[PATCH 4.4 40/78] s390/qeth: no ETH header for outbound AF_IUCV

From: Greg Kroah-Hartman
Date: Fri Dec 22 2017 - 03:51:05 EST

4.4-stable review patch. If anyone has any objections, please let me know.


From: Julian Wiedmann <jwi@xxxxxxxxxxxxxxxxxx>

[ Upstream commit acd9776b5c45ef02d1a210969a6fcc058afb76e3 ]

With AF_IUCV traffic, the skb passed to hard_start_xmit() has a 14 byte
slot at skb->data, intended for an ETH header. qeth_l3_fill_af_iucv_hdr()
fills this ETH header... and then immediately moves it to the
skb's headroom, where it disappears and is never seen again.

But it's still possible for us to return NETDEV_TX_BUSY after the skb has
been modified. Since we didn't get a private copy of the skb, the next
time the skb is delivered to hard_start_xmit() it no longer has the
expected layout (we moved the ETH header to the headroom, so skb->data
now starts at the IUCV_TRANS header). So when qeth_l3_fill_af_iucv_hdr()
does another round of rebuilding, the resulting qeth header ends up
all wrong. On transmission, the buffer is then rejected by
the HiperSockets device with SBALF15 = x'04'.
When this error is passed back to af_iucv as TX_NOTIFY_UNREACHABLE, it
tears down the offending socket.

As the ETH header for AF_IUCV serves no purpose, just align the code to
what we do for IP traffic on L3 HiperSockets: keep the ETH header at
skb->data, and pass down data_offset = ETH_HLEN to qeth_fill_buffer().
When mapping the payload into the SBAL elements, the ETH header is then
stripped off. This avoids the skb manipulations in
qeth_l3_fill_af_iucv_hdr(), and any buffer re-entering hard_start_xmit()
after NETDEV_TX_BUSY is now processed properly.

Signed-off-by: Julian Wiedmann <jwi@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ursula Braun <ubraun@xxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
drivers/s390/net/qeth_l3_main.c | 15 ++++-----------
1 file changed, 4 insertions(+), 11 deletions(-)

--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2680,17 +2680,13 @@ static void qeth_l3_fill_af_iucv_hdr(str
char daddr[16];
struct af_iucv_trans_hdr *iucv_hdr;

- skb_pull(skb, 14);
- card->dev->header_ops->create(skb, card->dev, 0,
- card->dev->dev_addr, card->dev->dev_addr,
- card->dev->addr_len);
- skb_pull(skb, 14);
- iucv_hdr = (struct af_iucv_trans_hdr *)skb->data;
memset(hdr, 0, sizeof(struct qeth_hdr));
hdr->hdr.l3.id = QETH_HEADER_TYPE_LAYER3;
hdr->hdr.l3.ext_flags = 0;
- hdr->hdr.l3.length = skb->len;
+ hdr->hdr.l3.length = skb->len - ETH_HLEN;
hdr->hdr.l3.flags = QETH_HDR_IPV6 | QETH_CAST_UNICAST;
+ iucv_hdr = (struct af_iucv_trans_hdr *) (skb->data + ETH_HLEN);
memset(daddr, 0, sizeof(daddr));
daddr[0] = 0xfe;
daddr[1] = 0x80;
@@ -2873,10 +2869,7 @@ static int qeth_l3_hard_start_xmit(struc
if ((card->info.type == QETH_CARD_TYPE_IQD) && (!large_send) &&
(skb_shinfo(skb)->nr_frags == 0)) {
new_skb = skb;
- if (new_skb->protocol == ETH_P_AF_IUCV)
- data_offset = 0;
- else
- data_offset = ETH_HLEN;
+ data_offset = ETH_HLEN;
hdr = kmem_cache_alloc(qeth_core_header_cache, GFP_ATOMIC);
if (!hdr)
goto tx_drop;