaptation Protocol) subsystem. This issue manifests in the l2cap_conn_del() function and arises from improper handling of reference counting for Bluetooth channels during error reset scenarios. The flaw occurs when l2cap_recv_frame() processes incoming data with a cid value of L2CAP_CID_A2MP, which indicates an A2MP (Audio/Video Distribution Profile Management Protocol) channel. When such a channel does not exist, the system creates it but fails to properly increment the channel's reference count through the hold operation. This creates a scenario where the channel reference count remains at one, despite the channel being created and subsequently freed improperly.
The technical execution path begins with the reception of data through l2cap_data_channel() which triggers a2mp_channel_create() resulting in a channel reference count of two. Subsequently, l2cap_chan_put() reduces this count to one, but the channel remains in an inconsistent state. When hci_error_reset() is invoked, the system executes a series of operations that ultimately call l2cap_conn_del(). This function performs l2cap_chan_hold() which increases the reference count to two, followed by l2cap_chan_del() that decrements it back to one, and finally a2mp_chan_close_cb() that reduces it to zero, triggering the channel release. The subsequent l2cap_chan_unlock() operation attempts to access memory that has already been freed, leading to the use-after-free condition. The kernel's memory safety checker (KASAN) detects this issue during the __mutex_unlock_slowpath operation, which occurs when trying to release a mutex that protects the freed channel structure.
This vulnerability directly maps to CWE-416, which defines the use-after-free weakness, and aligns with ATT&CK technique T1059.006 for command and scripting interpreter execution in kernel space. The operational impact of this vulnerability is severe as it can lead to arbitrary code execution, system crashes, or privilege escalation within the kernel context. An attacker could potentially exploit this condition by triggering the specific error reset scenario, causing the kernel to execute code in the context of freed memory, which may allow for bypassing security controls and executing malicious payloads. The vulnerability affects all Linux kernel versions that implement the affected Bluetooth L2CAP subsystem and specifically targets systems with Bluetooth functionality enabled. The attack surface is limited to systems that process Bluetooth A2MP frames and experience the specific error conditions that trigger hci_error_reset(), but the potential for exploitation makes this a critical security concern for embedded systems, mobile devices, and servers with Bluetooth capabilities.
The root cause of this vulnerability stems from improper reference counting management during channel lifecycle operations within the Bluetooth subsystem. The missing hold operation after channel creation creates a race condition between the channel creation and destruction phases. When the system processes error conditions through hci_error_reset(), the subsequent cleanup operations assume proper reference counting, but the inconsistent state leads to double-free or use-after-free conditions. The fix for this vulnerability requires ensuring that proper reference counting is maintained throughout the channel lifecycle, specifically ensuring that l2cap_chan_hold() is called after channel creation to properly increment the reference count before any error handling paths are executed. This aligns with standard kernel development practices for managing reference-counted objects and preventing use-after-free vulnerabilities. The recommended mitigation involves applying the kernel patch that corrects the reference counting logic in l2cap_conn_del() and related functions, ensuring that channel hold operations are properly synchronized with channel creation and destruction events. Additionally, system administrators should ensure their kernel versions include the patched code, particularly in environments where Bluetooth functionality is exposed to untrusted networks or users.