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Subject[PATCH 3.2 190/199] tun: Fix TUN_PKT_STRIP setting
3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Herbert Xu <herbert@gondor.apana.org.au>

commit 2eb783c43e7cf807a45899c10ed556b6dc116625 upstream.

We set the flag TUN_PKT_STRIP if the user buffer provided is too
small to contain the entire packet plus meta-data. However, this
has been broken ever since we added GSO meta-data. VLAN acceleration
also has the same problem.

This patch fixes this by taking both into account when setting the
TUN_PKT_STRIP flag.

The fact that this has been broken for six years without anyone
realising means that nobody actually uses this flag.

Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
- No VLAN acceleration support
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/tun.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -767,12 +767,16 @@ static ssize_t tun_put_user(struct tun_s
{
struct tun_pi pi = { 0, skb->protocol };
ssize_t total = 0;
+ int vnet_hdr_sz = 0;
+
+ if (tun->flags & TUN_VNET_HDR)
+ vnet_hdr_sz = tun->vnet_hdr_sz;

if (!(tun->flags & TUN_NO_PI)) {
if ((len -= sizeof(pi)) < 0)
return -EINVAL;

- if (len < skb->len) {
+ if (len < skb->len + vnet_hdr_sz) {
/* Packet will be striped */
pi.flags |= TUN_PKT_STRIP;
}
@@ -782,9 +786,9 @@ static ssize_t tun_put_user(struct tun_s
total += sizeof(pi);
}

- if (tun->flags & TUN_VNET_HDR) {
+ if (vnet_hdr_sz) {
struct virtio_net_hdr gso = { 0 }; /* no info leak */
- if ((len -= tun->vnet_hdr_sz) < 0)
+ if ((len -= vnet_hdr_sz) < 0)
return -EINVAL;

if (skb_is_gso(skb)) {
@@ -827,7 +831,7 @@ static ssize_t tun_put_user(struct tun_s
if (unlikely(memcpy_toiovecend(iv, (void *)&gso, total,
sizeof(gso))))
return -EFAULT;
- total += tun->vnet_hdr_sz;
+ total += vnet_hdr_sz;
}

len = min_t(int, skb->len, len);
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