CVE-2025-38688 in Linux
Summary
by MITRE • 09/04/2025
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Prevent ALIGN() overflow
When allocating IOVA the candidate range gets aligned to the target alignment. If the range is close to ULONG_MAX then the ALIGN() can wrap resulting in a corrupted iova.
Open code the ALIGN() using get_add_overflow() to prevent this. This simplifies the checks as we don't need to check for length earlier either.
Consolidate the two copies of this code under a single helper.
This bug would allow userspace to create a mapping that overlaps with some other mapping or a reserved range.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability identified as CVE-2025-38688 resides within the Linux kernel's iommufd subsystem, specifically addressing a critical flaw in IOVA (I/O Virtual Address) range allocation mechanisms. This issue manifests when the kernel attempts to align IOVA candidate ranges to specified alignment boundaries during memory mapping operations. The fundamental problem occurs when dealing with ranges that approach the maximum value representable by the ULONG data type, where the standard ALIGN() macro implementation fails due to integer overflow conditions. The vulnerability represents a classic case of improper input validation and arithmetic overflow handling that can lead to memory corruption and potential privilege escalation scenarios.
The technical implementation flaw stems from the use of the ALIGN() macro without proper overflow checking mechanisms. When the kernel processes IOVA allocation requests, it calculates aligned ranges by applying alignment boundaries to candidate memory regions. However, when these candidate ranges are positioned near ULONG_MAX, the alignment calculation causes integer wraparound behavior that corrupts the IOVA tracking structures. This overflow condition creates a scenario where the system's memory management becomes inconsistent, potentially allowing malicious userspace processes to manipulate memory mappings in unintended ways. The vulnerability directly maps to CWE-191, which deals with integer underflow or overflow conditions, and specifically addresses improper integer handling in kernel memory management operations.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables userspace attackers to create overlapping memory mappings that can interfere with legitimate system operations. When the ALIGN() overflow occurs, it results in corrupted IOVA structures that may cause mappings to overlap with existing valid mappings or reserved memory regions. This overlap condition can lead to data corruption, privilege escalation, and potentially system instability. The vulnerability essentially allows an unprivileged user to manipulate kernel memory management data structures, creating opportunities for information disclosure, denial of service, or more severe compromise scenarios. From an ATT&CK perspective, this vulnerability aligns with techniques involving privilege escalation and memory corruption, specifically targeting the kernel's memory management subsystem.
The resolution implemented for CVE-2025-38688 involves replacing the problematic ALIGN() macro with an open-coded implementation that explicitly uses get_add_overflow() checks to prevent the overflow condition. This approach eliminates the need for separate length validation checks and consolidates duplicate code implementations into a single helper function. The fix addresses the root cause by ensuring that alignment calculations properly handle boundary conditions near ULONG_MAX, thereby preventing the wraparound behavior that led to corruption. This mitigation strategy follows established kernel security practices for integer overflow prevention and demonstrates proper defensive programming techniques. The consolidated helper function reduces code duplication while providing more robust overflow protection, aligning with security best practices for kernel development and maintenance. The fix ensures that IOVA allocation operations remain within safe boundaries and prevents the corruption of memory management data structures that could otherwise be exploited by malicious actors.