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@xxxxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
Note: build-tested only.
Found with: $ rg "strncpy\("
---
drivers/platform/x86/thinkpad_acpi.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
index 41584427dc32..bd9e06f5b860 100644
--- a/drivers/platform/x86/thinkpad_acpi.c
+++ b/drivers/platform/x86/thinkpad_acpi.c
@@ -11144,6 +11144,8 @@ static char __init tpacpi_parse_fw_id(const char * const s,
return '\0';
}
+#define EC_FW_STRING_LEN 18
+
static void find_new_ec_fwstr(const struct dmi_header *dm, void *private)
{
char *ec_fw_string = (char *) private;
@@ -11172,7 +11174,8 @@ static void find_new_ec_fwstr(const struct dmi_header *dm, void *private)
return;
/* fwstr is the first 8byte string */
- strncpy(ec_fw_string, dmi_data + 0x0F, 8);
+ BUILD_BUG_ON(EC_FW_STRING_LEN <= 8);
+ memcpy(ec_fw_string, dmi_data + 0x0F, 8);
}
/* returns 0 - probe ok, or < 0 - probe error.
@@ -11182,7 +11185,7 @@ static int __must_check __init get_thinkpad_model_data(
struct thinkpad_id_data *tp)
{
const struct dmi_device *dev = NULL;
- char ec_fw_string[18] = {0};
+ char ec_fw_string[EC_FW_STRING_LEN] = {0};
char const *s;
char t;
---
base-commit: dab3e01664eaddae965699f1fec776609db0ea9d
change-id: 20231019-strncpy-drivers-platform-x86-thinkpad_acpi-c-7a733d087ef7
Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>
