syzbot

syz_tun: entered allmulticast mode
syz_tun: entered promiscuous mode
bridge0: port 4(syz_tun) entered blocking state
bridge0: port 4(syz_tun) entered forwarding state
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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:5215 [inline]
 netdev_start_xmit include/linux/netdevice.h:5224 [inline]
 xmit_one net/core/dev.c:3830 [inline]
 dev_hard_start_xmit+0x22c/0xa30 net/core/dev.c:3846
 sch_direct_xmit+0x3b2/0xcf0 net/sched/sch_generic.c:344
 __dev_xmit_skb net/core/dev.c:4102 [inline]
 __dev_queue_xmit+0x35e6/0x5e20 net/core/dev.c:4679
 dev_queue_xmit include/linux/netdevice.h:3355 [inline]
 br_dev_queue_push_xmit+0xa12/0xc20 net/bridge/br_forward.c:53
 NF_HOOK include/linux/netfilter.h:317 [inline]
 br_forward_finish+0xfe/0x330 net/bridge/br_forward.c:66
 NF_HOOK include/linux/netfilter.h:317 [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+0x2800/0x2a30 net/bridge/br_input.c:221
 nf_hook_bridge_pre net/bridge/br_input.c:305 [inline]
 br_handle_frame+0x1837/0x2190 net/bridge/br_input.c:434
 __netif_receive_skb_core+0x202e/0x70c0 net/core/dev.c:5863
 __netif_receive_skb_one_core net/core/dev.c:5975 [inline]
 __netif_receive_skb+0xcc/0xac0 net/core/dev.c:6090
 netif_receive_skb_internal net/core/dev.c:6176 [inline]
 netif_receive_skb+0x57/0x630 net/core/dev.c:6235
 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485
 tun_get_user+0x4ee0/0x6b40 drivers/net/tun.c:1938
 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1984
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0xb48/0x1580 fs/read_write.c:686
 ksys_write fs/read_write.c:738 [inline]
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746
 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+0xd9/0x210 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:4154 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_node_noprof+0x818/0xf00 mm/slub.c:4249
 kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:579
 pskb_expand_head+0x1fc/0x1610 net/core/skbuff.c:2241
 __skb_cow include/linux/skbuff.h:3777 [inline]
 skb_cow_head include/linux/skbuff.h:3811 [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:3869 [inline]
 validate_xmit_skb+0x5f6/0x1b90 net/core/dev.c:3939
 validate_xmit_skb_list+0xd4/0x320 net/core/dev.c:4000
 sch_direct_xmit+0xd4/0xcf0 net/sched/sch_generic.c:329
 __dev_xmit_skb net/core/dev.c:4102 [inline]
 __dev_queue_xmit+0x35e6/0x5e20 net/core/dev.c:4679
 dev_queue_xmit include/linux/netdevice.h:3355 [inline]
 br_dev_queue_push_xmit+0xa12/0xc20 net/bridge/br_forward.c:53
 NF_HOOK include/linux/netfilter.h:317 [inline]
 br_forward_finish+0xfe/0x330 net/bridge/br_forward.c:66
 NF_HOOK include/linux/netfilter.h:317 [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+0x2800/0x2a30 net/bridge/br_input.c:221
 nf_hook_bridge_pre net/bridge/br_input.c:305 [inline]
 br_handle_frame+0x1837/0x2190 net/bridge/br_input.c:434
 __netif_receive_skb_core+0x202e/0x70c0 net/core/dev.c:5863
 __netif_receive_skb_one_core net/core/dev.c:5975 [inline]
 __netif_receive_skb+0xcc/0xac0 net/core/dev.c:6090
 netif_receive_skb_internal net/core/dev.c:6176 [inline]
 netif_receive_skb+0x57/0x630 net/core/dev.c:6235
 tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485
 tun_get_user+0x4ee0/0x6b40 drivers/net/tun.c:1938
 tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1984
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0xb48/0x1580 fs/read_write.c:686
 ksys_write fs/read_write.c:738 [inline]
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746
 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+0xd9/0x210 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5839 Comm: syz-executor263 Not tainted 6.16.0-rc5-syzkaller-00276-g5d5d62298b8b #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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