CVE-2025-40032 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
PCI: endpoint: pci-epf-test: Add NULL check for DMA channels before release
The fields dma_chan_tx and dma_chan_rx of the struct pci_epf_test can be NULL even after EPF initialization. Then it is prudent to check that they have non-NULL values before releasing the channels. Add the checks in pci_epf_test_clean_dma_chan().
Without the checks, NULL pointer dereferences happen and they can lead to a kernel panic in some cases:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050 Call trace: dma_release_channel+0x2c/0x120 (P) pci_epf_test_epc_deinit+0x94/0xc0 [pci_epf_test]
pci_epc_deinit_notify+0x74/0xc0 tegra_pcie_ep_pex_rst_irq+0x250/0x5d8 irq_thread_fn+0x34/0xb8 irq_thread+0x18c/0x2e8 kthread+0x14c/0x210 ret_from_fork+0x10/0x20
[mani: trimmed the stack trace]
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Analysis
by VulDB Data Team • 05/19/2026
This vulnerability exists within the Linux kernel's PCI endpoint framework, specifically in the pci-epf-test driver component that handles endpoint function testing. The issue manifests as a null pointer dereference condition that occurs during the cleanup phase of DMA channel management. The vulnerability stems from the fact that the dma_chan_tx and dma_chan_rx fields within the pci_epf_test structure can legitimately remain NULL even after successful endpoint function initialization has completed. This scenario typically arises when DMA channels are not properly allocated or configured during the initialization sequence, leaving these pointers in an uninitialized state.
The technical flaw represents a classic defensive programming error where the code assumes that DMA channels will always be properly allocated and initialized, failing to account for the possibility of partial initialization failures or conditional allocation paths. When the pci_epf_test_clean_dma_chan() function attempts to release these channels without proper validation, it directly dereferences potentially NULL pointers, leading to immediate system instability. The kernel panic occurs because the code follows a null pointer to virtual address 0x0000000000000050, which triggers the kernel's page fault handler and results in an unrecoverable system crash.
The operational impact of this vulnerability is significant as it can cause complete system crashes during endpoint function deinitialization, particularly in PCIe endpoint controller implementations such as those found in tegra systems. This vulnerability affects systems that utilize the pci-epf-test driver for endpoint function testing, potentially disrupting device initialization sequences and causing system-wide instability. The vulnerability is particularly concerning because it occurs during cleanup operations, meaning it can affect systems that are already operational, potentially causing data loss or requiring complete system reboots.
The fix implemented addresses this issue by adding explicit null pointer checks within the pci_epf_test_clean_dma_chan() function before attempting to release DMA channels. This follows the fundamental principle of defensive programming and aligns with CWE-476 which identifies null pointer dereference as a critical weakness in software design. The mitigation approach directly addresses the root cause by ensuring that DMA channel release operations only occur when the channels are actually valid, preventing the kernel from attempting to dereference invalid memory addresses. This remediation also aligns with ATT&CK technique T1490 which involves system network configuration modification, as proper null validation prevents unauthorized access to kernel memory through controlled crash conditions.
This vulnerability demonstrates the importance of robust error handling in kernel space code where resource management failures can lead to complete system compromise. The fix ensures that endpoint function testing components properly validate their internal state before attempting resource cleanup operations, preventing the kernel from entering an undefined state during device deinitialization. The solution maintains backward compatibility while strengthening the driver's resilience against partial initialization failures that may occur in complex PCIe endpoint controller configurations.