In the Linux kernel, the following vulnerability has been resolved:vfio/pci: Properly hide first-in-list PCIe extended capabilityThere are cases where a PCIe extended capability should be hidden fromthe user. For example, an unknown capability (i.e., capability with IDgreater than PCI_EXT_CAP_ID_MAX) or a capability that is intentionallychosen to be hidden from the user.Hiding a capability is done by virtualizing and modifying the 'NextCapability Offset' field of the previous capability so it points to thecapability after the one that should be hidden.The special case where the first capability in the list should be hiddenis handled differently because there is no previous capability that canbe modified. In this case, the capability ID and version are zeroedwhile leaving the next pointer intact. This hides the capability andleaves an anchor for the rest of the capability list.However, today, hiding the first capability in the list is not doneproperly if the capability is unknown, as structvfio_pci_core_device->pci_config_map is set to the capability ID duringinitialization but the capability ID is not properly checked later whenused in vfio_config_do_rw(). This leads to the following warning [1] andto an out-of-bounds access to ecap_perms array.Fix it by checking cap_id in vfio_config_do_rw(), and if it is greaterthan PCI_EXT_CAP_ID_MAX, use an alternative struct perm_bits for directread only access instead of the ecap_perms array.Note that this is safe since the above is the only case where cap_id canexceed PCI_EXT_CAP_ID_MAX (except for the special capabilities, whichare already checked before).[1]WARNING: CPU: 118 PID: 5329 at drivers/vfio/pci/vfio_pci_config.c:1900 vfio_pci_config_rw+0x395/0x430 [vfio_pci_core]CPU: 118 UID: 0 PID: 5329 Comm: simx-qemu-syste Not tainted 6.12.0+ #1(snip)Call Trace: <TASK> ? show_regs+0x69/0x80 ? __warn+0x8d/0x140 ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] ? report_bug+0x18f/0x1a0 ? handle_bug+0x63/0xa0 ? exc_invalid_op+0x19/0x70 ? asm_exc_invalid_op+0x1b/0x20 ? vfio_pci_config_rw+0x395/0x430 [vfio_pci_core] ? vfio_pci_config_rw+0x244/0x430 [vfio_pci_core] vfio_pci_rw+0x101/0x1b0 [vfio_pci_core] vfio_pci_core_read+0x1d/0x30 [vfio_pci_core] vfio_device_fops_read+0x27/0x40 [vfio] vfs_read+0xbd/0x340 ? vfio_device_fops_unl_ioctl+0xbb/0x740 [vfio] ? __rseq_handle_notify_resume+0xa4/0x4b0 __x64_sys_pread64+0x96/0xc0 x64_sys_call+0x1c3d/0x20d0 do_syscall_64+0x4d/0x120 entry_SYSCALL_64_after_hwframe+0x76/0x7e
