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BUG: KASAN: use-after-free in __tcp_hdrlen include/linux/tcp.h:31 [inline]
BUG: KASAN: use-after-free in qdisc_pkt_len_segs_init+0xa51/0xb30 net/core/dev.c:4140
Read of size 2 at addr ffff88812ae91734 by task syz.0.1087/9735

CPU: 0 UID: 0 PID: 9735 Comm: syz.0.1087 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 __tcp_hdrlen include/linux/tcp.h:31 [inline]
 qdisc_pkt_len_segs_init+0xa51/0xb30 net/core/dev.c:4140
 __dev_queue_xmit+0x270/0x4950 net/core/dev.c:4782
 dev_queue_xmit include/linux/netdevice.h:3421 [inline]
 hsr_xmit net/hsr/hsr_forward.c:440 [inline]
 hsr_forward_do net/hsr/hsr_forward.c:581 [inline]
 hsr_forward_skb+0xdcf/0x28a0 net/hsr/hsr_forward.c:743
 hsr_handle_frame+0x82f/0xac0 net/hsr/hsr_slave.c:81
 __netif_receive_skb_core.constprop.0+0x6c5/0x3530 net/core/dev.c:6096
 __netif_receive_skb_list_core+0x353/0x940 net/core/dev.c:6284
 __netif_receive_skb_list net/core/dev.c:6351 [inline]
 netif_receive_skb_list_internal+0x722/0xd40 net/core/dev.c:6442
 gro_normal_list include/net/gro.h:523 [inline]
 gro_normal_list include/net/gro.h:519 [inline]
 gro_flush_normal include/net/gro.h:531 [inline]
 napi_complete_done+0x221/0x940 net/core/dev.c:6810
 gro_cell_poll+0x46e/0x690 net/core/gro_cells.c:74
 __napi_poll.constprop.0+0xaf/0x450 net/core/dev.c:7737
 napi_poll net/core/dev.c:7800 [inline]
 net_rx_action+0xa40/0xf20 net/core/dev.c:7957
 handle_softirqs+0x1ea/0xa00 kernel/softirq.c:622
 do_softirq kernel/softirq.c:523 [inline]
 do_softirq+0xac/0xe0 kernel/softirq.c:510
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xf8/0x120 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 tun_rx_batched.isra.0+0x407/0x750 drivers/net/tun.c:1512
 tun_get_user+0x1e31/0x3c20 drivers/net/tun.c:1955
 tun_chr_write_iter+0xdc/0x200 drivers/net/tun.c:2001
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f727bb9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f727c9e2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f727be15fa0 RCX: 00007f727bb9c819
RDX: 000000000000007a RSI: 0000200000000400 RDI: 000000000000000b
RBP: 00007f727bc32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f727be16038 R14: 00007f727be15fa0 R15: 00007ffd45d5f7d8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12ae91
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000000 ffffea0004aba448 ffffea0004aba448 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
 ffff88812ae91600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812ae91680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812ae91700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                     ^
 ffff88812ae91780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812ae91800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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