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b=H4sIAGq+MmUC/53NSwqDMBSF4a1Ixr3FKG1iR91HkRLy0EvVhJsQF HHvTV1Ch/8ZnG9n0RLayB7VzshmjOiXEvxSMT2qZbCApjRr6qblNe8gJlp02MAQZksRwqSS8zT DKu+QRlw+QZm30gFBg1CibU0thXWClctA1uF6cq++9IgxedpOPfPf+ieUOXBQzkjFpbg51z0H7 4fJXrWfWX8cxxdUqE0x6QAAAA== X-Developer-Key: i=justinstitt@google.com; a=ed25519; pk=tC3hNkJQTpNX/gLKxTNQKDmiQl6QjBNCGKJINqAdJsE= X-Developer-Signature: v=1; a=ed25519-sha256; t=1697824366; l=4167; i=justinstitt@google.com; s=20230717; h=from:subject:message-id; bh=IEWFXcfharNOSw9h5QXyYQ0F0PyhdIDYy+kU9BdlLGo=; b=KG9Wfj5pNyAZ1XJPZIdYVUFbz4Ukma8/wGl788PWQAVeEeyVVe1CMIhhOGKuzVpzXzxcMdN04 I8vcKQ+wklFC79kFNxfcUlHEOhUmCgLmeF7saFIpN0VYQoM2Ai9OBBr X-Mailer: b4 0.12.3 Message-ID: <20231020-strncpy-drivers-platform-x86-thinkpad_acpi-c-v1-1-312f2e33034f@google.com> Subject: [PATCH] platform/x86: thinkpad_acpi: replace deprecated strncpy with memcpy From: Justin Stitt To: Kees Cook , Henrique de Moraes Holschuh , Hans de Goede , " =?utf-8?q?Ilpo_J=C3=A4rvinen?= " , Mark Gross Cc: ibm-acpi-devel@lists.sourceforge.net, platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org, Justin Stitt X-Spam-Status: No, score=-8.4 required=5.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lipwig.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (lipwig.vger.email [0.0.0.0]); Fri, 20 Oct 2023 10:53:05 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1780297905134588197 X-GMAIL-MSGID: 1780297905134588197 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 Signed-off-by: Justin Stitt Reviewed-by: Kees Cook Reviewed-by: Mark Pearson --- Note: build-tested only. Found with: $ rg "strncpy\(" --- drivers/platform/x86/thinkpad_acpi.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- base-commit: dab3e01664eaddae965699f1fec776609db0ea9d change-id: 20231019-strncpy-drivers-platform-x86-thinkpad_acpi-c-7a733d087ef7 Best regards, -- Justin Stitt 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;