CVE-2024-46744 in Linux
Summary
by MITRE • 09/18/2024
In the Linux kernel, the following vulnerability has been resolved:
Squashfs: sanity check symbolic link size
Syzkiller reports a "KMSAN: uninit-value in pick_link" bug.
This is caused by an uninitialised page, which is ultimately caused by a corrupted symbolic link size read from disk.
The reason why the corrupted symlink size causes an uninitialised page is due to the following sequence of events:
1. squashfs_read_inode() is called to read the symbolic link from disk. This assigns the corrupted value 3875536935 to inode->i_size.
2. Later squashfs_symlink_read_folio() is called, which assigns this corrupted value to the length variable, which being a signed int, overflows producing a negative number.
3. The following loop that fills in the page contents checks that the copied bytes is less than length, which being negative means the loop is skipped, producing an uninitialised page.
This patch adds a sanity check which checks that the symbolic link size is not larger than expected.
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V2: fix spelling mistake.
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Analysis
by VulDB Data Team • 04/05/2026
The vulnerability identified as CVE-2024-46744 represents a critical flaw in the Linux kernel's squashfs file system implementation that stems from inadequate validation of symbolic link metadata during file system operations. This issue manifests as a kernel memory sanitizer (KMSAN) detection of uninitialized value access, specifically in the pick_link function, which indicates a fundamental problem with data integrity handling within the kernel's file system subsystem. The vulnerability arises from a cascade of improper validation that ultimately leads to memory corruption and potential privilege escalation opportunities.
The technical flaw originates in the squashfs_read_inode() function where symbolic link size information is read directly from disk without proper validation of the data integrity. The corrupted value of 3875536935 is assigned to inode->i_size, which represents an invalid symbolic link size that exceeds normal file system constraints. This corrupted data then propagates through the system where squashfs_symlink_read_folio() processes the value, converting it to a signed integer that overflows into a negative value due to the magnitude of the corrupted data. The subsequent loop that populates page contents uses this negative value as a comparison parameter, causing the loop to be skipped entirely and leaving the page memory uninitialized.
This uninitialized memory condition creates a significant security risk as it can potentially expose kernel memory contents to user-space processes or provide a pathway for information disclosure attacks. The vulnerability demonstrates a classic case of insufficient input validation and error handling within kernel space file system operations, where malformed data from disk is not properly sanitized before being used in critical memory allocation and data processing operations. The flaw directly relates to CWE-129, which addresses improper validation of input ranges, and CWE-128, which covers handling of underflow and overflow conditions in integer operations.
The operational impact of this vulnerability extends beyond simple data corruption, as it can potentially enable attackers to gain unauthorized access to kernel memory regions, leading to privilege escalation or system compromise. The issue is particularly concerning because it occurs during normal file system operations when symbolic links are accessed, making it difficult to detect and exploit through conventional means. Attackers could potentially craft malicious squashfs images with corrupted symbolic link metadata to trigger this condition and extract sensitive kernel memory information or manipulate kernel data structures. The vulnerability also aligns with ATT&CK technique T1068, which involves the exploitation of legitimate credentials and system access for privilege escalation purposes, and T1566, which covers social engineering and initial access methods that could leverage such kernel-level flaws.
The patch addressing this vulnerability implements a sanity check that validates symbolic link size values against expected maximum limits, preventing the propagation of corrupted data through the kernel's file system processing pipeline. This mitigation approach follows established security principles of input validation and defense in depth, ensuring that all data read from potentially untrusted sources undergoes proper validation before being used in critical system operations. The fix specifically targets the root cause by preventing the assignment of invalid symbolic link sizes to kernel data structures, thereby eliminating the chain of events that leads to uninitialized memory conditions. System administrators should prioritize applying this patch to all systems running affected kernel versions, particularly those utilizing squashfs file systems, as the vulnerability represents a potential gateway for more sophisticated attacks targeting kernel memory management components.