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firmware_loader: Block path traversal

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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: abb139e75c ("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@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jann Horn 2024-08-28 01:45:48 +02:00 committed by Greg Kroah-Hartman
parent 888f67e621
commit f0e5311aa8
1 changed files with 30 additions and 0 deletions
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30
drivers/base/firmware_loader/main.c
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@ -849,6 +849,26 @@ static void fw_log_firmware_info(const struct firmware *fw, const char *name,
{}
#endif
/*
* 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,
@ -869,6 +889,14 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
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,
offset, opt_flags);
if (ret <= 0) /* error or already assigned */
@ -946,6 +974,8 @@ out:
* @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.
*