CVE-2024-47742: firmware_loader: Block path traversal

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

firmwareloader: Block path traversal

Most firmware names are hardcoded strings, or are constructed from fairly constrained format strings where the dynamic parts are just some hex numbers or such.

However, there are a couple codepaths in the kernel where firmware file names contain string components that are passed through from a device or semi-privileged userspace; the ones I could find (not counting interfaces that require root privileges) are:

- lpfcsli4requestfirmwareupdate() seems to construct the firmware filename from "ModelName", a string that was previously parsed out of some descriptor ("Vital Product Data") in lpfcfillvpd() - nfpnetfwfind() seems to construct a firmware filename from a model name coming from nfphwinfolookup(pf->hwinfo, "nffw.partno"), which I think parses some descriptor that was read from the device. (But this case likely isn't exploitable because the format string looks like "netronome/nic%s", and there shouldn't be any folders starting with "netronome/nic". The previous case was different because there, the "%s" is at the start of the format string.) - moduleflashfwschedule() is reachable from the ETHTOOLMSGMODULEFWFLASHACT netlink command, which is marked as GENLUNSADMINPERM (meaning CAPNETADMIN inside a user namespace is enough to pass the privilege check), and takes a userspace-provided firmware name. (But I think to reach this case, you need to have CAPNETADMIN over a network namespace that a special kind of ethernet device is mapped into, so I think this is not a viable attack path in practice.)

Fix it by rejecting any firmware names containing ".." path components.

For what it's worth, I went looking and haven't found any USB device drivers that use the firmware loader dangerously.