[PATCH 4.14 05/11] net: Fix zero-copy head len calculation.

Greg Kroah-Hartman
2021-08-06T08:17:35Z

From: Pravin B Shelar <pshelar@ovn.org>

[ Upstream commit a17ad0961706244dce48ec941f7e476a38c0e727 ]

In some cases skb head could be locked and entire header
data is pulled from skb. When skb_zerocopy() called in such cases,
following BUG is triggered. This patch fixes it by copying entire
skb in such cases.
This could be optimized incase this is performance bottleneck.

---8<---
kernel BUG at net/core/skbuff.c:2961!
invalid opcode: 0000 [#1] SMP PTI
CPU: 2 PID: 0 Comm: swapper/2 Tainted: G OE 5.4.0-77-generic #86-Ubuntu
Hardware name: OpenStack Foundation OpenStack Nova, BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:skb_zerocopy+0x37a/0x3a0
RSP: 0018:ffffbcc70013ca38 EFLAGS: 00010246
Call Trace:
<IRQ>
queue_userspace_packet+0x2af/0x5e0 [openvswitch]
ovs_dp_upcall+0x3d/0x60 [openvswitch]
ovs_dp_process_packet+0x125/0x150 [openvswitch]
ovs_vport_receive+0x77/0xd0 [openvswitch]
netdev_port_receive+0x87/0x130 [openvswitch]
netdev_frame_hook+0x4b/0x60 [openvswitch]
__netif_receive_skb_core+0x2b4/0xc90
__netif_receive_skb_one_core+0x3f/0xa0
__netif_receive_skb+0x18/0x60
process_backlog+0xa9/0x160
net_rx_action+0x142/0x390
__do_softirq+0xe1/0x2d6
irq_exit+0xae/0xb0
do_IRQ+0x5a/0xf0
common_interrupt+0xf/0xf

Code that triggered BUG:
int
skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
{
int i, j = 0;
int plen = 0; /* length of skb->head fragment */
int ret;
struct page *page;
unsigned int offset;

BUG_ON(!from->head_frag && !hlen);

Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/skbuff.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 18dc8524e525..a278258e68cb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2702,8 +2702,11 @@ skb_zerocopy_headlen(const struct sk_buff *from)

if (!from->head_frag ||
skb_headlen(from) < L1_CACHE_BYTES ||
- skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS)
+ skb_shinfo(from)->nr_frags >= MAX_SKB_FRAGS) {
hlen = skb_headlen(from);
+ if (!hlen)
+ hlen = from->len;
+ }

if (skb_has_frag_list(from))
hlen = from->len;
--
2.30.2