CVE-2026-99067 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
btrfs: scrub: fix local_root reference leak in scrub_print_warning_inode()
When paths_from_inode() fails, scrub_print_warning_inode() jumps to err without dropping the reference taken by btrfs_get_fs_root(), leaking a reference to the root every time path resolution fails while printing scrub warnings. Every other error and success path of the function drops the reference.
Drop the reference on the paths_from_inode() failure path too.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel's Btrfs filesystem implementation contains a resource management flaw within its data scrubbing subsystem, specifically in the scrub_print_warning_inode function. This vulnerability manifests as a local root reference leak that occurs during error handling routines when resolving file system paths fails. The issue stems from an asymmetry in how references to btrfs_fs_root structures are managed across different execution paths of the same function. When the kernel performs a disk scrub operation, it frequently needs to access metadata and inode information for files located on corrupted or inconsistent sectors. To facilitate this, the code invokes btrfs_get_fs_root() which increments a reference count on the root object to ensure its validity during subsequent operations. This is standard practice in Linux kernel development to prevent use-after-free conditions where an object might be deallocated while still being accessed by active processes.
The technical flaw arises specifically when the paths_from_inode function, responsible for translating inode data into usable path structures required for detailed warning messages, encounters a failure condition. In this scenario, control flow jumps to an error label designated as err. However, unlike every other success and error branch within scrub_print_warning_inode(), which correctly decrements the reference count via btrfs_put_root() or similar cleanup mechanisms, the paths_from_inode failure path neglects to release the previously acquired root reference. This omission means that for each instance where a warning cannot be fully printed due to path resolution issues, one reference count remains permanently incremented without corresponding deallocation logic. Over time, particularly on file systems with significant corruption requiring extensive scrubbing and repeated warnings, this leads to an accumulation of unreleased references.
From an operational impact perspective, this vulnerability primarily results in memory leaks within the kernel space rather than immediate system crashes or privilege escalation vectors. The persistent incrementing of reference counts prevents the btrfs_fs_root structures from being freed even when they are no longer needed by other subsystems. As these leaked objects accumulate, they consume increasing amounts of non-swappable kernel memory. In environments where Btrfs is subjected to heavy scrubbing operations due to hardware errors or file system inconsistencies, this leak can accelerate towards exhausting available kernel memory resources. While the immediate risk may appear low for typical desktop usage patterns involving occasional checks, servers with large-scale storage arrays experiencing frequent I/O errors could see degraded performance or eventual out-of-memory conditions affecting critical services running on the host system.
This vulnerability aligns closely with CWE-401, which describes a missing release of memory after effective use, and falls under the broader category of resource leaks that compromise long-term system stability rather than providing direct exploitation pathways for attackers. It does not directly map to specific MITRE ATT&CK techniques as it is an internal kernel logic error rather than an external attack vector, though its effects contribute to Denial of Service scenarios by degrading system resources over extended periods. The root cause lies in incomplete exception handling logic where developers failed to maintain symmetry between resource acquisition and release across all conditional branches within the function scope.
Mitigation strategies for this issue involve applying the upstream kernel patch that corrects the control flow in scrub_print_warning_inode(). Administrators managing Btrfs file systems should ensure their kernels are updated to versions containing this fix, which explicitly adds a call to drop the reference on the paths_from_inode failure path. Until such updates are deployed, monitoring system memory usage and dmesg logs for signs of kernel memory pressure during scrubbing operations can help identify affected environments. Regular maintenance of file systems with tools like btrfs check and scrub is recommended, but operators should be aware that running these utilities on severely corrupted volumes without patched kernels may inadvertently contribute to resource exhaustion over time.