netdev - [patch] tun: signedness bug in tun_get

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Message-ID: <20130815125257.GA16932@elgon.mountain>
Date:	Thu, 15 Aug 2013 15:52:57 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Neil Horman <nhorman@...driver.com>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [patch] tun: signedness bug in tun_get_user()

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>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index af987f0..7ed13cc 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -977,8 +977,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	u32 rxhash;
 
 	if (!(tun->flags & TUN_NO_PI)) {
-		if ((len -= sizeof(pi)) < 0)
+		if (len < sizeof(pi))
 			return -EINVAL;
+		len -= sizeof(pi);
 
 		if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
 			return -EFAULT;
@@ -986,8 +987,9 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	}
 
 	if (tun->flags & TUN_VNET_HDR) {
-		if ((len -= tun->vnet_hdr_sz) < 0)
+		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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