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.)
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 Fixes: abb139e75c2c ("firmware: teach the kernel to load firmware files directly from the filesystem") Signed-off-by: Jann Horn jannh@google.com --- I wasn't sure whether to mark this one for stable or not - but I think since there seems to be at least one PCI device model which could trigger firmware loading with directory traversal, we should probably backport the fix? --- drivers/base/firmware_loader/main.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index a03ee4b11134..a32be64f3bf5 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -864,7 +864,15 @@ _request_firmware(const struct firmware **firmware_p, const char *name, if (!firmware_p) return -EINVAL;
- if (!name || name[0] == '\0') { + /* + * Reject firmware file names with "/../" sequences in them. + * There are drivers that construct firmware file names from + * device-supplied strings, and we don't want some device to be able + * to tell us "I would like to be sent my firmware from + * ../../../etc/shadow, please". + */ + if (!name || name[0] == '\0' || + strstr(name, "/../") != NULL || strncmp(name, "../", 3) == 0) { ret = -EINVAL; goto out; }
--- base-commit: b0da640826ba3b6506b4996a6b23a429235e6923 change-id: 20240820-firmware-traversal-6df8501b0fe4