linux-kernel - [PATCH 3.2 008/149] tun: signedness bug in tun_get

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Message-ID: <lsq.1382345188.551263273@decadent.org.uk>
Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "David S. Miller" <davem@...emloft.net>,
	"Dan Carpenter" <dan.carpenter@...cle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	"Neil Horman" <nhorman@...driver.com>
Subject: [PATCH 3.2 008/149] tun: signedness bug in tun_get_user()

3.2.52-rc1 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: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/tun.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f4c5de6..ee1aab0 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -614,8 +614,9 @@ static ssize_t tun_get_user(struct tun_struct *tun,
 	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;
@@ -623,8 +624,9 @@ static ssize_t tun_get_user(struct tun_struct *tun,
 	}
 
 	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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