CVE-2017-9687 in Android
Summary
by MITRE
In Android for MSM, Firefox OS for MSM, QRD Android, with all Android releases from CAF using the Linux kernel, two concurrent threads/processes can write the value of "0" to the debugfs file that controls ipa ipc log which will lead to the double-free in ipc_log_context_destroy(). Another issue is the Use-After-Free which can happen due to the race condition when the ipc log is deallocated via the debugfs call during a log print.
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Analysis
by VulDB Data Team • 01/16/2021
This vulnerability exists in Android-based systems utilizing the Linux kernel from Code Aurora Forum with specific versions of MSM, Firefox OS, and QRD Android. The flaw stems from improper synchronization mechanisms within the kernel's handling of debugfs files that control IPA IPC logging functionality. The vulnerability manifests through a race condition between two concurrent threads or processes that attempt to write the value "0" to the same debugfs file simultaneously. This concurrent access pattern triggers a double-free condition in the ipc_log_context_destroy() function, which occurs when the same memory block is freed twice due to the improper handling of the race condition. The double-free vulnerability represents a classic memory corruption issue that can be exploited to gain arbitrary code execution or cause system instability. The root cause aligns with CWE-415 which describes improper handling of double-free conditions in memory management operations.
The secondary vulnerability involves a use-after-free scenario that emerges from the same race condition during the deallocation process of IPC logs through debugfs calls while log printing operations are still in progress. When one thread deallocates the IPC log context while another thread attempts to access or print to that same context, the system references freed memory, creating a use-after-free condition. This type of vulnerability typically allows attackers to manipulate memory contents or execute code by leveraging the freed memory locations for malicious purposes. The race condition itself is categorized under CWE-362 which describes improper synchronization leading to concurrent access issues, while the use-after-free pattern falls under CWE-416. Both vulnerabilities are particularly dangerous in kernel contexts as they can lead to privilege escalation and complete system compromise.
The operational impact of these vulnerabilities extends beyond simple system crashes or instability. The double-free condition can be exploited to cause denial of service attacks that may require system reboot or could potentially be leveraged for privilege escalation to kernel mode. The use-after-free scenario provides additional attack surface where malicious actors could potentially craft payloads to execute arbitrary code with kernel privileges, especially if the freed memory contains sensitive data structures or function pointers. These vulnerabilities affect all Android releases from Code Aurora Forum that utilize the Linux kernel, making them widespread across numerous devices including smartphones, tablets, and other mobile platforms. The attack vectors involve concurrent access to debugfs interfaces which can be triggered through various system processes or malicious applications that have appropriate permissions to interact with kernel debug interfaces.
Mitigation strategies for this vulnerability require implementing proper synchronization mechanisms to prevent concurrent access to the debugfs file controlling IPA IPC logging. Kernel developers should implement mutex locks or other atomic operations to ensure exclusive access when modifying the debugfs file and when destroying the IPC log contexts. The system should also include proper reference counting mechanisms to prevent premature deallocation of IPC log contexts during active logging operations. Additionally, input validation and bounds checking should be strengthened to prevent invalid writes to debugfs interfaces. System administrators and device manufacturers should ensure timely patching of affected kernel versions and consider implementing runtime monitoring to detect anomalous access patterns to debugfs interfaces. The vulnerability demonstrates the critical importance of proper concurrent programming practices in kernel space and aligns with ATT&CK technique T1068 which covers privilege escalation through kernel exploits, emphasizing the need for robust memory management and synchronization in operating system kernels.