Vulnerability CVE-2021-47333
Published: 2024-05-21

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
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