Overview
CVE-2025-40253 describes a double-free vulnerability discovered and patched in the Linux kernel’s s390/ctcm (Channel-to-Channel communication) subsystem. This vulnerability could potentially lead to system instability or other unexpected behavior if exploited. The issue was identified by the clang static analyzer and has been addressed in recent kernel updates.
Technical Details
The vulnerability resides within the ctcmpc_unpack_skb function in the s390/ctcm subsystem. Specifically, the mpc_rcvd_sweep_req(mpcginfo) function, which is conditionally called from ctcmpc_unpack_skb, frees the mpcginfo structure. Subsequently, the ctcmpc_unpack_skb function contains a redundant kfree call that attempts to free the same mpcginfo structure a second time, leading to a double-free condition.
The problematic code sequence:
// ... inside ctcmpc_unpack_skb ...
if (condition) {
mpc_rcvd_sweep_req(mpcginfo); // Frees mpcginfo
}
kfree(mpcginfo); // Double-free!
// ...
CVSS Analysis
Currently, a CVSS score is not available for CVE-2025-40253. The severity is also marked as N/A. While a double-free vulnerability can be critical, the specific impact depends on the context and whether it can be reliably triggered and exploited. Given the lack of further details, it’s prudent to apply the available patch to mitigate potential risks.
Possible Impact
A double-free vulnerability can lead to the following potential impacts:
- System Instability: Corruption of kernel memory can cause unpredictable system behavior, including crashes.
- Denial of Service (DoS): A successful double-free exploit might lead to a kernel panic, resulting in a DoS condition.
- Potential for Code Execution: While less likely in this specific scenario (due to the static analysis detection), double-free vulnerabilities can sometimes be leveraged for more severe exploitation, such as arbitrary code execution, under specific conditions.
Mitigation or Patch Steps
The vulnerability has been addressed by removing the redundant kfree call in the mpc_rcvd_sweep_req(mpcginfo) function. To mitigate this vulnerability, users should apply the patch available in the upstream Linux kernel. This can be accomplished by upgrading to a kernel version that includes the fix or by applying the patch directly. Check with your Linux distribution vendor for specific update instructions.
References
Kernel Commit 1
Kernel Commit 2
Kernel Commit 3
Kernel Commit 4
Kernel Commit 5
