tun: signedness bug in tun_get_user()

[ 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@oracle.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2491eb28a8d209ed58ad237d897767d20893b44a..7b54f4f052d085a106dba118ad6c4d1c6e41eacb 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1076,8 +1076,9 @@ 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)) > total_len)
+               if (len < sizeof(pi))
                        return -EINVAL;
+               len -= sizeof(pi);
 
                if (memcpy_fromiovecend((void *)&pi, iv, 0, sizeof(pi)))
                        return -EFAULT;
@@ -1085,8 +1086,9 @@ 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) > total_len)
+               if (len < tun->vnet_hdr_sz)
                        return -EINVAL;
+               len -= tun->vnet_hdr_sz;
 
                if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
                        return -EFAULT;