bnxt: Do not read past the end of test names

Test names were being concatenated based on a offset beyond the end of
the first name, which tripped the buffer overflow detection logic:

 detected buffer overflow in strnlen
 [...]
 Call Trace:
 bnxt_ethtool_init.cold+0x18/0x18

Refactor struct hwrm_selftest_qlist_output to use an actual array,
and adjust the concatenation to use snprintf() rather than a series of
strncat() calls.

Reported-by: Niklas Cassel <[email protected]>
Link: https://lore.kernel.org/lkml/Y8F%2F1w1AZTvLglFX@x1-carbon/
Tested-by: Niklas Cassel <[email protected]>
Fixes: eb51365 ("bnxt_en: Add basic ethtool -t selftest support.")
Cc: Michael Chan <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Michael Chan <[email protected]>
Reviewed-by: Niklas Cassel <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: kees

drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c

@@ -3969,7 +3969,7 @@ void bnxt_ethtool_init(struct bnxt *bp)
 		test_info->timeout = HWRM_CMD_TIMEOUT;
 	for (i = 0; i < bp->num_tests; i++) {
 		char *str = test_info->string[i];
-		char *fw_str = resp->test0_name + i * 32;
+		char *fw_str = resp->test_name[i];
 
 		if (i == BNXT_MACLPBK_TEST_IDX) {
 			strcpy(str, "Mac loopback test (offline)");
@@ -3980,14 +3980,9 @@ void bnxt_ethtool_init(struct bnxt *bp)
 		} else if (i == BNXT_IRQ_TEST_IDX) {
 			strcpy(str, "Interrupt_test (offline)");
 		} else {
-			strscpy(str, fw_str, ETH_GSTRING_LEN);
-			strncat(str, " test", ETH_GSTRING_LEN - strlen(str));
-			if (test_info->offline_mask & (1 << i))
-				strncat(str, " (offline)",
-					ETH_GSTRING_LEN - strlen(str));
-			else
-				strncat(str, " (online)",
-					ETH_GSTRING_LEN - strlen(str));
+			snprintf(str, ETH_GSTRING_LEN, "%s test (%s)",
+				 fw_str, test_info->offline_mask & (1 << i) ?
+					"offline" : "online");
 		}
 	}
 

drivers/net/ethernet/broadcom/bnxt/bnxt_hsi.h

@@ -10249,14 +10249,7 @@ struct hwrm_selftest_qlist_output {
 	u8	unused_0;
 	__le16	test_timeout;
 	u8	unused_1[2];
-	char	test0_name[32];
-	char	test1_name[32];
-	char	test2_name[32];
-	char	test3_name[32];
-	char	test4_name[32];
-	char	test5_name[32];
-	char	test6_name[32];
-	char	test7_name[32];
+	char	test_name[8][32];
 	u8	eyescope_target_BER_support;
 	#define SELFTEST_QLIST_RESP_EYESCOPE_TARGET_BER_SUPPORT_BER_1E8_SUPPORTED  0x0UL
 	#define SELFTEST_QLIST_RESP_EYESCOPE_TARGET_BER_SUPPORT_BER_1E9_SUPPORTED  0x1UL