[PATCH] [v2] hinic: avoid gcc -Wrestrict warning

Subsystems: huawei ethernet driver, networking drivers, the rest

STALE1957d

4 messages, 3 authors, 2021-03-25 · open the first message on its own page

[PATCH] [v2] hinic: avoid gcc -Wrestrict warning

From: Arnd Bergmann <arnd@kernel.org>
Date: 2021-03-24 13:08:22

From: Arnd Bergmann <arnd@arndb.de>

With extra warnings enabled, gcc complains that snprintf should not
take the same buffer as source and destination:

drivers/net/ethernet/huawei/hinic/hinic_ethtool.c: In function 'hinic_set_settings_to_hw':
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:480:9: error: 'snprintf' argument 4 overlaps destination object 'set_link_str' [-Werror=restrict]
  480 |   err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  481 |           "%sspeed %d ", set_link_str, speed);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:464:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
  464 |  char set_link_str[SET_LINK_STR_MAX_LEN] = {0};

Rewrite this to avoid the nested sprintf and instead use separate
buffers, which is simpler.

Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: rework according to feedback from Rasmus. This one could
    easily avoid most of the pitfalls
---
 .../net/ethernet/huawei/hinic/hinic_ethtool.c | 25 ++++++++-----------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c b/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c
index c340d9acba80..d7e20dab6e48 100644
--- a/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c
+++ b/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c

@@ -34,7 +34,7 @@
 #include "hinic_rx.h"
 #include "hinic_dev.h"
 
-#define SET_LINK_STR_MAX_LEN	128
+#define SET_LINK_STR_MAX_LEN	16
 
 #define GET_SUPPORTED_MODE	0
 #define GET_ADVERTISED_MODE	1

@@ -462,24 +462,19 @@ static int hinic_set_settings_to_hw(struct hinic_dev *nic_dev,
 {
 	struct hinic_link_ksettings_info settings = {0};
 	char set_link_str[SET_LINK_STR_MAX_LEN] = {0};
+	const char *autoneg_str;
 	struct net_device *netdev = nic_dev->netdev;
 	enum nic_speed_level speed_level = 0;
 	int err;
 
-	err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN, "%s",
-		       (set_settings & HILINK_LINK_SET_AUTONEG) ?
-		       (autoneg ? "autong enable " : "autong disable ") : "");
-	if (err < 0 || err >= SET_LINK_STR_MAX_LEN) {
-		netif_err(nic_dev, drv, netdev, "Failed to snprintf link state, function return(%d) and dest_len(%d)\n",
-			  err, SET_LINK_STR_MAX_LEN);
-		return -EFAULT;
-	}
+	autoneg_str = (set_settings & HILINK_LINK_SET_AUTONEG) ?
+		      (autoneg ? "autong enable " : "autong disable ") : "";
 
 	if (set_settings & HILINK_LINK_SET_SPEED) {
 		speed_level = hinic_ethtool_to_hw_speed_level(speed);
 		err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
-			       "%sspeed %d ", set_link_str, speed);
-		if (err <= 0 || err >= SET_LINK_STR_MAX_LEN) {
+			       "speed %d ", speed);
+		if (err >= SET_LINK_STR_MAX_LEN) {
 			netif_err(nic_dev, drv, netdev, "Failed to snprintf link speed, function return(%d) and dest_len(%d)\n",
 				  err, SET_LINK_STR_MAX_LEN);
 			return -EFAULT;

@@ -494,11 +489,11 @@ static int hinic_set_settings_to_hw(struct hinic_dev *nic_dev,
 	err = hinic_set_link_settings(nic_dev->hwdev, &settings);
 	if (err != HINIC_MGMT_CMD_UNSUPPORTED) {
 		if (err)
-			netif_err(nic_dev, drv, netdev, "Set %s failed\n",
-				  set_link_str);
+			netif_err(nic_dev, drv, netdev, "Set %s%sfailed\n",
+				  autoneg_str, set_link_str);
 		else
-			netif_info(nic_dev, drv, netdev, "Set %s successfully\n",
-				   set_link_str);
+			netif_info(nic_dev, drv, netdev, "Set %s%ssuccessfully\n",
+				   autoneg_str, set_link_str);
 
 		return err;
 	}

-- 
2.29.2

Re: [PATCH] [v2] hinic: avoid gcc -Wrestrict warning

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Date: 2021-03-24 13:30:30

On 24/03/2021 14.07, Arnd Bergmann wrote:

From: Arnd Bergmann <arnd@arndb.de>

With extra warnings enabled, gcc complains that snprintf should not
take the same buffer as source and destination:

drivers/net/ethernet/huawei/hinic/hinic_ethtool.c: In function 'hinic_set_settings_to_hw':
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:480:9: error: 'snprintf' argument 4 overlaps destination object 'set_link_str' [-Werror=restrict]
  480 |   err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  481 |           "%sspeed %d ", set_link_str, speed);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:464:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
  464 |  char set_link_str[SET_LINK_STR_MAX_LEN] = {0};

Rewrite this to avoid the nested sprintf and instead use separate
buffers, which is simpler.

This looks much better. Thanks.

quoted hunk

Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
v2: rework according to feedback from Rasmus. This one could
    easily avoid most of the pitfalls
---
 .../net/ethernet/huawei/hinic/hinic_ethtool.c | 25 ++++++++-----------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c b/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c
index c340d9acba80..d7e20dab6e48 100644
--- a/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c
+++ b/drivers/net/ethernet/huawei/hinic/hinic_ethtool.c

@@ -34,7 +34,7 @@
 #include "hinic_rx.h"
 #include "hinic_dev.h"
 
-#define SET_LINK_STR_MAX_LEN	128
+#define SET_LINK_STR_MAX_LEN	16
 
 #define GET_SUPPORTED_MODE	0
 #define GET_ADVERTISED_MODE	1

@@ -462,24 +462,19 @@ static int hinic_set_settings_to_hw(struct hinic_dev *nic_dev,
 {
 	struct hinic_link_ksettings_info settings = {0};
 	char set_link_str[SET_LINK_STR_MAX_LEN] = {0};
+	const char *autoneg_str;
 	struct net_device *netdev = nic_dev->netdev;
 	enum nic_speed_level speed_level = 0;
 	int err;
 
-	err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN, "%s",
-		       (set_settings & HILINK_LINK_SET_AUTONEG) ?
-		       (autoneg ? "autong enable " : "autong disable ") : "");
-	if (err < 0 || err >= SET_LINK_STR_MAX_LEN) {
-		netif_err(nic_dev, drv, netdev, "Failed to snprintf link state, function return(%d) and dest_len(%d)\n",
-			  err, SET_LINK_STR_MAX_LEN);
-		return -EFAULT;
-	}
+	autoneg_str = (set_settings & HILINK_LINK_SET_AUTONEG) ?
+		      (autoneg ? "autong enable " : "autong disable ") : "";
 
 	if (set_settings & HILINK_LINK_SET_SPEED) {
 		speed_level = hinic_ethtool_to_hw_speed_level(speed);
 		err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
-			       "%sspeed %d ", set_link_str, speed);
-		if (err <= 0 || err >= SET_LINK_STR_MAX_LEN) {
+			       "speed %d ", speed);
+		if (err >= SET_LINK_STR_MAX_LEN) {
 			netif_err(nic_dev, drv, netdev, "Failed to snprintf link speed, function return(%d) and dest_len(%d)\n",
 				  err, SET_LINK_STR_MAX_LEN);
 			return -EFAULT;

It's not your invention of course, but this both seems needlessly harsh
and EFAULT is a weird error to return. It's just a printk() message that
might be truncated, and now that the format string only has a %d
specifier, it can actually be verified statically that overflow will
never happen (though I don't know or think gcc can do that, perhaps
there's some locale nonsense in the standard that allows using
utf16-encoded sanskrit runes). So probably that test should just be
dropped, but that's a separate thing.

Reviewed-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>

Re: [PATCH] [v2] hinic: avoid gcc -Wrestrict warning

From: Arnd Bergmann <arnd@kernel.org>
Date: 2021-03-24 14:26:59

On Wed, Mar 24, 2021 at 2:29 PM Rasmus Villemoes
[off-list ref] wrote:

On 24/03/2021 14.07, Arnd Bergmann wrote:

quoted

      if (set_settings & HILINK_LINK_SET_SPEED) {
              speed_level = hinic_ethtool_to_hw_speed_level(speed);
              err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
-                            "%sspeed %d ", set_link_str, speed);
-             if (err <= 0 || err >= SET_LINK_STR_MAX_LEN) {
+                            "speed %d ", speed);
+             if (err >= SET_LINK_STR_MAX_LEN) {
                      netif_err(nic_dev, drv, netdev, "Failed to snprintf link speed, function return(%d) and dest_len(%d)\n",
                                err, SET_LINK_STR_MAX_LEN);
                      return -EFAULT;

It's not your invention of course, but this both seems needlessly harsh
and EFAULT is a weird error to return. It's just a printk() message that
might be truncated, and now that the format string only has a %d
specifier, it can actually be verified statically that overflow will
never happen (though I don't know or think gcc can do that, perhaps
there's some locale nonsense in the standard that allows using
utf16-encoded sanskrit runes). So probably that test should just be
dropped, but that's a separate thing.

I thought about fixing it, but this seemed to be a rabbit hole I didn't
want to get into, as there are other harmless issues in the driver
that could be improved.

I'm fairly sure gcc can indeed warn about the overflow with
-Wformat-truncation, but the warning is disabled at the moment
because it has a ton of false positives:

kernel/workqueue.c: In function 'create_worker':
kernel/workqueue.c:1933:55: error: '%d' directive output may be
truncated writing between 1 and 10 bytes into a region of size between
3 and 13 [-Werror=format-truncation=]
 1933 |                 snprintf(id_buf, sizeof(id_buf), "u%d:%d",
pool->id, id);

        Arnd

Re: [PATCH] [v2] hinic: avoid gcc -Wrestrict warning

From: patchwork-bot+netdevbpf@kernel.org
Date: 2021-03-25 01:10:51

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Wed, 24 Mar 2021 14:07:22 +0100 you wrote:

From: Arnd Bergmann <arnd@arndb.de>

With extra warnings enabled, gcc complains that snprintf should not
take the same buffer as source and destination:

drivers/net/ethernet/huawei/hinic/hinic_ethtool.c: In function 'hinic_set_settings_to_hw':
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:480:9: error: 'snprintf' argument 4 overlaps destination object 'set_link_str' [-Werror=restrict]
  480 |   err = snprintf(set_link_str, SET_LINK_STR_MAX_LEN,
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  481 |           "%sspeed %d ", set_link_str, speed);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/huawei/hinic/hinic_ethtool.c:464:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
  464 |  char set_link_str[SET_LINK_STR_MAX_LEN] = {0};

[...]

Here is the summary with links:
  - [v2] hinic: avoid gcc -Wrestrict warning
    https://git.kernel.org/netdev/net-next/c/84c7f6c33f42

You are awesome, thank you!
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