PCI: endpoint: pci-epf-test: Add NULL check for DMA channels before release

Vulnerability Description

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]

References

• https://git.kernel.org/stable/c/6411f840a9b5c47c00ca8e004733de232553870d
• https://git.kernel.org/stable/c/0c5ce6b6ccc22d486cc7239ed908cb0ae5363a7b
• https://git.kernel.org/stable/c/fb54ffd60064c4e5139a3eb216e877b1acae1c8b
• https://git.kernel.org/stable/c/57f7fb0d1ac28540c0f6405c829bb9c3b89d8dba
• https://git.kernel.org/stable/c/85afa9ea122dd9d4a2ead104a951d318975dcd25