PCI: endpoint: Fix NULL pointer dereference for ->get_features()

In the Linux kernel, the following vulnerability has been resolved:

PCI: endpoint: Fix NULL pointer dereference for ->get_features()

get_features ops of pci_epc_ops may return NULL, causing NULL pointer

dereference in pci_epf_test_alloc_space function. Let us add a check for

pci_epc_feature pointer in pci_epf_test_bind before we access it to avoid

any such NULL pointer dereference and return -ENOTSUPP in case

pci_epc_feature is not found.

When the patch is not applied and EPC features is not implemented in the

platform driver, we see the following dump due to kernel NULL pointer

dereference.

Call trace:

pci_epf_test_bind+0xf4/0x388

pci_epf_bind+0x3c/0x80

pci_epc_epf_link+0xa8/0xcc

configfs_symlink+0x1a4/0x48c

vfs_symlink+0x104/0x184

do_symlinkat+0x80/0xd4

__arm64_sys_symlinkat+0x1c/0x24

el0_svc_common.constprop.3+0xb8/0x170

el0_svc_handler+0x70/0x88

el0_svc+0x8/0x640

Code: d2800581 b9403ab9 f9404ebb 8b394f60 (f9400400)

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