4.19-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
commit f0e5311aa8022107d63c54e2f03684ec097d1394 upstream.
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 Acked-by: Luis Chamberlain mcgrof@kernel.org Link: https://lore.kernel.org/r/20240828-firmware-traversal-v3-1-c76529c63b5f@goog... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/base/firmware_loader/main.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)
--- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -565,6 +565,26 @@ static void fw_abort_batch_reqs(struct f mutex_unlock(&fw_lock); }
+/* + * Reject firmware file names with ".." path components. + * 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". + * + * Search for ".." surrounded by either '/' or start/end of string. + * + * This intentionally only looks at the firmware name, not at the firmware base + * directory or at symlink contents. + */ +static bool name_contains_dotdot(const char *name) +{ + size_t name_len = strlen(name); + + return strcmp(name, "..") == 0 || strncmp(name, "../", 3) == 0 || + strstr(name, "/../") != NULL || + (name_len >= 3 && strcmp(name+name_len-3, "/..") == 0); +} + /* called from request_firmware() and request_firmware_work_func() */ static int _request_firmware(const struct firmware **firmware_p, const char *name, @@ -582,6 +602,14 @@ _request_firmware(const struct firmware goto out; }
+ if (name_contains_dotdot(name)) { + dev_warn(device, + "Firmware load for '%s' refused, path contains '..' component\n", + name); + ret = -EINVAL; + goto out; + } + ret = _request_firmware_prepare(&fw, name, device, buf, size, opt_flags); if (ret <= 0) /* error or already assigned */ @@ -622,6 +650,8 @@ _request_firmware(const struct firmware * @name will be used as $FIRMWARE in the uevent environment and * should be distinctive enough not to be confused with any other * firmware image for this or any other device. + * It must not contain any ".." path components - "foo/bar..bin" is + * allowed, but "foo/../bar.bin" is not. * * Caller must hold the reference count of @device. *