On Wed, Aug 28, 2024 at 01:45:48AM +0200, Jann Horn wrote:
> 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:
>
> - lpfc_sli4_request_firmware_update() seems to construct the firmware
> filename from "ModelName", a string that was previously parsed out of
> some descriptor ("Vital Product Data") in lpfc_fill_vpd()
> - nfp_net_fw_find() seems to construct a firmware filename from a model
> name coming from nfp_hwinfo_lookup(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.)
> - module_flash_fw_schedule() is reachable from the
> ETHTOOL_MSG_MODULE_FW_FLASH_ACT netlink command, which is marked as
> GENL_UNS_ADMIN_PERM (meaning CAP_NET_ADMIN 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 CAP_NET_ADMIN 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.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Reviewed-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> Fixes: abb139e75c2c ("firmware: teach the kernel to load firmware files directly from the filesystem")
> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
> ---
Can you also extend tools/testing/selftests/firmware/ with a respective
test for this to ensure it works? With that:
Acked-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Luis
