CVE-2026-97415 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
btrfs: tree-checker: validate names in ROOT_REF and ROOT_BACKREF
ROOT_REF and ROOT_BACKREF items contain a struct btrfs_root_ref followed by the subvolume name. Several readers assume that this layout is already valid and then use the on-disk name length directly. A corrupted item can therefore make those readers address bytes outside the item, and BTRFS_IOC_GET_SUBVOL_INFO can copy too many bytes into its fixed-size UAPI name buffer.
Validate ROOT_REF and ROOT_BACKREF items in tree-checker before any reader uses them. Reject records that do not contain a non-empty name, whose name_len does not exactly describe the remaining item payload, or whose name exceeds BTRFS_NAME_LEN.
For BTRFS_IOC_GET_SUBVOL_INFO, copy only the validated on-disk name_len instead of deriving the copy length from the item size. The ioctl result is zeroed when allocated. That leaves the existing trailing zero byte untouched.
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Analysis
by VulDB Data Team • 09/24/2026
The vulnerability identified in the Linux kernel's btrfs filesystem driver centers on insufficient validation of metadata structures within the tree-checker component, specifically concerning ROOT_REF and ROOT_BACKREF items. These data structures are fundamental to BTRFS subvolume management, containing a struct btrfs_root_ref followed by the actual name of the subvolume. Historically, various readers within the kernel assumed that these on-disk layouts were inherently valid and proceeded to use the length field directly from the disk structure without independent verification. This assumption creates a critical security gap because if an attacker can corrupt or manipulate the metadata stored on the filesystem, they can craft items where the declared name length does not match the actual remaining payload of the item. Consequently, readers that rely on this untrusted length value may attempt to access memory addresses outside the bounds of the allocated buffer associated with the item.
This out-of-bounds read condition represents a significant risk as it allows for potential information disclosure or kernel instability depending on what data resides in the adjacent memory regions. The vulnerability is particularly exploitable through the BTRFS_IOC_GET_SUBVOL_INFO ioctl interface, which interacts directly with user-space applications to retrieve subvolume information. When this ioctl processes a corrupted ROOT_REF or ROOT_BACKREF item, it may copy an excessive number of bytes into its fixed-size User API name buffer based on the maliciously inflated length field found in the metadata. This behavior constitutes a classic out-of-bounds write scenario if the copied data exceeds the destination buffer size, potentially leading to memory corruption, privilege escalation, or system crashes. The root cause is categorized under CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write, reflecting the failure to validate input boundaries before performing memory operations.
The operational impact of this flaw extends beyond simple data leakage. By exploiting the lack of validation in the tree-checker, a local attacker with access to modify filesystem metadata could trigger these out-of-bounds accesses during routine administrative tasks or automated monitoring processes that query subvolume details. This aligns with ATT&CK technique T1059 Command and Scripting Interpreter if used as part of a broader exploitation chain involving script execution, although the primary vector is local privilege escalation via memory corruption. The ability to corrupt kernel memory through filesystem operations highlights the importance of treating all on-disk data as untrusted until explicitly validated by the kernel's integrity checks.
To mitigate this vulnerability, the Linux kernel developers have implemented strict validation logic within the tree-checker module before any reader attempts to utilize ROOT_REF or BACKREF items. The updated code now rejects records that fail specific sanity checks: it ensures the name field is not empty, verifies that the declared name_len exactly matches the remaining payload size of the item, and confirms that the name length does not exceed BTRFS_NAME_LEN, which defines the maximum allowable filename length in BTRFS. This proactive validation prevents malformed structures from propagating to higher-level functions that assume valid input data integrity.
Furthermore, specific adjustments were made to the handling of the BTRFS_IOC_GET_SUBVOL_INFO ioctl call. Instead of deriving the copy length from the total item size or relying on potentially corrupted metadata fields, the code now copies only the validated name_len value into the user-space buffer. This change ensures that the amount of data transferred is strictly bounded by previously verified constraints rather than untrusted disk values. Additionally, since the ioctl result area is zeroed upon allocation, any trailing bytes beyond the copied valid name remain null-terminated and untouched, preserving string integrity for applications expecting standard C-style strings. These measures collectively close the gap between on-disk metadata representation and in-memory processing, ensuring that filesystem operations remain robust against corrupted or maliciously crafted disk images.