On Mon, Aug 31, 2015 at 4:44 PM, Tom Herbert [off-list ref] wrote:

On Mon, Aug 31, 2015 at 3:55 PM, Pravin B Shelar [off-list ref] wrote:

quoted

VXLAN device can receive skb with checksum partial. But the checksum
offset could be in outer header which is pulled on receive. Such skb
can cause the panic when checksum is calculated on skb. Following patch
fixes the bug by setting checksum unnecessary while pulling outer header.

---8<---
[ 13.800141] RIP: 0010:[<ffffffff81518034>] [<ffffffff81518034>] skb_checksum_help+0x144/0x150
[ 13.800141] RSP: 0000:ffff88011fd83940 EFLAGS: 00010292
[ 13.800141] RAX: 0000000000000042 RBX: ffff880114dd56c0 RCX: ffff8801188d9580
...
...
[ 13.852308] Call Trace:
[ 13.852308] <IRQ>
[ 13.852308] [<ffffffffa0164c28>] queue_userspace_packet+0x408/0x470 [openvswitch]
[ 13.852308] [<ffffffffa016614d>] ovs_dp_upcall+0x5d/0x60 [openvswitch]
[ 13.852308] [<ffffffffa0166236>] ovs_dp_process_packet_with_key+0xe6/0x100 [openvswitch]
[ 13.852308] [<ffffffffa016629b>] ovs_dp_process_received_packet+0x4b/0x80 [openvswitch]
[ 13.852308] [<ffffffffa016c51a>] ovs_vport_receive+0x2a/0x30 [openvswitch]
[ 13.852308] [<ffffffffa0171383>] vxlan_rcv+0x53/0x60 [openvswitch]
[ 13.852308] [<ffffffffa01734cb>] vxlan_udp_encap_recv+0x8b/0xf0 [openvswitch]
[ 13.852308] [<ffffffff8157addc>] udp_queue_rcv_skb+0x2dc/0x3b0
[ 13.852308] [<ffffffff8157b56f>] __udp4_lib_rcv+0x1cf/0x6c0
[ 13.852308] [<ffffffff8157ba7a>] udp_rcv+0x1a/0x20
[ 13.852308] [<ffffffff8154fdbd>] ip_local_deliver_finish+0xdd/0x280
[ 13.852308] [<ffffffff81550128>] ip_local_deliver+0x88/0x90
[ 13.852308] [<ffffffff8154fa7d>] ip_rcv_finish+0x10d/0x370
[ 13.852308] [<ffffffff81550365>] ip_rcv+0x235/0x300
[ 13.852308] [<ffffffff8151ba1d>] __netif_receive_skb+0x55d/0x620
[ 13.852308] [<ffffffff8151c360>] netif_receive_skb+0x80/0x90
[ 13.852308] [<ffffffff81459935>] virtnet_poll+0x555/0x6f0
[ 13.852308] [<ffffffff8151cd04>] net_rx_action+0x134/0x290
[ 13.852308] [<ffffffff810683d8>] __do_softirq+0xa8/0x210
[ 13.852308] [<ffffffff8162fe6c>] call_softirq+0x1c/0x30
[ 13.852308] [<ffffffff810161a5>] do_softirq+0x65/0xa0
[ 13.852308] [<ffffffff810687be>] irq_exit+0x8e/0xb0
[ 13.852308] [<ffffffff81630733>] do_IRQ+0x63/0xe0
[ 13.852308] [<ffffffff81625f2e>] common_interrupt+0x6e/0x6e
[ 13.852308] <EOI>
[ 13.852308] [<ffffffff8162dc02>] ? system_call_fastpath+0x16/0x1b

Reported-by: Anupam Chanda <redacted>
Signed-off-by: Pravin B Shelar <redacted>
---
 include/linux/skbuff.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9b88536..6238e9f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -2601,6 +2601,9 @@ static inline void skb_postpull_rcsum(struct sk_buff *skb,
 {
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
+       else if (skb->ip_summed == CHECKSUM_PARTIAL &&
+                skb_checksum_start_offset(skb) <= len)
+               skb->ip_summed = CHECKSUM_UNNECESSARY;

No, this isn't right. We should never be converting CHECKSUM_PARTIAL
into CHECKSUM_UNNECESSARY.

But checksum is valid for inner packet. So I do not see any other
appropriate checksum flag here. Can you suggest another flag which is
better suited?