CVE-2026-68450 in Linux
Summary
by MITRE • 08/12/2026
In the Linux kernel, the following vulnerability has been resolved:
btrfs: free mapping node on duplicate reloc root insert
__add_reloc_root() allocates a mapping_node before inserting it into rc->reloc_root_tree. If rb_simple_insert() finds an existing entry, it returns the existing rb_node and leaves the newly allocated node unlinked.
The error path then returns -EEXIST without freeing the new node. Since the node was never inserted into reloc_root_tree, the later cleanup in put_reloc_control() cannot find it either.
Free the newly allocated node before returning -EEXIST.
The callers currently assert that -EEXIST should not happen, so this is a defensive cleanup for an unexpected duplicate insert path. If the path is ever reached, the local allocation should still be released.
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Analysis
by VulDB Data Team • 08/12/2026
This vulnerability exists within the btrfs file system implementation in the Linux kernel where a memory leak occurs during relocation root management operations. The issue manifests in the __add_reloc_root() function which handles the allocation and insertion of mapping nodes into the relocation root tree structure. When rb_simple_insert() encounters an existing entry with identical keys, it returns the existing node rather than inserting the new one, leaving the newly allocated mapping_node unlinked and unreferenced. This particular memory management flaw represents a classic resource leak scenario where allocated kernel memory is not properly deallocated.
The technical execution path begins with __add_reloc_root() allocating a new mapping_node structure through standard kernel memory allocation mechanisms, followed by an attempt to insert this node into the rc->reloc_root_tree data structure. When duplicate insertion occurs, the rb_simple_insert() function detects the existing entry and returns control without performing the actual insertion operation. However, the error handling code path that executes upon encountering -EEXIST fails to release the newly allocated memory resource, creating a memory leak that persists until the entire relocation control structure is cleaned up.
The operational impact of this vulnerability extends beyond simple memory consumption as it represents a potential denial of service vector within storage subsystems utilizing btrfs file systems. While the callers of this function currently assert that -EEXIST should never occur, making this a defensive measure against unexpected code paths, the presence of such leaks in kernel space can accumulate over time and lead to system instability. The vulnerability directly relates to CWE-401 which categorizes improper handling of memory allocation failures, specifically addressing the lack of proper resource deallocation in error conditions.
The mitigation strategy involves implementing proper cleanup logic before returning -EEXIST error codes, ensuring that any newly allocated mapping_node structures are freed immediately upon detection of duplicate insertion attempts. This defensive programming approach aligns with best practices for kernel development and follows ATT&CK technique T1490 which addresses resource exhaustion through memory leaks in operating system components. The fix requires minimal code changes but provides significant protection against potential exploitation scenarios where repeated allocation failures could lead to system memory exhaustion.
This vulnerability demonstrates the critical importance of proper resource management in kernel space operations, where even seemingly minor oversight in error path handling can create persistent memory leaks. The btrfs implementation's failure to account for all possible execution paths during node insertion creates a scenario where allocated kernel memory becomes orphaned and unrecoverable, representing a fundamental flaw in the resource lifecycle management approach. Such issues are particularly dangerous in storage subsystems where repeated operations on large data sets could amplify the memory leak effects over time.
The fix addresses the root cause by ensuring that allocation occurs only when insertion will actually happen, or by properly cleaning up allocations when insertion is prevented due to duplicates. This approach maintains consistency with Linux kernel memory management principles and prevents potential escalation of resource exhaustion conditions. The solution also reinforces proper adherence to kernel development practices where all allocated resources must eventually be freed regardless of the execution path taken during error handling scenarios.
This vulnerability highlights the necessity of comprehensive testing for edge cases in storage system implementations, particularly when dealing with tree-based data structures that may encounter duplicate key scenarios during insertion operations. The defensive nature of this fix indicates that while the condition was not expected to occur in normal operation, proper error handling should account for all possible code paths to prevent resource leaks and maintain system stability. The implementation follows established patterns for kernel memory management and demonstrates the importance of considering all potential execution flows when developing critical file system components.