[PATCH 62/82] mwifiex: pcie: Refactor intentional wrap-around test

[Kees Cook]

In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:

	VAR + value < VAR

Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.

Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.

Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Brian Norris <briannorris@xxxxxxxxxxxx>
Cc: Kalle Valo <kvalo@xxxxxxxxxx>
Cc: "Jonas Dreßler" <verdre@xxxxxxx>
Cc: Dmitry Antipov <dmantipov@xxxxxxxxx>
Cc: Tsuchiya Yuto <kitakar@xxxxxxxxx>
Cc: linux-wireless@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/net/wireless/marvell/mwifiex/pcie.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/pcie.c b/drivers/net/wireless/marvell/mwifiex/pcie.c
index 5f997becdbaa..e69347e65f0e 100644
--- a/drivers/net/wireless/marvell/mwifiex/pcie.c
+++ b/drivers/net/wireless/marvell/mwifiex/pcie.c
@@ -2086,7 +2086,7 @@ static int mwifiex_extract_wifi_fw(struct mwifiex_adapter *adapter,
 
 		switch (dnld_cmd) {
 		case MWIFIEX_FW_DNLD_CMD_1:
-			if (offset + data_len < data_len) {
+			if (add_would_overflow(data_len, offset)) {
 				mwifiex_dbg(adapter, ERROR, "bad FW parse\n");
 				ret = -1;
 				goto done;
@@ -2110,7 +2110,7 @@ static int mwifiex_extract_wifi_fw(struct mwifiex_adapter *adapter,
 		case MWIFIEX_FW_DNLD_CMD_5:
 			first_cmd = true;
 			/* Check for integer overflow */
-			if (offset + data_len < data_len) {
+			if (add_would_overflow(data_len, offset)) {
 				mwifiex_dbg(adapter, ERROR, "bad FW parse\n");
 				ret = -1;
 				goto done;
@@ -2120,7 +2120,7 @@ static int mwifiex_extract_wifi_fw(struct mwifiex_adapter *adapter,
 		case MWIFIEX_FW_DNLD_CMD_6:
 			first_cmd = true;
 			/* Check for integer overflow */
-			if (offset + data_len < data_len) {
+			if (add_would_overflow(data_len, offset)) {
 				mwifiex_dbg(adapter, ERROR, "bad FW parse\n");
 				ret = -1;
 				goto done;
-- 
2.34.1