misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: misc: alcor_pci: fix null-ptr-deref when there is no PCI bridge There is an issue with the ASPM(optional) capability checking function. A device might be attached to root complex directly, in this case, bus->self(bridge) will be NULL, thus priv->parent_pdev is NULL. Since alcor_pci_init_check_aspm(priv->parent_pdev) checks the PCI link's ASPM capability and populate parent_cap_off, which will be used later by alcor_pci_aspm_ctrl() to dynamically turn on/off device, what we can do here is to avoid checking the capability if we are on the root complex. This will make pdev_cap_off 0 and alcor_pci_aspm_ctrl() will simply return when bring called, effectively disable ASPM for the device. [ 1.246492] BUG: kernel NULL pointer dereference, address: 00000000000000c0 [ 1.248731] RIP: 0010:pci_read_config_byte+0x5/0x40 [ 1.253998] Call Trace: [ 1.254131] ? alcor_pci_find_cap_offset.isra.0+0x3a/0x100 [alcor_pci] [ 1.254476] alcor_pci_probe+0x169/0x2d5 [alcor_pci]

References

• https://git.kernel.org/stable/c/d2639ffdcad463b358b6bef8645ff81715daffcb
• https://git.kernel.org/stable/c/58f69684ba03e5b0e0a3ae844a845280c0f06309
• https://git.kernel.org/stable/c/717cf5ae52322ddbdf3ac2c584b34c5970b0d174
• https://git.kernel.org/stable/c/09d154990ca82d14aed2b72796f6c8845e2e605d
• https://git.kernel.org/stable/c/3ce3e45cc333da707d4d6eb433574b990bcc26f5