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942a4a61b6
strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous
interfaces.
We expect ec_fw_string to be NUL-terminated based on its use with format
strings in thinkpad_acpi.c:
11241 | pr_notice("ThinkPad firmware release %s doesn't match the known patterns\n",
11242 | ec_fw_string);
Moreover, NUL-padding is not required since ec_fw_string is explicitly
zero-initialized:
11185 | char ec_fw_string[18] = {0};
When carefully copying bytes from one buffer to another in
pre-determined blocks (like what's happening here with dmi_data):
| static void find_new_ec_fwstr(const struct dmi_header *dm, void *private)
| {
| char *ec_fw_string = (char *) private;
| const char *dmi_data = (const char *)dm;
| /*
| * ThinkPad Embedded Controller Program Table on newer models
| *
| * Offset | Name | Width | Description
| * ----------------------------------------------------
| * 0x00 | Type | BYTE | 0x8C
| * 0x01 | Length | BYTE |
| * 0x02 | Handle | WORD | Varies
| * 0x04 | Signature | BYTEx6 | ASCII for "LENOVO"
| * 0x0A | OEM struct offset | BYTE | 0x0B
| * 0x0B | OEM struct number | BYTE | 0x07, for this structure
| * 0x0C | OEM struct revision | BYTE | 0x01, for this format
| * 0x0D | ECP version ID | STR ID |
| * 0x0E | ECP release date | STR ID |
| */
|
| /* Return if data structure not match */
| if (dm->type != 140 || dm->length < 0x0F ||
| memcmp(dmi_data + 4, "LENOVO", 6) != 0 ||
| dmi_data[0x0A] != 0x0B || dmi_data[0x0B] != 0x07 ||
| dmi_data[0x0C] != 0x01)
| return;
|
| /* fwstr is the first 8byte string */
| strncpy(ec_fw_string, dmi_data + 0x0F, 8);
... we shouldn't be using a C string api. Let's instead use memcpy() as
this more properly relays the intended behavior.
Do note that ec_fw_string will still end up being NUL-terminated since
we are memcpy'ing only 8 bytes into a buffer full of 18 zeroes. There's
still some trailing NUL-bytes there. To ensure this behavior, let's add
a BUILD_BUG_ON checking the length leaves space for at least one
trailing NUL-byte.
Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231020-strncpy-drivers-platform-x86-thinkpad_acpi-c-v1-1-312f2e33034f@google.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.