==================================================================
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+0x7f8/0xa30 net/core/dev.c:4146
Read of size 2 at addr ffff88819bd546f4 by task syz.0.2887/17802

CPU: 1 UID: 0 PID: 17802 Comm: syz.0.2887 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 __tcp_hdrlen include/linux/tcp.h:31 [inline]
 qdisc_pkt_len_segs_init+0x7f8/0xa30 net/core/dev.c:4146
 __dev_queue_xmit+0x29a/0x3920 net/core/dev.c:4788
 dev_queue_xmit include/linux/netdevice.h:3401 [inline]
 hsr_xmit net/hsr/hsr_forward.c:440 [inline]
 hsr_forward_do net/hsr/hsr_forward.c:581 [inline]
 hsr_forward_skb+0x167e/0x2a80 net/hsr/hsr_forward.c:743
 hsr_handle_frame+0x6b8/0xa50 net/hsr/hsr_slave.c:81
 __netif_receive_skb_core+0x98f/0x31a0 net/core/dev.c:6101
 __netif_receive_skb_list_core+0x24d/0x810 net/core/dev.c:6289
 __netif_receive_skb_list net/core/dev.c:6356 [inline]
 netif_receive_skb_list_internal+0x995/0xcf0 net/core/dev.c:6447
 gro_normal_list include/net/gro.h:523 [inline]
 gro_flush_normal include/net/gro.h:531 [inline]
 napi_complete_done+0x299/0x730 net/core/dev.c:6815
 gro_cell_poll+0x5a9/0x5d0 net/core/gro_cells.c:74
 __napi_poll+0xae/0x340 net/core/dev.c:7742
 napi_poll net/core/dev.c:7805 [inline]
 net_rx_action+0x627/0xf70 net/core/dev.c:7962
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 do_softirq+0x76/0xd0 kernel/softirq.c:523
 </IRQ>
 <TASK>
 __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 tun_rx_batched+0x617/0x790 drivers/net/tun.c:-1
 tun_get_user+0x2aeb/0x3ed0 drivers/net/tun.c:1953
 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61d/0xb90 fs/read_write.c:688
 ksys_write+0x150/0x270 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f53dbf9c819
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:00007f53dcedb028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f53dc215fa0 RCX: 00007f53dbf9c819
RDX: 000000000000007a RSI: 0000200000000580 RDI: 0000000000000006
RBP: 00007f53dc032c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f53dc216038 R14: 00007f53dc215fa0 R15: 00007ffdc42e6fd8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x19bd54
flags: 0x57ff00000000000(node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000000 ffffea00066f5508 ffffea00066f5508 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:
 ffff88819bd54580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88819bd54600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88819bd54680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                             ^
 ffff88819bd54700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88819bd54780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================