[PATCH v1 net 3/5] ip6_vti: Pull header after checking skb->protocol in vti6_tnl_xmit().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

syzkaller demonstrated the underflow in pskb_network_may_pull()
by sending a crafted VLAN packet over the tunnel device.

Let's check skb->protocol before pulling the next header in
vti6_tnl_xmit().

WARNING: CPU: 0 PID: 722 at include/linux/skbuff.h:2740 pskb_may_pull_reason include/linux/skbuff.h:2740 [inline]
WARNING: CPU: 0 PID: 722 at include/linux/skbuff.h:2740 pskb_may_pull include/linux/skbuff.h:2756 [inline]
WARNING: CPU: 0 PID: 722 at include/linux/skbuff.h:2740 pskb_network_may_pull include/linux/skbuff.h:3077 [inline]
WARNING: CPU: 0 PID: 722 at include/linux/skbuff.h:2740 pskb_inet_may_pull include/net/ip_tunnels.h:361 [inline]
WARNING: CPU: 0 PID: 722 at include/linux/skbuff.h:2740 vti6_tnl_xmit+0x100c/0x16c0 net/ipv6/ip6_vti.c:560
Modules linked in:
CPU: 0 PID: 722 Comm: syz-executor.3 Not tainted 6.8.0-12821-g537c2e91d354-dirty #11
Hardware name: linux,dummy-virt (DT)
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : pskb_may_pull_reason include/linux/skbuff.h:2740 [inline]
pc : pskb_may_pull include/linux/skbuff.h:2756 [inline]
pc : pskb_network_may_pull include/linux/skbuff.h:3077 [inline]
pc : pskb_inet_may_pull include/net/ip_tunnels.h:361 [inline]
pc : vti6_tnl_xmit+0x100c/0x16c0 net/ipv6/ip6_vti.c:560
lr : pskb_may_pull_reason include/linux/skbuff.h:2740 [inline]
lr : pskb_may_pull include/linux/skbuff.h:2756 [inline]
lr : pskb_network_may_pull include/linux/skbuff.h:3077 [inline]
lr : pskb_inet_may_pull include/net/ip_tunnels.h:361 [inline]
lr : vti6_tnl_xmit+0x100c/0x16c0 net/ipv6/ip6_vti.c:560
sp : ffff8000a86d7280
x29: ffff8000a86d73e0 x28: ffff7000150dae64 x27: ffff8000a86d7320
x26: ffff00004fdd0010 x25: dfff800000000000 x24: 00000000fffffff6
x23: ffff00000a0ae478 x22: ffff00000a0ae498 x21: ffff00000a0ae474
x20: ffff00000a0ae3c0 x19: ffff0000178d6000 x18: ffff800086d72d10
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000001
x14: 1fffe0000958b817 x13: 0000000000000000 x12: 0000000000000001
x11: 0000000000040000 x10: 0000000000000b8a x9 : ffff80008e699000
x8 : 0000000000000b8b x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff8000a86d6c98 x4 : ffff800086d8b120 x3 : ffff800083f7f7d4
x2 : 0000000000000001 x1 : 00000000fffffff6 x0 : 0000000000000000
Call trace:
 pskb_may_pull_reason include/linux/skbuff.h:2740 [inline]
 pskb_may_pull include/linux/skbuff.h:2756 [inline]
 pskb_network_may_pull include/linux/skbuff.h:3077 [inline]
 pskb_inet_may_pull include/net/ip_tunnels.h:361 [inline]
 vti6_tnl_xmit+0x100c/0x16c0 net/ipv6/ip6_vti.c:560
 __netdev_start_xmit include/linux/netdevice.h:4903 [inline]
 netdev_start_xmit include/linux/netdevice.h:4917 [inline]
 xmit_one net/core/dev.c:3531 [inline]
 dev_hard_start_xmit+0x1a0/0x370 net/core/dev.c:3547
 __dev_queue_xmit+0x12e8/0x2b04 net/core/dev.c:4335
 dev_queue_xmit include/linux/netdevice.h:3091 [inline]
 packet_xmit+0x6c/0x31c net/packet/af_packet.c:276
 packet_snd net/packet/af_packet.c:3081 [inline]
 packet_sendmsg+0x3818/0x4e50 net/packet/af_packet.c:3113
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 __sys_sendto+0x324/0x470 net/socket.c:2191
 __do_sys_sendto net/socket.c:2203 [inline]
 __se_sys_sendto net/socket.c:2199 [inline]
 __arm64_sys_sendto+0xd8/0xf8 net/socket.c:2199
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:133
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:152
 el0_svc+0x30/0x78 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598

Reported-by: syzkaller <syzkaller@googlegroups.com>
Fixes: cb9f1b783850 ("ip: validate header length on virtual device xmit")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/ipv6/ip6_vti.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 7f4f976aa24a..98c738eb6166 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -557,13 +557,13 @@ vti6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 	struct flowi fl;
 	int ret;
 
-	if (!pskb_inet_may_pull(skb))
-		goto tx_err;
-
 	memset(&fl, 0, sizeof(fl));
 
 	switch (skb->protocol) {
 	case htons(ETH_P_IPV6):
+		if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
+			goto tx_err;
+
 		if ((t->parms.proto != IPPROTO_IPV6 && t->parms.proto != 0) ||
 		    vti6_addr_conflict(t, ipv6_hdr(skb)))
 			goto tx_err;
@@ -572,6 +572,9 @@ vti6_tnl_xmit(struct sk_buff *skb, struct net_device *dev)
 		xfrm_decode_session(dev_net(dev), skb, &fl, AF_INET6);
 		break;
 	case htons(ETH_P_IP):
+		if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
+			goto tx_err;
+
 		memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 		xfrm_decode_session(dev_net(dev), skb, &fl, AF_INET);
 		break;
-- 
2.30.2