CVE-2021-47535 in Linux
Summary
by MITRE • 05/24/2024
In the Linux kernel, the following vulnerability has been resolved:
drm/msm/a6xx: Allocate enough space for GMU registers
In commit 142639a52a01 ("drm/msm/a6xx: fix crashstate capture for A650") we changed a6xx_get_gmu_registers() to read 3 sets of registers. Unfortunately, we didn't change the memory allocation for the array. That leads to a KASAN warning (this was on the chromeos-5.4 kernel, which has the problematic commit backported to it):
BUG: KASAN: slab-out-of-bounds in _a6xx_get_gmu_registers+0x144/0x430 Write of size 8 at addr ffffff80c89432b0 by task A618-worker/209 CPU: 5 PID: 209 Comm: A618-worker Tainted: G W 5.4.156-lockdep #22 Hardware name: Google Lazor Limozeen without Touchscreen (rev5 - rev8) (DT) Call trace: dump_backtrace+0x0/0x248 show_stack+0x20/0x2c dump_stack+0x128/0x1ec print_address_description+0x88/0x4a0 __kasan_report+0xfc/0x120 kasan_report+0x10/0x18 __asan_report_store8_noabort+0x1c/0x24 _a6xx_get_gmu_registers+0x144/0x430 a6xx_gpu_state_get+0x330/0x25d4 msm_gpu_crashstate_capture+0xa0/0x84c recover_worker+0x328/0x838 kthread_worker_fn+0x32c/0x574 kthread+0x2dc/0x39c ret_from_fork+0x10/0x18
Allocated by task 209: __kasan_kmalloc+0xfc/0x1c4 kasan_kmalloc+0xc/0x14 kmem_cache_alloc_trace+0x1f0/0x2a0 a6xx_gpu_state_get+0x164/0x25d4 msm_gpu_crashstate_capture+0xa0/0x84c recover_worker+0x328/0x838 kthread_worker_fn+0x32c/0x574 kthread+0x2dc/0x39c ret_from_fork+0x10/0x18
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Analysis
by VulDB Data Team • 12/04/2024
The vulnerability described in CVE-2021-47535 represents a memory allocation flaw within the Linux kernel's graphics driver subsystem, specifically affecting the Qualcomm Snapdragon 6xx series GPU drivers. This issue manifests in the drm/msm/a6xx driver component where the kernel attempts to capture GPU crash state information, particularly for the A650 GPU variant. The problem stems from a mismatch between the number of register sets that the code attempts to read and the memory allocation that was previously established for storing these registers. The root cause lies in commit 142639a52a01 which modified the a6xx_get_gmu_registers function to handle three distinct sets of registers but failed to adjust the corresponding memory allocation for the array that stores these register values. This oversight creates a scenario where the kernel attempts to write data beyond the allocated memory boundaries, triggering a KASAN (Kernel Address Sanitizer) warning that indicates a slab-out-of-bounds memory access error. The vulnerability specifically impacts systems running the chromeos-5.4 kernel version where this problematic commit was backported, making it particularly relevant to Chromebook devices utilizing Qualcomm GPU hardware.
The technical flaw in this vulnerability can be categorized under CWE-129, which represents an Improper Validation of Array Index, and more specifically relates to improper memory allocation handling within kernel space. The error occurs during the gpu crashstate capture process when the system attempts to gather diagnostic information from the GPU's GMU (Graphics Management Unit) registers. The memory allocation for the register array was not updated to accommodate the increased number of register sets from one to three, resulting in a buffer overflow condition. When the kernel's recovery worker thread executes the a6xx_get_gmu_registers function, it attempts to write 8-byte values to memory locations that extend beyond the originally allocated buffer space, causing the kernel to detect this as a memory safety violation. The KASAN warning specifically identifies the fault location at _a6xx_get_gmu_registers function where the out-of-bounds write occurs, with the memory address ff80c89432b0 indicating the specific location where the violation happened. This type of memory corruption can potentially lead to system instability, crashes, or even provide an avenue for privilege escalation attacks if exploited properly.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise the stability and security of devices running affected kernel versions. When the GPU crashstate capture mechanism is triggered during system recovery operations, the out-of-bounds memory access can cause the kernel to panic or crash, leading to service disruption on Chromebook devices and other systems using Qualcomm's A6xx GPU architecture. The vulnerability affects the msm_gpu_crashstate_capture function which is part of the broader GPU recovery infrastructure, meaning that any GPU-related error conditions that trigger this code path could potentially cause system instability. From an attacker perspective, this memory corruption vulnerability could potentially be leveraged to achieve privilege escalation or denial of service attacks, especially if the system is running in an environment where GPU operations are frequently accessed or if the crashstate capture mechanism is triggered under specific conditions. The vulnerability affects systems using the chromeos-5.4 kernel specifically, but given the nature of kernel-level memory management issues, similar patterns could potentially exist in other kernel versions or driver implementations that have not been properly updated.
Mitigation strategies for this vulnerability should focus on ensuring proper memory allocation alignment with the actual data requirements and implementing robust code review processes for kernel modifications. The primary fix involves updating the memory allocation logic in the a6xx_gpu_state_get function to properly account for the three register sets that the code now attempts to read, ensuring that the allocated buffer size accommodates the increased data requirements. System administrators should prioritize applying kernel updates that include the fix for this vulnerability, particularly those that address the specific commit 142639a52a01 and its associated memory allocation changes. Regular kernel security audits should be conducted to identify similar memory allocation mismatches in other driver components, as the underlying issue of insufficient buffer sizing for increased data requirements is a common pattern in kernel security vulnerabilities. Additionally, implementing proper bounds checking and memory validation mechanisms in kernel space operations can help prevent similar issues from occurring in the future. The vulnerability also highlights the importance of maintaining proper testing procedures for backported kernel patches, as the issue was present in the chromeos-5.4 kernel where the problematic commit was backported, indicating that proper regression testing should be performed when applying patches to long-term support kernel versions.