CVE-2023-52847 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
media: bttv: fix use after free error due to btv->timeout timer
There may be some a race condition between timer function bttv_irq_timeout and bttv_remove. The timer is setup in probe and there is no timer_delete operation in remove function. When it hit kfree btv, the function might still be invoked, which will cause use after free bug.
This bug is found by static analysis, it may be false positive.
Fix it by adding del_timer_sync invoking to the remove function.
cpu0 cpu1 bttv_probe ->timer_setup ->bttv_set_dma ->mod_timer; bttv_remove ->kfree(btv); ->bttv_irq_timeout ->USE btv
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability described in CVE-2023-52847 represents a critical use-after-free error within the Linux kernel's bttv ( Brooktree 464/465/466/467/468 video capture driver) subsystem. This flaw exists in the media framework's video capture drivers and stems from improper handling of the btv->timeout timer during device removal operations. The issue manifests as a race condition between the timer callback function bttv_irq_timeout and the device removal function bttv_remove, creating a scenario where memory deallocation occurs before all pending timer callbacks can complete execution.
The technical root cause of this vulnerability lies in the asynchronous nature of timer execution within the kernel's interrupt handling framework. During device probe operations, the bttv_probe function establishes a timer using timer_setup and subsequently modifies this timer through mod_timer calls during bttv_set_dma operations. However, when bttv_remove is executed to clean up device resources, it directly calls kfree(btv) without properly deleting the timer first. This sequence allows the timer callback function bttv_irq_timeout to execute against already freed memory, resulting in a use-after-free condition that can lead to memory corruption and potential privilege escalation.
This vulnerability directly maps to CWE-416, which describes the use of freed memory condition, and aligns with ATT&CK technique T1068, which involves the exploitation of privilege escalation vulnerabilities. The race condition described in the vulnerability analysis demonstrates a classic timing issue where concurrent execution paths in different CPU contexts create a window of opportunity for memory corruption. The static analysis approach used to identify this issue reflects modern security practices for detecting memory safety vulnerabilities in kernel code, though the authors note this could potentially be a false positive requiring further validation through dynamic analysis or fuzzing.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could enable an attacker to manipulate kernel memory structures and potentially escalate privileges to root access. The bttv driver is commonly used for video capture operations in various Linux systems, making this vulnerability exploitable in environments where video capture hardware is present. The fix implemented involves adding del_timer_sync() calls to the remove function, ensuring that all pending timer callbacks are properly synchronized and completed before memory deallocation occurs. This mitigation approach follows established kernel security best practices for preventing race conditions in concurrent systems and aligns with the principle of proper resource cleanup in device driver development.
The vulnerability highlights the complexity of kernel-level programming where multiple execution contexts must be carefully coordinated to prevent timing-related memory safety issues. The CPU0 and CPU1 execution flow demonstrates how concurrent operations can create dangerous race conditions, with the timer setup occurring in one context while memory deallocation happens in another. This scenario represents a common challenge in embedded systems and device driver development where hardware interrupts and software timers must be properly synchronized with resource management operations. The fix addresses the fundamental issue of missing timer cleanup in the device removal path, ensuring that all timer-related resources are properly reclaimed before device memory is freed, thereby preventing the use-after-free condition that could otherwise be exploited by malicious actors.