CVE-2026-97485 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
omfs: handle set_blocksize failures
omfs uses buffer_heads, which don't handle block size > PAGE_SIZE well. Without this, mounting we will hit the
BUG_ON(offset >= folio_size(folio));
in folio_set_bh on the first __bread_gfp call.
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Analysis
by VulDB Data Team • 09/24/2026
The Open-Minded File System (OMFS) implementation within the Linux kernel contains a critical flaw related to block size handling during file system mounting operations. This vulnerability stems from an inadequate check for set_blocksize failures, which leads to improper initialization of buffer heads when the underlying storage device or image presents a block size that exceeds the standard PAGE_SIZE limit. In modern Linux kernels, memory management is heavily reliant on folios and buffer heads to manage data caching and I/O operations efficiently. The OMFS driver fails to validate whether the requested block size is compatible with these internal structures before proceeding with mount procedures, creating a scenario where subsequent kernel functions encounter unexpected state mismatches.
The technical root cause lies in the interaction between the file system's mounting logic and the core VFS layer's buffer head management routines. When OMFS attempts to read metadata or data blocks using __bread_gfp, it relies on folio_set_bh to associate a buffer head with a specific memory folio. However, this function contains an assertion that ensures the offset of the block does not exceed the size of the folio itself. Because OMFS did not properly handle cases where set_blocksize resulted in a configuration incompatible with PAGE_SIZE limits, the resulting offsets calculated for these blocks often exceeded the allocated folio sizes. This discrepancy triggers the BUG_ON macro embedded within folio_set_bh, causing an immediate kernel panic rather than returning a graceful error code to the user space application attempting to mount the file system.
From an operational perspective, this vulnerability results in a denial of service condition specifically targeting local users or automated scripts that attempt to access OMFS formatted volumes with non-standard block sizes. The impact is severe as it causes the entire kernel instance to crash via a BUG_ON assertion failure, requiring a hard reset of the affected system. This lack of robust error handling means that any external storage device or disk image utilizing an OMFS partition with a block size larger than what the current memory management subsystem expects will destabilize the host operating system upon access attempts. The flaw highlights a broader issue in legacy file system drivers where assumptions about hardware capabilities are not sufficiently validated against modern kernel constraints.
To mitigate this risk, it is essential to apply upstream Linux kernel patches that introduce proper validation checks for block size compatibility before initializing buffer heads. System administrators should ensure their kernels are updated with the latest fixes addressing OMFS stability issues. Furthermore, when working with legacy file systems like OMFS in virtualized or containerized environments, it is advisable to standardize disk images and storage configurations to use block sizes that align with PAGE_SIZE limits unless specific kernel modifications have been applied to support larger blocks safely. Monitoring for similar patterns of unchecked assumptions about hardware parameters in other legacy drivers can also help prevent analogous stability issues across the system infrastructure. This incident underscores the importance of rigorous input validation at the boundary between file system implementations and core memory management subsystems, ensuring that unexpected configurations are handled gracefully rather than triggering fatal assertions.