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[97.115.113.19]) by smtp.gmail.com with ESMTPSA id j14sm3349397pfe.10.2019.05.30.10.23.29 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 May 2019 10:23:29 -0700 (PDT) Subject: Re: [PATCHv2 net] net: ip6_gre: access skb data after skb_cow_head() To: William Tu , netdev@vger.kernel.org References: <1559235580-31747-1-git-send-email-u9012063@gmail.com> From: Gregory Rose Message-ID: Date: Thu, 30 May 2019 10:23:27 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <1559235580-31747-1-git-send-email-u9012063@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 > Signed-off-by: William Tu > --- > 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 Reviewed-by: Greg Rose