net: bridge: fix vlan tunnel dst refcnt when egressing

In the Linux kernel, the following vulnerability has been resolved: net: bridge: fix vlan tunnel dst refcnt when egressing The egress tunnel code uses dst_clone() and directly sets the result which is wrong because the entry might have 0 refcnt or be already deleted, causing number of problems. It also triggers the WARN_ON() in dst_hold()[1] when a refcnt couldn't be taken. Fix it by using dst_hold_safe() and checking if a reference was actually taken before setting the dst. [1] dmesg WARN_ON log and following refcnt errors WARNING: CPU: 5 PID: 38 at include/net/dst.h:230 br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge] Modules linked in: 8021q garp mrp bridge stp llc bonding ipv6 virtio_net CPU: 5 PID: 38 Comm: ksoftirqd/5 Kdump: loaded Tainted: G W 5.13.0-rc3+ #360 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-1.fc33 04/01/2014 RIP: 0010:br_handle_egress_vlan_tunnel+0x10b/0x134 [bridge] Code: e8 85 bc 01 e1 45 84 f6 74 90 45 31 f6 85 db 48 c7 c7 a0 02 19 a0 41 0f 94 c6 31 c9 31 d2 44 89 f6 e8 64 bc 01 e1 85 db 75 02 <0f> 0b 31 c9 31 d2 44 89 f6 48 c7 c7 70 02 19 a0 e8 4b bc 01 e1 49 RSP: 0018:ffff8881003d39e8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa01902a0 RBP: ffff8881040c6700 R08: 0000000000000000 R09: 0000000000000001 R10: 2ce93d0054fe0d00 R11: 54fe0d00000e0000 R12: ffff888109515000 R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000401 FS: 0000000000000000(0000) GS:ffff88822bf40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f42ba70f030 CR3: 0000000109926000 CR4: 00000000000006e0 Call Trace: br_handle_vlan+0xbc/0xca [bridge] __br_forward+0x23/0x164 [bridge] deliver_clone+0x41/0x48 [bridge] br_handle_frame_finish+0x36f/0x3aa [bridge] ? skb_dst+0x2e/0x38 [bridge] ? br_handle_ingress_vlan_tunnel+0x3e/0x1c8 [bridge] ? br_handle_frame_finish+0x3aa/0x3aa [bridge] br_handle_frame+0x2c3/0x377 [bridge] ? __skb_pull+0x33/0x51 ? vlan_do_receive+0x4f/0x36a ? br_handle_frame_finish+0x3aa/0x3aa [bridge] __netif_receive_skb_core+0x539/0x7c6 ? __list_del_entry_valid+0x16e/0x1c2 __netif_receive_skb_list_core+0x6d/0xd6 netif_receive_skb_list_internal+0x1d9/0x1fa gro_normal_list+0x22/0x3e dev_gro_receive+0x55b/0x600 ? detach_buf_split+0x58/0x140 napi_gro_receive+0x94/0x12e virtnet_poll+0x15d/0x315 [virtio_net] __napi_poll+0x2c/0x1c9 net_rx_action+0xe6/0x1fb __do_softirq+0x115/0x2d8 run_ksoftirqd+0x18/0x20 smpboot_thread_fn+0x183/0x19c ? smpboot_unregister_percpu_thread+0x66/0x66 kthread+0x10a/0x10f ? kthread_mod_delayed_work+0xb6/0xb6 ret_from_fork+0x22/0x30 ---[ end trace 49f61b07f775fd2b ]--- dst_release: dst:00000000c02d677a refcnt:-1 dst_release underflow