When TEE target mirrors traffic to another interface, sk_buff may
not have enough headroom to be processed correctly.
ip_finish_output2() detect this situation for ipv4 and allocates
new skb with enogh headroom. However ipv6 lacks this logic in
ip_finish_output2 and it leads to skb_under_panic:
skbuff: skb_under_panic: text:ffffffffc0866ad4 len:96 put:24
head:ffff97be85e31800 data:ffff97be85e317f8 tail:0x58 end:0xc0 dev:gre0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:110!
invalid opcode: 0000 [#1] SMP PTI
CPU: 2 PID: 393 Comm: kworker/2:2 Tainted: G OE 5.13.0 #13
Hardware name: Virtuozzo KVM, BIOS 1.11.0-2.vz7.4 04/01/2014
Workqueue: ipv6_addrconf addrconf_dad_work
RIP: 0010:skb_panic+0x48/0x4a
Call Trace:
skb_push.cold.111+0x10/0x10
ipgre_header+0x24/0xf0 [ip_gre]
neigh_connected_output+0xae/0xf0
ip6_finish_output2+0x1a8/0x5a0
ip6_output+0x5c/0x110
nf_dup_ipv6+0x158/0x1000 [nf_dup_ipv6]
tee_tg6+0x2e/0x40 [xt_TEE]
ip6t_do_table+0x294/0x470 [ip6_tables]
nf_hook_slow+0x44/0xc0
nf_hook.constprop.34+0x72/0xe0
ndisc_send_skb+0x20d/0x2e0
ndisc_send_ns+0xd1/0x210
addrconf_dad_work+0x3c8/0x540
process_one_work+0x1d1/0x370
worker_thread+0x30/0x390
kthread+0x116/0x130
ret_from_fork+0x22/0x30
This patch implement new helper that tries to expand headroom on current skb,
if it is not possible (shared_skb) -- creates new one.
v2 open questions:
- currently helper name skb_expand_head is bad
and should be changed to better one. Any suggestions?
- proper location for new helper:
in net/core/skbuff.c right below skb_realloc_headroom() ?
- is it acceptable to free original skb inside helper ?
Is it probably required to keep it in caller instead?
Signed-off-by: Vasily Averin <[email protected]>
---
net/ipv6/ip6_output.c | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index ff4f9eb..6c5f85f 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -56,14 +56,48 @@
#include <net/lwtunnel.h>
#include <net/ip_tunnels.h>
+static inline struct sk_buff *skb_expand_head(struct sk_buff *skb, int delta)
+{
+ /* pskb_expand_head() might crash, if skb is shared */
+ if (skb_shared(skb)) {
+ struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
+
+ if (likely(nskb)) {
+ if (skb->sk)
+ skb_set_owner_w(skb, skb->sk);
+ consume_skb(skb);
+ } else {
+ kfree_skb(skb);
+ }
+ skb = nskb;
+ }
+ if (skb &&
+ pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
+ kfree_skb(skb);
+ skb = NULL;
+ }
+ return skb;
+}
+
static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *skb)
{
struct dst_entry *dst = skb_dst(skb);
struct net_device *dev = dst->dev;
+ unsigned int hh_len = LL_RESERVED_SPACE(dev);
+ int delta = hh_len - skb_headroom(skb);
const struct in6_addr *nexthop;
struct neighbour *neigh;
int ret;
+ /* Be paranoid, rather than too clever. */
+ if (unlikely(delta > 0) && dev->header_ops)
+ skb = skb_expand_head(skb, delta);
+
+ if (!skb) {
+ IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTDISCARDS);
+ return -ENOMEM;
+ }
+
if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr)) {
struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
--
1.8.3.1
Please do not use inline in foo.c files, let the compiler decde.
Thank you.
Dear David,
I'm happy to hear you again.
On 7/9/21 8:58 PM, David Miller wrote:
> Please do not use inline in foo.c files, let the compiler decde.
Thank you for the hint, I did not know it, and will follow him next time.
This time I'm going to move this helper somewhere anyway:
either to net/core/skbuff.c as exported function where it will lost inline anyway,
or to include/linux/skbuff.h where inline is (it seems?) acceptable.
Could you please help me to find better name for this helper?
I would like to change its current name: 'skb_expand_head' looks very similar
to widely used 'pskb_expand_head' but have different semantic.
I afraid they can be accidentally misused in future.
Thank you,
Vasily Averin.