linux-kernel - [PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

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Message-Id: <20211118142124.526901-1-arnd@kernel.org>
Date:   Thu, 18 Nov 2021 15:21:02 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Luca Coelho <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>
Cc:     Arnd Bergmann <arnd@...db.de>, kernel test robot <lkp@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Yaara Baruch <yaara.baruch@...el.com>,
        Matti Gottlieb <matti.gottlieb@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] [v3] iwlwifi: pcie: fix constant-conversion warning

From: Arnd Bergmann <arnd@...db.de>

gcc-11 points out a potential issue with integer overflow when
the iwl_dev_info_table[] array is empty:

drivers/net/wireless/intel/iwlwifi/pcie/drv.c:1344:42: error: implicit conversion from 'unsigned long' to 'int' changes value from 18446744073709551615 to -1 [-Werror,-Wconstant-conversion]
        for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
               ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

This is still harmless, as the loop correctly terminates, but adding
an extra range check makes that obvious to both readers and to the
compiler.

Fixes: 3f7320428fa4 ("iwlwifi: pcie: simplify iwl_pci_find_dev_info()")
Reported-by: kernel test robot <lkp@...el.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Changes in v3:
- make it actually work with gcc-11
- fix commit message s/clang/gcc-11/

Changes in v2:
- replace int cast with a range check
---
 drivers/net/wireless/intel/iwlwifi/pcie/drv.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
index c574f041f096..395e328c6a07 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/drv.c
@@ -1339,9 +1339,13 @@ iwl_pci_find_dev_info(u16 device, u16 subsystem_device,
 		      u16 mac_type, u8 mac_step,
 		      u16 rf_type, u8 cdb, u8 rf_id, u8 no_160, u8 cores)
 {
+	int num_devices = ARRAY_SIZE(iwl_dev_info_table);
 	int i;
 
-	for (i = ARRAY_SIZE(iwl_dev_info_table) - 1; i >= 0; i--) {
+	if (!num_devices)
+		return NULL;
+
+	for (i = num_devices - 1; i >= 0; i--) {
 		const struct iwl_dev_info *dev_info = &iwl_dev_info_table[i];
 
 		if (dev_info->device != (u16)IWL_CFG_ANY &&
-- 
2.29.2