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@vger.kernel.org Reviewed-by: Danilo Krummrich dakr@kernel.org Fixes: abb139e75c2c ("firmware: teach the kernel to load firmware files directly from the filesystem") Signed-off-by: Jann Horn jannh@google.com
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@kernel.org
Luis