net: add vlan_get_protocol_and_depth() helper

Before blamed commit, pskb_may_pull() was used instead
of skb_header_pointer() in __vlan_get_protocol() and friends.

Few callers depended on skb->head being populated with MAC header,
syzbot caught one of them (skb_mac_gso_segment())

Add vlan_get_protocol_and_depth() to make the intent clearer
and use it where sensible.

This is a more generic fix than commit e9d3f809
("net/af_packet: make sure to pull mac header") which was
dealing with a similar issue.

kernel BUG at include/linux/skbuff.h:2655 !
invalid opcode: 0000 [#1] SMP KASAN
CPU: 0 PID: 1441 Comm: syz-executor199 Not tainted 6.1.24-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
RIP: 0010:__skb_pull include/linux/skbuff.h:2655 [inline]
RIP: 0010:skb_mac_gso_segment+0x68f/0x6a0 net/core/gro.c:136
Code: fd 48 8b 5c 24 10 44 89 6b 70 48 c7 c7 c0 ae 0d 86 44 89 e6 e8 a1 91 d0 00 48 c7 c7 00 af 0d 86 48 89 de 31 d2 e8 d1 4a e9 ff <0f> 0b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 48 89 e5 41
RSP: 0018:ffffc90001bd7520 EFLAGS: 00010286
RAX: ffffffff8469736a RBX: ffff88810f31dac0 RCX: ffff888115a18b00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90001bd75e8 R08: ffffffff84697183 R09: fffff5200037adf9
R10: 0000000000000000 R11: dffffc0000000001 R12: 0000000000000012
R13: 000000000000fee5 R14: 0000000000005865 R15: 000000000000fed7
FS: 000055555633f300(0000) GS:ffff8881f6a00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 0000000116fea000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
[<ffffffff847018dd>] __skb_gso_segment+0x32d/0x4c0 net/core/dev.c:3419
[<ffffffff8470398a>] skb_gso_segment include/linux/netdevice.h:4819 [inline]
[<ffffffff8470398a>] validate_xmit_skb+0x3aa/0xee0 net/core/dev.c:3725
[<ffffffff84707042>] __dev_queue_xmit+0x1332/0x3300 net/core/dev.c:4313
[<ffffffff851a9ec7>] dev_queue_xmit+0x17/0x20 include/linux/netdevice.h:3029
[<ffffffff851b4a82>] packet_snd net/packet/af_packet.c:3111 [inline]
[<ffffffff851b4a82>] packet_sendmsg+0x49d2/0x6470 net/packet/af_packet.c:3142
[<ffffffff84669a12>] sock_sendmsg_nosec net/socket.c:716 [inline]
[<ffffffff84669a12>] sock_sendmsg net/socket.c:736 [inline]
[<ffffffff84669a12>] __sys_sendto+0x472/0x5f0 net/socket.c:2139
[<ffffffff84669c75>] __do_sys_sendto net/socket.c:2151 [inline]
[<ffffffff84669c75>] __se_sys_sendto net/socket.c:2147 [inline]
[<ffffffff84669c75>] __x64_sys_sendto+0xe5/0x100 net/socket.c:2147
[<ffffffff8551d40f>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<ffffffff8551d40f>] do_syscall_64+0x2f/0x50 arch/x86/entry/common.c:80
[<ffffffff85600087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 469acedd ("vlan: consolidate VLAN parsing code and limit max parsing depth")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/tap.c

@@ -742,7 +742,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 
 	/* Move network header to the right position for VLAN tagged packets */
 	if (eth_type_vlan(skb->protocol) &&
-	    __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
+	    vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0)
 		skb_set_network_header(skb, depth);
 
 	/* copy skb_ubuf_info for callback when skb has no error */
@@ -1197,7 +1197,7 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp)
 
 	/* Move network header to the right position for VLAN tagged packets */
 	if (eth_type_vlan(skb->protocol) &&
-	    __vlan_get_protocol(skb, skb->protocol, &depth) != 0)
+	    vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0)
 		skb_set_network_header(skb, depth);
 
 	rcu_read_lock();

include/linux/if_vlan.h

@@ -637,6 +637,23 @@ static inline __be16 vlan_get_protocol(const struct sk_buff *skb)
 	return __vlan_get_protocol(skb, skb->protocol, NULL);
 }
 
+/* This version of __vlan_get_protocol() also pulls mac header in skb->head */
+static inline __be16 vlan_get_protocol_and_depth(struct sk_buff *skb,
+						 __be16 type, int *depth)
+{
+	int maclen;
+
+	type = __vlan_get_protocol(skb, type, &maclen);
+
+	if (type) {
+		if (!pskb_may_pull(skb, maclen))
+			type = 0;
+		else if (depth)
+			*depth = maclen;
+	}
+	return type;
+}
+
 /* A getter for the SKB protocol field which will handle VLAN tags consistently
  * whether VLAN acceleration is enabled or not.
  */

net/bridge/br_forward.c

@@ -42,7 +42,7 @@ int br_dev_queue_push_xmit(struct net *net, struct sock *sk, struct sk_buff *skb
 	    eth_type_vlan(skb->protocol)) {
 		int depth;
 
-		if (!__vlan_get_protocol(skb, skb->protocol, &depth))
+		if (!vlan_get_protocol_and_depth(skb, skb->protocol, &depth))
 			goto drop;
 
 		skb_set_network_header(skb, depth);

net/core/dev.c

@@ -3335,7 +3335,7 @@ __be16 skb_network_protocol(struct sk_buff *skb, int *depth)
 		type = eth->h_proto;
 	}
 
-	return __vlan_get_protocol(skb, type, depth);
+	return vlan_get_protocol_and_depth(skb, type, depth);
 }
 
 /* openvswitch calls this on rx path, so we need a different check.

net/packet/af_packet.c

@@ -1934,10 +1934,8 @@ static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
 	/* Move network header to the right position for VLAN tagged packets */
 	if (likely(skb->dev->type == ARPHRD_ETHER) &&
 	    eth_type_vlan(skb->protocol) &&
-	    __vlan_get_protocol(skb, skb->protocol, &depth) != 0) {
-		if (pskb_may_pull(skb, depth))
-			skb_set_network_header(skb, depth);
-	}
+	    vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0)
+		skb_set_network_header(skb, depth);
 
 	skb_probe_transport_header(skb);
 }