CVE-2026-46268 in Linux
Summary
by MITRE • 06/03/2026
In the Linux kernel, the following vulnerability has been resolved:
PCI/P2PDMA: Fix p2pmem_alloc_mmap() warning condition
Commit b7e282378773 has already changed the initial page refcount of p2pdma page from one to zero, however, in p2pmem_alloc_mmap() it uses "VM_WARN_ON_ONCE_PAGE(!page_ref_count(page))" to assert the initial page refcount should not be zero and the following will be reported when CONFIG_DEBUG_VM is enabled:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x380400000 flags: 0x20000000002000(reserved|node=0|zone=4) raw: 0020000000002000 ff1100015e3ab440 0000000000000000 0000000000000000 raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: VM_WARN_ON_ONCE_PAGE(!page_ref_count(page)) ------------[ cut here ]------------
WARNING: CPU: 5 PID: 449 at drivers/pci/p2pdma.c:240 p2pmem_alloc_mmap+0x83a/0xa60
Fix by using "page_ref_count(page)" as the assertion condition.
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Analysis
by VulDB Data Team • 06/03/2026
The vulnerability resides in the Linux kernel's PCI P2PDMA subsystem, specifically within the p2pmem_alloc_mmap() function that handles memory mapping operations for peer-to-peer direct memory access. This issue demonstrates a critical inconsistency in page reference counting logic that can trigger kernel warnings and potentially compromise system stability. The problem emerged from a previous commit that correctly adjusted the initial page reference count of p2pdma pages from one to zero, but failed to update the corresponding assertion logic within the memory allocation mapping function. When CONFIG_DEBUG_VM is enabled, the kernel's debugging infrastructure detects this inconsistency through the VM_WARN_ON_ONCE_PAGE macro, which validates that page reference counts should not be zero during memory mapping operations.
The technical flaw manifests as a mismatch between the expected and actual page reference count behavior in the kernel's memory management subsystem. The p2pmem_alloc_mmap() function contains an assertion that incorrectly validates page reference counts by checking if the count is zero when it should be checking if the count is non-zero. This logical error occurs because the function assumes pages should maintain a reference count greater than zero during mapping operations, but the underlying p2pdma page initialization process correctly sets the reference count to zero. The warning message provides detailed information about the problematic page structure including its reference count, mapping details, zone information, and raw memory contents, indicating that the system has detected an inconsistent page state that could lead to memory corruption or access violations.
The operational impact of this vulnerability extends beyond simple warning messages to potentially destabilize systems running with debug configurations enabled. When the kernel's memory debugging features are active, these warnings can flood system logs and indicate deeper memory management inconsistencies that may affect system reliability. The vulnerability particularly impacts systems utilizing peer-to-peer DMA operations where PCI devices need direct memory access capabilities, potentially affecting data center servers, high-performance computing environments, and embedded systems that rely on efficient memory management for device communication. The issue represents a CWE-254 vulnerability category related to security weaknesses in the kernel's memory management subsystem, specifically concerning improper handling of reference counting mechanisms.
Mitigation strategies should focus on updating the kernel to versions containing the fix that correctly implements the page reference count validation logic. The solution involves modifying the assertion condition from checking for zero reference counts to properly validating that the reference count is non-zero, effectively aligning the kernel's memory management assertions with the actual page initialization behavior. System administrators should ensure their kernel versions include the specific commit b7e282378773 that addresses this inconsistency. Organizations utilizing systems with CONFIG_DEBUG_VM enabled should monitor for these warnings and apply patches promptly, as they may indicate more serious underlying memory management issues that could compromise system security and stability. The fix aligns with ATT&CK technique T1068 by addressing privilege escalation paths through kernel memory management flaws, while also following security best practices outlined in the Linux kernel security documentation for maintaining proper reference counting in kernel memory subsystems.