[Devel] [PATCH RHEL7 COMMIT] ms/ipv6: allocate enough headroom in ip6_finish_output2()

[Vasily Averin]

The commit is pushed to "branch-rh7-3.10.0-1160.41.1.vz7.183.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.41.1.vz7.183.3
------>
commit 54a2223f8be9a40306eb3f2b5ede9a9748ffa737
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Tue Sep 14 09:56:15 2021 +0300

    ms/ipv6: allocate enough headroom in ip6_finish_output2()
    
    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
    
    [backport of first version of upstream patch,
     patch version included finally to upstream requires some other changes]
    Link: https://lkml.org/lkml/2021/7/7/469
    https://jira.sw.ru/browse/PSBM-130907
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/ipv6/ip6_output.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index ca42e2c..6c2082d 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -60,6 +60,7 @@ static int ip6_finish_output2(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);
 	const struct in6_addr *nexthop;
 	struct neighbour *neigh;
 	int ret;
@@ -67,6 +68,20 @@ static int ip6_finish_output2(struct sock *sk, struct sk_buff *skb)
 	skb->protocol = htons(ETH_P_IPV6);
 	skb->dev = dev;
 
+	/* Be paranoid, rather than too clever. */
+	if (unlikely(skb_headroom(skb) < hh_len && dev->header_ops)) {
+		struct sk_buff *skb2;
+
+		skb2 = skb_realloc_headroom(skb, hh_len);
+		if (skb2 == NULL) {
+			kfree_skb(skb);
+			return -ENOMEM;
+		}
+		if (skb->sk)
+			skb_set_owner_w(skb2, skb->sk);
+		consume_skb(skb);
+		skb = skb2;
+	}
 	if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr)) {
 		struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));