Linux Kernel cgroup v1 memory.soft_limit_in_bytes logic flaw triggers BUG() kernel crash fix

Vulnerability Overview Submission Title: Vulnerability/Issue Description: This commit aims to render the interface in cgroup v1 inert. Background: The v1 soft limit has been deprecated since kernel version 5.12, and no issues related to dependencies on this feature have been reported. Risk: The interface contains logical flaws that can lead to kernel crashes ( ). Specific Mechanism: The interface allows user space to trigger memory reclaim for a specific memory cgroup (memcg) via . This is the only path that triggers , which issues a warning under specific conditions. Remediation Strategy: The interface definition is retained to maintain backward compatibility, but write operations are ignored (always returning the maximum value), and the code paths triggering the kernel crash are removed. Impact Scope Affected Components: Linux Kernel Memory Management subsystem, specifically the cgroup v1 memory controller. Affected Files: Affected Versions: Kernel versions that include the cgroup v1 soft limit implementation and do not have this patch applied (primarily versions from v5.12 onwards, until this patch is merged). Remediation This patch modifies the code logic to make read-only or ineffective, with specific changes as follows: 1. Documentation Update ( ): Explicitly marks as deprecated. States that the interface is no longer available and should not be used. Removes detailed documentation on how the soft limit works, retaining only compatibility notes. 2. Code Modifications ( ): Removal of Call: In the function, the assertion that was triggered when exceeds is removed. Ignored Write Operations: The function is modified to no longer update the value actually; instead, it directly returns the number of bytes written (simulating success) and prints a warning indicating the feature is deprecated. Removal of Related Logic: In functions such as and , handling logic related to is removed or commented out to ensure read/write operations no longer affect kernel state. Key Code Changes (Extracted from Screenshots) 1. Removal of BUG() Assertion and Ignoring Writes (mm/memcontrol-v1.c) 2. Removal of RES_SOFT_LIMIT Handling Logic (mm/memcontrol-v1.c) 3. File Operations Structure Modification (mm/memcontrol-v1.c) Note: The core of this patch is defensive programming**. By removing dangerous code paths ( ) and disabling the functionality (ignoring writes), it prevents user space from triggering kernel crashes, while keeping the interface present to remain compatible with legacy user space tools.

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Linux Kernel cgroup v1 memory.soft_limit_in_bytes logic flaw triggers BUG() kernel crash fix