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

PCI/proc: Use file ns capable() when checking config space read access

proc bus pci read() decides how much of the config space is readable based on capable(CAP SYS ADMIN), which checks the credentials of the task calling read(), not the credentials of the process that opened the file.

The sysfs equivalent, pci read config(), has checked the credentials of the opening process since commit de139a339395 ("pci: check caps from sysfs file open to read device dependent config space"), so a privileged process can open the config space file and pass the file descriptor to an unprivileged process (for example, a process running a KVM guest with an assigned device), which can then read the entire config space. The check was subsequently routed through the LSM framework in commit 47970b1b2aa6 ("pci: use security capable() when checking capablities during config space read") and converted to the dedicated helper in commit ab0fa82b2df9 ("pci-sysfs: use proper file capability helper function").

Thus, the two interfaces check the same capability against different credentials. Checking the credentials of the task calling read() makes the outcome depend on who reads rather than who opened, so the restriction is bypassed whenever a more privileged process reads through the descriptor. Checking the credentials recorded in file->f cred settles the decision at open() time and ties it to the file, where it cannot change with the caller.

Use file ns capable() to check CAP SYS ADMIN against the credentials in effect when the file was opened, bringing the procfs interface in line with the sysfs behaviour.

As a result, a file descriptor opened by a privileged process and passed to an unprivileged one now allows the entire config space to be read through procfs, matching sysfs.