CVE-2022-49908 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: L2CAP: Fix memory leak in vhci_write
Syzkaller reports a memory leak as follows: ==================================== BUG: memory leak unreferenced object 0xffff88810d81ac00 (size 240): [...]
hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [] __alloc_skb+0x1f9/0x270 net/core/skbuff.c:418
[] alloc_skb include/linux/skbuff.h:1257 [inline]
[] bt_skb_alloc include/net/bluetooth/bluetooth.h:469 [inline]
[] vhci_get_user drivers/bluetooth/hci_vhci.c:391 [inline]
[] vhci_write+0x5f/0x230 drivers/bluetooth/hci_vhci.c:511
[] call_write_iter include/linux/fs.h:2192 [inline]
[] new_sync_write fs/read_write.c:491 [inline]
[] vfs_write+0x42d/0x540 fs/read_write.c:578
[] ksys_write+0x9d/0x160 fs/read_write.c:631
[] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
[] entry_SYSCALL_64_after_hwframe+0x63/0xcd
====================================
HCI core will uses hci_rx_work() to process frame, which is queued to the hdev->rx_q tail in hci_recv_frame() by HCI driver.
Yet the problem is that, HCI core may not free the skb after handling ACL data packets. To be more specific, when start fragment does not contain the L2CAP length, HCI core just copies skb into conn->rx_skb and finishes frame process in l2cap_recv_acldata(), without freeing the skb, which triggers the above memory leak.
This patch solves it by releasing the relative skb, after processing the above case in l2cap_recv_acldata().
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Analysis
by VulDB Data Team • 05/01/2025
The vulnerability CVE-2022-49908 represents a memory leak in the Linux kernel's Bluetooth implementation, specifically within the L2CAP (Logical Link Control and Adaptation Protocol) layer of the HCI (Host Controller Interface) subsystem. This issue was identified through syzkaller, an automated fuzzer that systematically tests kernel code paths to discover potential vulnerabilities. The memory leak occurs in the vhci_write function within the virtual HCI driver implementation, which handles Bluetooth communication through virtual devices. The flaw manifests when processing Bluetooth ACL (Asynchronous Connection-Less) data packets where the initial fragment of a data frame does not contain the complete L2CAP length field, leading to improper memory management and eventual resource exhaustion.
The technical root cause stems from improper handling of socket buffer (skb) memory management within the Bluetooth subsystem's packet processing pipeline. When the HCI core receives an ACL data packet through hci_recv_frame(), it queues the frame to the hdev->rx_q queue for processing. However, under specific conditions where the first fragment lacks the L2CAP length information, the system copies the skb into conn->rx_skb but fails to properly release the original skb memory. This occurs within the l2cap_recv_acldata() function, which processes ACL data but does not account for the memory cleanup required when the L2CAP length field is missing from the initial fragment. The backtrace shows the allocation path starting from __alloc_skb through bt_skb_alloc and ending in vhci_write, indicating the memory allocation occurs in the Bluetooth-specific socket buffer management layer.
The operational impact of this vulnerability extends beyond simple memory consumption, potentially leading to system instability and performance degradation in Bluetooth-enabled devices. The memory leak represents a classic case of resource management failure that can accumulate over time, especially in systems with active Bluetooth connections or frequent Bluetooth operations. This vulnerability aligns with CWE-401: "Improper Release of Memory" and demonstrates how improper handling of kernel memory structures can create persistent resource exhaustion conditions. The issue particularly affects systems running Linux kernels with virtual HCI drivers enabled, which are commonly found in development environments, virtualized systems, and embedded platforms that utilize Bluetooth virtualization for testing or simulation purposes.
The mitigation strategy involves implementing proper memory cleanup within the l2cap_recv_acldata() function when processing the specific case where the L2CAP length field is missing from the initial fragment. The fix ensures that the skb memory is released after processing the case, preventing the accumulation of unreferenced memory blocks. This approach follows established kernel development practices for memory management and aligns with ATT&CK technique T1070.004: "File and Directory Permissions Modification" in the context of system resource management. The patch demonstrates proper defensive programming by ensuring that all allocated memory paths include appropriate cleanup mechanisms, preventing the memory leak from occurring in the first place. This vulnerability highlights the importance of rigorous memory management in kernel space operations and the necessity of comprehensive testing for edge cases in protocol implementations.