netdev - [PATCH 1/1] macvtap: Fix regression for macvtap ioctls

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Date:	Fri, 18 Sep 2015 09:54:44 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	stable@...r.kernel.org, netdev@...r.kernel.org,
	Matthew Rosato <mjrosato@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Christian Borntraeger <borntraeger@...ibm.com>
Subject: [PATCH 1/1] macvtap: Fix regression for macvtap ioctls

To avoid overwriting the upper bits of the flags, commit
39ec7de7092b ("macvtap: fix uninitialized access on
TUNSETIFF") changed the variable u from unsigned int to
unsigned short and added some ORing logic for the flags.
This introduced at least one regression:
- TUNSETSNDBUF supports int as its size and also uses the now
  short u as buffer - this breaks any sendbuf size > 64k

Let's change u back to unsigned int, keep the ORing and
handle the overwrite issue with casts and masking.

Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: David S. Miller <davem@...emloft.net>
Reported-by: Mark A. Peloquin
Bisected-by: Matthew Rosato <mjrosato@...ux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Fixes: 39ec7de7092b ("macvtap: fix uninitialized access on TUNSETIFF")
Cc: stable@...r.kernel.org
---
 drivers/net/macvtap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index edd7734..c33fe41 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -1060,7 +1060,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
 	void __user *argp = (void __user *)arg;
 	struct ifreq __user *ifr = argp;
 	unsigned int __user *up = argp;
-	unsigned short u;
+	unsigned int u;
 	int __user *sp = argp;
 	struct sockaddr sa;
 	int s;
@@ -1076,7 +1076,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
 		if ((u & ~MACVTAP_FEATURES) != (IFF_NO_PI | IFF_TAP))
 			ret = -EINVAL;
 		else
-			q->flags = (q->flags & ~MACVTAP_FEATURES) | u;
+			q->flags = (q->flags & ~MACVTAP_FEATURES) | (short) u;
 
 		return ret;
 
@@ -1089,9 +1089,8 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
 		}
 
 		ret = 0;
-		u = q->flags;
 		if (copy_to_user(&ifr->ifr_name, vlan->dev->name, IFNAMSIZ) ||
-		    put_user(u, &ifr->ifr_flags))
+		    put_user((short) q->flags, &ifr->ifr_flags))
 			ret = -EFAULT;
 		macvtap_put_vlan(vlan);
 		rtnl_unlock();
-- 
2.3.0

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