CVE-2026-92494 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix buffer_head leak in ext4_init_orphan_info
ext4_init_orphan_info() reads orphan file blocks with ext4_bread() and stores the returned buffer_head in oi->of_binfo[i].ob_bh.
If ext4_bread() succeeds but the orphan block magic or checksum validation fails, the function jumps to out_free. However, the old out_free loop starts releasing buffers from i - 1, so the current buffer_head at index i is skipped.
This leaks the buffer_head reference obtained by ext4_bread() on the bad magic and bad checksum error paths.
Fix this by tracking the number of successfully read buffer_heads and releasing exactly those buffer_heads on the error path.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's ext4 filesystem driver involves a resource leak within the ext4_init_orphan_info function, specifically concerning the management of buffer_head structures. This function is responsible for initializing orphan inode information by reading blocks associated with an orphan file. During this process, it utilizes the ext4_bread helper to read these blocks from disk and stores the resulting buffer_head pointers in a dedicated array within the orphan info structure. The core technical flaw arises during error handling when validation of the block's magic number or checksum fails after a successful read operation. In such scenarios, the code path jumps to an exit label designed for cleanup, but this existing cleanup logic incorrectly iterates through previously allocated buffer heads starting from index i minus one, thereby skipping the release of the current buffer head at index i that was just acquired and found to be invalid.
This oversight results in a persistent memory leak where reference counts on kernel objects are not properly decremented upon failure conditions. In the context of Linux kernel development, buffer_head structures represent cached disk blocks and hold critical references to underlying page cache pages. Failure to release these references means that the associated physical memory cannot be reclaimed or reused by other subsystems until the system is rebooted or the specific filesystem instance is unmounted. While a single occurrence might seem negligible, repeated triggers of this error path during normal filesystem operations can lead to gradual depletion of available kernel memory resources. This type of flaw falls under CWE-401, which describes missing release of memory after effective allocation, and represents a classic example of improper resource management in low-level system software where explicit cleanup logic must precisely mirror the acquisition sequence.
The operational impact of this vulnerability is primarily related to long-term system stability rather than immediate security compromise or privilege escalation. Since the issue involves leaking kernel memory references without exposing sensitive data or allowing arbitrary code execution, it does not directly facilitate attacks such as remote code execution or local privilege elevation. However, over time, these accumulated leaks can contribute to increased pressure on the kernel's slab allocator and page cache management subsystems. In environments with high rates of filesystem corruption detection or frequent mounting and unmounting operations involving damaged ext4 volumes, this leak could exacerbate memory fragmentation or eventually lead to out-of-memory conditions that degrade system performance or cause service interruptions for critical applications relying on stable resource availability.
Mitigation strategies focus primarily on applying the upstream kernel patch that corrects the loop logic within ext4_init_orphan_info. The fix involves introducing a counter to track exactly how many buffer heads have been successfully allocated and ensuring that the error handling path releases only those specific buffers rather than skipping the most recent one. System administrators should ensure their systems are updated with the latest stable kernel versions containing this patch, as it directly addresses the root cause of the resource leak without requiring changes to application logic or user behavior. Additionally, monitoring tools that track slab allocator usage and memory leaks in long-running kernels can help identify if similar patterns exist elsewhere in the codebase, although no immediate workarounds are necessary beyond applying the vendor-provided security update for affected distributions.