Overview
A newly discovered vulnerability in the Linux kernel, CVE-2022-49753, concerns the DMA engine and may potentially lead to system compromise or data leakage if exploited. As the Linux kernel powers a vast variety of systems and devices worldwide, this vulnerability is significant and requires immediate attention. The flaw lies in the double increment of client_count in dma_chan_get(), which can lead to inappropriate freeing of channel resources.
Vulnerability Summary
CVE ID: CVE-2022-49753
Severity: High (7.8 CVSS Score)
Attack Vector: Local
Privileges Required: Low
User Interaction: None
Impact: System compromise or data leakage
Affected Products
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Product | Affected Versions
Linux Kernel | 5.14.0-185.el9.x86_64 and earlier versions
How the Exploit Works
The vulnerability is located in the dmaengine subsystem of the Linux kernel. The dma_chan_get() function is responsible for handling DMA (Direct Memory Access) operations. When this function is called, it incorrectly increments the “client_count” twice for public channels. This can lead to an underflow of the reference count of the DMA channel.
As a result, the system mistakenly thinks that there are still clients using the channel when in fact, there are none. This can lead to the DMA channel’s resources not being freed when they should be, resulting in potential use-after-free scenarios.
Conceptual Example Code
While the exploit would require specific knowledge of the target system’s configuration and would be executed at the kernel level, it might conceptually look something like this:
#include <linux/dmaengine.h>
void exploit_dma_vulnerability(void) {
struct dma_chan *chan;
// Obtain a reference to a public DMA channel.
chan = dma_find_channel(DMA_MEMCPY);
// Call dma_chan_get() twice, incorrectly incrementing client count.
dma_chan_get(chan);
dma_chan_get(chan);
// System now believes there are more clients using the channel than there are.
// This can later result in a use-after-free situation when the channel's resources are not freed when they should be.
}Please note that this is a conceptual example and does not represent a usable exploit. It is provided for educational purposes only to help understand the nature of the vulnerability.