Merge branch 'read-vnet_hdr_sz-once'

Willem de Bruijn says:

====================
read vnet_hdr_sz once

Tuntap devices allow concurrent use and update of field vnet_hdr_sz.
Read the field once to avoid TOCTOU.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 6 deletions

diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index 402618565838..c27011bbe30c 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -681,7 +681,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
         size_t linear;
 
         if (q->flags & IFF_VNET_HDR) {
-                vnet_hdr_len = q->vnet_hdr_sz;
+                vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
 
                 err = -EINVAL;
                 if (len < vnet_hdr_len)
@@ -820,7 +820,7 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
 
         if (q->flags & IFF_VNET_HDR) {
                 struct virtio_net_hdr vnet_hdr;
-                vnet_hdr_len = q->vnet_hdr_sz;
+                vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
                 if (iov_iter_count(iter) < vnet_hdr_len)
                         return -EINVAL;
 
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2cd10b26b650..bfabe180053e 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1170,9 +1170,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
         }
 
         if (tun->flags & IFF_VNET_HDR) {
-                if (len < tun->vnet_hdr_sz)
+                int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
+
+                if (len < vnet_hdr_sz)
                         return -EINVAL;
-                len -= tun->vnet_hdr_sz;
+                len -= vnet_hdr_sz;
 
                 if (!copy_from_iter_full(&gso, sizeof(gso), from))
                         return -EFAULT;
@@ -1183,7 +1185,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 
                 if (tun16_to_cpu(tun, gso.hdr_len) > len)
                         return -EINVAL;
-                iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso));
+                iov_iter_advance(from, vnet_hdr_sz - sizeof(gso));
         }
 
         if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
@@ -1335,7 +1337,7 @@ static ssize_t tun_put_user(struct tun_struct *tun,
                 vlan_hlen = VLAN_HLEN;
 
         if (tun->flags & IFF_VNET_HDR)
-                vnet_hdr_sz = tun->vnet_hdr_sz;
+                vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
 
         total = skb->len + vlan_hlen + vnet_hdr_sz;