netdev - [PATCH net-next v2] net: remove redundant input checks in SIOCSIFTXQLEN case of dev

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Date:   Tue, 24 Jul 2018 13:53:00 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, Eran Ben Elisha <eranbe@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>,
        Cong Wang <xiyou.wangcong@...il.com>
Subject: [PATCH net-next v2] net: remove redundant input checks in SIOCSIFTXQLEN case of dev_ifsioc

The cited patch added a call to dev_change_tx_queue_len in
SIOCSIFTXQLEN case.
This obsoletes the new len comparison check done before the function call.
Remove it here.

For the desicion of keep/remove the negative value check, we examine the
range check in dev_change_tx_queue_len.
On 64-bit we will fail with -ERANGE.  The 32-bit int ifr_qlen will be sign
extended to 64-bits when it is passed into dev_change_tx_queue_len(). And
then for negative values this test triggers:

	if (new_len != (unsigned int)new_len)
		return -ERANGE;

because:
	if (0xffffffffWHATEVER != 0x00000000WHATEVER)

On 32-bit the signed value will be accepted, changing behavior.

Therefore, the negative value check is kept.

Fixes: 3f76df198288 ("net: use dev_change_tx_queue_len() for SIOCSIFTXQLEN")
Signed-off-by: Tariq Toukan <tariqt@...lanox.com>
Reviewed-by: Eran Ben Elisha <eranbe@...lanox.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>
---
 net/core/dev_ioctl.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

v1 -> v2:
* Retained negative value check, per comments from Cong and Dave.
* Updated commit message accordingly.

diff --git a/net/core/dev_ioctl.c b/net/core/dev_ioctl.c
index 50537ff961a7..90e8aa36881e 100644
--- a/net/core/dev_ioctl.c
+++ b/net/core/dev_ioctl.c
@@ -284,12 +284,7 @@ static int dev_ifsioc(struct net *net, struct ifreq *ifr, unsigned int cmd)
 	case SIOCSIFTXQLEN:
 		if (ifr->ifr_qlen < 0)
 			return -EINVAL;
-		if (dev->tx_queue_len ^ ifr->ifr_qlen) {
-			err = dev_change_tx_queue_len(dev, ifr->ifr_qlen);
-			if (err)
-				return err;
-		}
-		return 0;
+		return dev_change_tx_queue_len(dev, ifr->ifr_qlen);

 	case SIOCSIFNAME:
 		ifr->ifr_newname[IFNAMSIZ-1] = '\0';
-- 
1.8.3.1