Subject: Re: ipv6: oops in datagram.c line 260

From: Steffen Klassert <[email-masked]>
Date: Mon, 26 Jan 2015 09:35:13 +0100

On Tue, Jan 06, 2015 at 05:01:13PM +0100, Hannes Frederic Sowa wrote:
> On Mi, 2014-12-24 at 21:42 +0800, Chris Ruehl wrote:
> > [447604.244357] ipv6_pinfo is NULL
> > [447604.273733] ------------[ cut here ]------------
> > [447604.303628] WARNING: CPU: 7 PID: 0 at net/ipv6/datagram.c:262 
> > ipv6_local_error+0x16b/0x1a0()
> > [[...]]
> > [last unloaded: ipmi_si]
> > [447605.087999] CPU: 7 PID: 0 Comm: swapper/7 Not tainted 3.14.27 #11
> > [447605.139687] Hardware name: Dell Inc. PowerEdge R420/0CN7CM, BIOS 2.3.3 
> > 07/10/2014
> > [447605.242931]  0000000000000009 ffff8806172e3b48 ffffffff815ffd58 0000000000000000
> > [447605.349130]  ffff8806172e3b80 ffffffff81043c23 ffff8800a16322e8 ffff880037daa1c0
> > [447605.459659]  ffff88000b026800 0000000000000000 ffff880037daa4b8 ffff8806172e3b90
> > [447605.576385] Call Trace:
> > [447605.634243]  <IRQ>  [<ffffffff815ffd58>] dump_stack+0x45/0x56
> > [447605.692870]  [<ffffffff81043c23>] warn_slowpath_common+0x73/0x90
> > [447605.751097]  [<ffffffff81043cf5>] warn_slowpath_null+0x15/0x20
> > [447605.808000]  [<ffffffff815da6db>] ipv6_local_error+0x16b/0x1a0
> > [447605.863821]  [<ffffffff815e29d0>] xfrm6_local_error+0x60/0x90
> > [447605.918493]  [<ffffffff8150b485>] ? skb_dequeue+0x15/0x70
> > [447605.971871]  [<ffffffff815a6cc1>] xfrm_local_error+0x51/0x70
> > [447606.024218]  [<ffffffff8159ca15>] xfrm4_extract_output+0x75/0xb0
> > [447606.075630]  [<ffffffff815a6c5a>] xfrm_inner_extract_output+0x6a/0x80
> > [447606.126055]  [<ffffffff815e27a2>] xfrm6_prepare_output+0x12/0x60
> > [447606.175310]  [<ffffffff815a6ed0>] xfrm_output_resume+0x1f0/0x370
> > [447606.223406]  [<ffffffff8151a486>] ? skb_checksum_help+0x76/0x190
> > [447606.270572]  [<ffffffff815a709b>] xfrm_output+0x3b/0xf0
> > [447606.316454]  [<ffffffff815e2ae0>] ? xfrm6_extract_output+0xe0/0xe0
> > [447606.361803]  [<ffffffff815e2af7>] xfrm6_output_finish+0x17/0x20
> > [447606.406053]  [<ffffffff8159cad6>] xfrm4_output+0x46/0x80
> > [447606.448694]  [<ffffffff81550a80>] ip_local_out+0x20/0x30
> > [447606.489952]  [<ffffffff81550dd5>] ip_queue_xmit+0x135/0x3c0
> > [447606.530017]  [<ffffffff815672e1>] tcp_transmit_skb+0x461/0x8c0
> > [447606.569362]  [<ffffffff8156786e>] tcp_write_xmit+0x12e/0xb20
> > [447606.607876]  [<ffffffff815669ff>] ? tcp_current_mss+0x4f/0x70
> > [447606.645723]  [<ffffffff8156b320>] ? tcp_write_timer_handler+0x1b0/0x1b0
> > [447606.682837]  [<ffffffff81569487>] tcp_send_loss_probe+0x37/0x1f0
> > [447606.719000]  [<ffffffff8156b320>] ? tcp_write_timer_handler+0x1b0/0x1b0
> > [447606.754537]  [<ffffffff8156b1bb>] tcp_write_timer_handler+0x4b/0x1b0
> > [447606.789266]  [<ffffffff8156b320>] ? tcp_write_timer_handler+0x1b0/0x1b0
> > [447606.823242]  [<ffffffff8156b378>] tcp_write_timer+0x58/0x60
> > [447606.856047]  [<ffffffff8104e848>] call_timer_fn.isra.32+0x18/0x80
> > [447606.888029]  [<ffffffff8104ea1a>] run_timer_softirq+0x16a/0x200
> > [447606.920224]  [<ffffffff81047efc>] __do_softirq+0xec/0x250
> > [447606.951850]  [<ffffffff810482f5>] irq_exit+0xf5/0x100
> > [447606.982665]  [<ffffffff8102bc6f>] smp_apic_timer_interrupt+0x3f/0x50
> > [447607.014382]  [<ffffffff8160d98a>] apic_timer_interrupt+0x6a/0x70
> > [447607.046175]  <EOI>  [<ffffffff8104f336>] ? get_next_timer_interrupt+0x1d6/0x250
> > [447607.111311]  [<ffffffff814d45a7>] ? cpuidle_enter_state+0x47/0xc0
> > [447607.145850]  [<ffffffff814d45a3>] ? cpuidle_enter_state+0x43/0xc0
> > [447607.179625]  [<ffffffff814d46b6>] cpuidle_idle_call+0x96/0x130
> > [447607.213531]  [<ffffffff8100b909>] arch_cpu_idle+0x9/0x20
> > [447607.247052]  [<ffffffff810925ba>] cpu_startup_entry+0xda/0x1d0
> > [447607.280775]  [<ffffffff81029d22>] start_secondary+0x212/0x2c0
> > [447607.314555] ---[ end trace 6ff3826b6e4fdf67 ]---
> > 
> 
> Thanks for the report!
> 
> xfrm6_output_finish unconditionally resets skb->protocol so we try to
> dispatch to the IPv6 handler, even though tcp just sends an IPv4 packet.
> 

Looks like we can postpone the setting of skb->protocol to the
xfrm{4,6}_prepare_output() functions where we finally switch to
outer mode.

This has two implications:

- We reset skb->protocol only for tunnel modes, should be ok.

- This affects the xfrm_output_gso() codepath on interfamily
  tunnels. skb_mac_gso_segment() dispatches to the gso_segment()
  callback functions via skb->protocol. So we dispatch to
  the gso_segment() function of the outer mode what looks
  wrong to me. If we postpone the setting of skb->protocol
  to the xfrm{4,6}_prepare_output() we dispatch to inner mode
  here.

Unfortunately I was not able to reproduce the problem on our test
setup. Chris could you try if the the patch below fixes your
problem?

Subject: [PATCH RFC] xfrm: Fix local error reporting crash with interfamily
 tunnels

We set the outer mode protocol too early. As a result, the
local error handler might dispatch to the wrong	address family
and report the error to a wrong socket type. We fix this by
seting the outer protocol to the skb after we accessed the
inner mode for the last time, right before we do the atcual
encapsulation where we switch finally to the outer mode.

Reported-by: Chris Ruehl <[email-masked]>
Signed-off-by: Steffen Klassert <[email-masked]>
---
 net/ipv4/xfrm4_output.c | 2 +-
 net/ipv6/xfrm6_output.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
index d5f6bd9..dab7381 100644
--- a/net/ipv4/xfrm4_output.c
+++ b/net/ipv4/xfrm4_output.c
@@ -63,6 +63,7 @@ int xfrm4_prepare_output(struct xfrm_state *x, struct sk_buff *skb)
 		return err;
 
 	IPCB(skb)->flags |= IPSKB_XFRM_TUNNEL_SIZE;
+	skb->protocol = htons(ETH_P_IP);
 
 	return x->outer_mode->output2(x, skb);
 }
@@ -71,7 +72,6 @@ EXPORT_SYMBOL(xfrm4_prepare_output);
 int xfrm4_output_finish(struct sk_buff *skb)
 {
 	memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
-	skb->protocol = htons(ETH_P_IP);
 
 #ifdef CONFIG_NETFILTER
 	IPCB(skb)->flags |= IPSKB_XFRM_TRANSFORMED;
diff --git a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
index ca3f29b..010f8bd 100644
--- a/net/ipv6/xfrm6_output.c
+++ b/net/ipv6/xfrm6_output.c
@@ -114,6 +114,7 @@ int xfrm6_prepare_output(struct xfrm_state *x, struct sk_buff *skb)
 		return err;
 
 	skb->ignore_df = 1;
+	skb->protocol = htons(ETH_P_IPV6);
 
 	return x->outer_mode->output2(x, skb);
 }
@@ -122,7 +123,6 @@ EXPORT_SYMBOL(xfrm6_prepare_output);
 int xfrm6_output_finish(struct sk_buff *skb)
 {
 	memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
-	skb->protocol = htons(ETH_P_IPV6);
 
 #ifdef CONFIG_NETFILTER
 	IP6CB(skb)->flags |= IP6SKB_XFRM_TRANSFORMED;
-- 
1.9.1