CVE-2024-26884 in Linux
Summary
by MITRE • 04/17/2024
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix hashtab overflow check on 32-bit arches
The hashtab code relies on roundup_pow_of_two() to compute the number of hash buckets, and contains an overflow check by checking if the resulting value is 0. However, on 32-bit arches, the roundup code itself can overflow by doing a 32-bit left-shift of an unsigned long value, which is undefined behaviour, so it is not guaranteed to truncate neatly. This was triggered by syzbot on the DEVMAP_HASH type, which contains the same check, copied from the hashtab code. So apply the same fix to hashtab, by moving the overflow check to before the roundup.
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability CVE-2024-26884 resides within the Linux kernel's BPF (Berkeley Packet Filter) subsystem, specifically affecting the hashtab implementation on 32-bit architectures. This issue demonstrates a critical flaw in memory management and arithmetic operations that could potentially lead to system instability or security compromises. The vulnerability impacts the kernel's ability to properly handle hash table operations when dealing with large data structures, particularly in environments where 32-bit addressing limitations become significant. The problem manifests through improper overflow checking mechanisms that fail to account for architecture-specific behaviors in unsigned integer arithmetic.
The technical root cause stems from the use of the roundup_pow_of_two() function within the hash table implementation, which performs a 32-bit left-shift operation on unsigned long values. This operation creates undefined behavior on 32-bit systems where the shift operation may not truncate as expected, leading to unpredictable results in the hash bucket calculation. The existing overflow check that simply verifies if the result equals zero proves insufficient because it does not account for the intermediate overflow that occurs during the rounding calculation process. This flaw is particularly concerning as it affects the fundamental data structure management within the kernel's networking and security subsystems.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially allowing for privilege escalation or denial of service conditions within kernel space. When syzbot detected this issue in the DEVMAP_HASH type implementation, it highlighted the widespread nature of the problem since the same flawed code pattern was copied between different hash table implementations. The vulnerability affects systems running 32-bit kernels where BPF programs utilize hash tables for packet filtering, network monitoring, or other kernel-level operations. Attackers could potentially exploit this by crafting malicious BPF programs that trigger the overflow condition, leading to kernel memory corruption or system crashes.
The fix implemented addresses the core issue by repositioning the overflow check to occur before the roundup operation, ensuring that any potential overflow in the intermediate calculation is detected early in the process. This approach aligns with defensive programming principles and follows established security practices for handling arithmetic operations in kernel space. The solution prevents the undefined behavior that occurs during 32-bit left-shift operations on unsigned long values, thereby maintaining the integrity of hash table creation and management. This remediation approach is consistent with common security practices outlined in the CWE (Common Weakness Enumeration) catalog under weakness category 191, which deals with integer overflow or wraparound issues.
From an ATT&CK framework perspective, this vulnerability could be leveraged as part of privilege escalation techniques within the kernel domain, potentially enabling adversaries to gain elevated system privileges or disrupt critical kernel services. The fix represents a defensive measure against potential exploitation through kernel memory corruption attacks, aligning with techniques that focus on preventing information disclosure and system instability. The vulnerability's classification as a kernel-level integer overflow issue places it within the broader category of system integrity threats that can affect multiple attack vectors including those targeting kernel memory management, process isolation, and system resource control. This remediation ensures that hash table operations maintain predictable behavior across different architectural platforms while preserving the intended functionality of the BPF subsystem.