linux-kernel - [ 10/23] tun: signedness bug in tun_get

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Date:	Thu, 12 Sep 2013 10:45:06 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 10/23] tun: signedness bug in tun_get_user()

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@...cle.com>

[ Upstream commit 15718ea0d844e4816dbd95d57a8a0e3e264ba90e ]

The recent fix d9bf5f1309 "tun: compare with 0 instead of total_len" is
not totally correct.  Because "len" and "sizeof()" are size_t type, that
means they are never less than zero.

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
Acked-by: Neil Horman <nhorman@...driver.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/tun.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -615,8 +615,9 @@ static ssize_t tun_get_user(struct tun_s
 	int offset = 0;
 
 	if (!(tun->flags & TUN_NO_PI)) {
-		if ((len -= sizeof(pi)) > count)
+		if (len < sizeof(pi))
 			return -EINVAL;
+		len -= sizeof(pi);
 
 		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
 			return -EFAULT;
@@ -624,8 +625,9 @@ static ssize_t tun_get_user(struct tun_s
 	}
 
 	if (tun->flags & TUN_VNET_HDR) {
-		if ((len -= tun->vnet_hdr_sz) > count)
+		if (len < tun->vnet_hdr_sz)
 			return -EINVAL;
+		len -= tun->vnet_hdr_sz;
 
 		if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
 			return -EFAULT;


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