syz_tun: entered allmulticast mode
syz_tun: entered promiscuous mode
bridge0: port 3(syz_tun) entered blocking state
bridge0: port 3(syz_tun) entered forwarding state
=====================================================
BUG: KMSAN: uninit-value in ip6gre_xmit_ipv6 net/ipv6/ip6_gre.c:863 [inline]
BUG: KMSAN: uninit-value in ip6gre_tunnel_xmit+0xfee/0x1cf0 net/ipv6/ip6_gre.c:926
 ip6gre_xmit_ipv6 net/ipv6/ip6_gre.c:863 [inline]
 ip6gre_tunnel_xmit+0xfee/0x1cf0 net/ipv6/ip6_gre.c:926
 __netdev_start_xmit include/linux/netdevice.h:5203 [inline]
 netdev_start_xmit include/linux/netdevice.h:5212 [inline]
 xmit_one net/core/dev.c:3776 [inline]
 dev_hard_start_xmit+0x299/0xa30 net/core/dev.c:3792
 sch_direct_xmit+0x3b2/0xcf0 net/sched/sch_generic.c:343
 __dev_xmit_skb net/core/dev.c:4018 [inline]
 __dev_queue_xmit+0x35e6/0x5e20 net/core/dev.c:4595
 dev_queue_xmit include/linux/netdevice.h:3350 [inline]
 br_dev_queue_push_xmit+0xa12/0xc20 net/bridge/br_forward.c:53
 NF_HOOK include/linux/netfilter.h:314 [inline]
 br_forward_finish+0xfe/0x330 net/bridge/br_forward.c:66
 NF_HOOK include/linux/netfilter.h:314 [inline]
 __br_forward+0x8cc/0xb30 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver+0x3e8/0x590 net/bridge/br_forward.c:190
 br_flood+0x45b/0xb70 net/bridge/br_forward.c:237
 br_handle_frame_finish+0x26eb/0x2910 net/bridge/br_input.c:220
 nf_hook_bridge_pre net/bridge/br_input.c:304 [inline]
 br_handle_frame+0x1837/0x2190 net/bridge/br_input.c:433
 __netif_receive_skb_core+0x202b/0x70c0 net/core/dev.c:5773
 __netif_receive_skb_one_core net/core/dev.c:5885 [inline]
 __netif_receive_skb+0xcc/0xac0 net/core/dev.c:6000
 netif_receive_skb_internal net/core/dev.c:6086 [inline]
 netif_receive_skb+0x57/0x630 net/core/dev.c:6145
 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485
 tun_get_user+0x52a7/0x6a80 drivers/net/tun.c:1938
 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1984
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0xb31/0x1560 fs/read_write.c:684
 ksys_write fs/read_write.c:736 [inline]
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:744
 x64_sys_call+0x38c3/0x3db0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x1b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4167 [inline]
 slab_alloc_node mm/slub.c:4210 [inline]
 kmem_cache_alloc_node_noprof+0x818/0xf00 mm/slub.c:4262
 kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:577
 pskb_expand_head+0x207/0x1c90 net/core/skbuff.c:2247
 __skb_cow include/linux/skbuff.h:3772 [inline]
 skb_cow_head include/linux/skbuff.h:3806 [inline]
 __vlan_insert_inner_tag include/linux/if_vlan.h:355 [inline]
 vlan_insert_inner_tag include/linux/if_vlan.h:428 [inline]
 vlan_insert_tag include/linux/if_vlan.h:455 [inline]
 vlan_insert_tag_set_proto include/linux/if_vlan.h:476 [inline]
 __vlan_hwaccel_push_inside include/linux/if_vlan.h:516 [inline]
 validate_xmit_vlan net/core/dev.c:3815 [inline]
 validate_xmit_skb+0x1015/0x18d0 net/core/dev.c:3855
 validate_xmit_skb_list+0xd4/0x320 net/core/dev.c:3916
 sch_direct_xmit+0xd4/0xcf0 net/sched/sch_generic.c:328
 __dev_xmit_skb net/core/dev.c:4018 [inline]
 __dev_queue_xmit+0x35e6/0x5e20 net/core/dev.c:4595
 dev_queue_xmit include/linux/netdevice.h:3350 [inline]
 br_dev_queue_push_xmit+0xa12/0xc20 net/bridge/br_forward.c:53
 NF_HOOK include/linux/netfilter.h:314 [inline]
 br_forward_finish+0xfe/0x330 net/bridge/br_forward.c:66
 NF_HOOK include/linux/netfilter.h:314 [inline]
 __br_forward+0x8cc/0xb30 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver+0x3e8/0x590 net/bridge/br_forward.c:190
 br_flood+0x45b/0xb70 net/bridge/br_forward.c:237
 br_handle_frame_finish+0x26eb/0x2910 net/bridge/br_input.c:220
 nf_hook_bridge_pre net/bridge/br_input.c:304 [inline]
 br_handle_frame+0x1837/0x2190 net/bridge/br_input.c:433
 __netif_receive_skb_core+0x202b/0x70c0 net/core/dev.c:5773
 __netif_receive_skb_one_core net/core/dev.c:5885 [inline]
 __netif_receive_skb+0xcc/0xac0 net/core/dev.c:6000
 netif_receive_skb_internal net/core/dev.c:6086 [inline]
 netif_receive_skb+0x57/0x630 net/core/dev.c:6145
 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485
 tun_get_user+0x52a7/0x6a80 drivers/net/tun.c:1938
 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1984
 new_sync_write fs/read_write.c:591 [inline]
 vfs_write+0xb31/0x1560 fs/read_write.c:684
 ksys_write fs/read_write.c:736 [inline]
 __do_sys_write fs/read_write.c:747 [inline]
 __se_sys_write fs/read_write.c:744 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:744
 x64_sys_call+0x38c3/0x3db0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0x1b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 0 UID: 0 PID: 10991 Comm: syz.6.1208 Not tainted 6.15.0-rc3-syzkaller-00094-g02ddfb981de8 #0 PREEMPT(undef) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
=====================================================