On 5/30/2019 9:59 AM, William Tu wrote:
When increases the headroom, skb's data pointer might get re-allocated. As a result, the skb->data before the skb_cow_head becomes a dangling pointer, and dereferences to daddr causes general protection fault at the following line in __gre6_xmit(): if (dev->header_ops && dev->type == ARPHRD_IP6GRE) fl6->daddr = ((struct ipv6hdr *)skb->data)->daddr; general protection fault: 0000 [#1] SMP PTI OE 4.15.0-43-generic #146-Ubuntu Hardware name: VMware, Inc. VMware Virtual Platform 440BX Desktop Reference Platform, BIOS 6.00 07/03/2018 RIP: 0010: __gre6_xmit+0x11f/0x2c0 [openvswitch] RSP: 0018:ffffb8d5c44df6a8 EFLAGS: 00010286 RAX: 00000000ffffffea RBX: ffff8b1528a0000 RCX: 0000000000000036 RDX: ffff000000000000 RSI: 0000000000000000 RDI: ffff8db267829200 RBP: ffffb8d5c44df 700 R08: 0000000000005865 RØ9: ffffb8d5c44df724 R10: 0000000000000002 R11: 0000000000000000 R12: ffff8db267829200 R13: 0000000000000000 R14: ffffb8d5c44df 728 R15: 00000000ffffffff FS: 00007f8744df 2700(0000) GS:ffff8db27fc0000000000) knlGS:0000000000000000 CS: 0910 DS: 0000 ES: 9000 CRO: 0000000080050033 CR2: 00007f893ef92148 CR3: 0000000400462003 CR4: 00000000001626f8 Call Trace: ip6gre_tunnel_xmit+0x1cc/0x530 [openvswitch] ? skb_clone+0x58/0xc0 __ip6gre_tunnel_xmit+0x12/0x20 [openvswitch] ovs_vport_send +0xd4/0x170 [openvswitch] do_output+0x53/0x160 [openvswitch] do_execute_actions+0x9a1/0x1880 [openvswitch] Fix it by moving skb_cow_head before accessing the skb->data pointer. Fixes: 01b8d064d58b4 ("net: ip6_gre: Request headroom in __gre6_xmit()") Reported-by: Haichao Ma <haich...@vmware.com> Signed-off-by: William Tu <u9012...@gmail.com> --- v1-v2: add more details in commit message. --- net/ipv6/ip6_gre.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index 655e46b227f9..90b2b129b105 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -714,6 +714,9 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb, struct ip6_tnl *tunnel = netdev_priv(dev); __be16 protocol;+ if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen))+ return -ENOMEM; + if (dev->type == ARPHRD_ETHER) IPCB(skb)->flags = 0;@@ -722,9 +725,6 @@ static netdev_tx_t __gre6_xmit(struct sk_buff *skb,else fl6->daddr = tunnel->parms.raddr;- if (skb_cow_head(skb, dev->needed_headroom ?: tunnel->hlen))- return -ENOMEM; - /* Push GRE header. */ protocol = (dev->type == ARPHRD_ETHER) ? htons(ETH_P_TEB) : proto;
Tested-by: Greg Rose <gvrose8...@gmail.com> Reviewed-by: Greg Rose <gvrose8...@gmail.com>
