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BUG: KASAN: stack-out-of-bounds in __lookup_addr net/mptcp/pm_kernel.c:274 [inline]
BUG: KASAN: stack-out-of-bounds in mptcp_pm_nl_is_backup+0x187/0x2a0 net/mptcp/pm_kernel.c:917
Read of size 2 at addr ffffc90003617354 by task syz.3.603/8274

CPU: 0 UID: 0 PID: 8274 Comm: syz.3.603 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 __lookup_addr net/mptcp/pm_kernel.c:274 [inline]
 mptcp_pm_nl_is_backup+0x187/0x2a0 net/mptcp/pm_kernel.c:917
 mptcp_pm_is_backup+0x1a6/0x260 net/mptcp/pm.c:935
 subflow_chk_local_id+0x156/0x220 net/mptcp/subflow.c:643
 subflow_rebuild_header+0x16/0x50 net/mptcp/subflow.c:650
 tcp_connect+0x205/0x4f10 net/ipv4/tcp_output.c:4304
 tcp_v4_connect+0x11de/0x1a90 net/ipv4/tcp_ipv4.c:347
 mptcp_connect+0x56b/0x830 net/mptcp/protocol.c:3846
 __inet_stream_connect+0x2ae/0xe70 net/ipv4/af_inet.c:679
 inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:750
 __sys_connect_file net/socket.c:2102 [inline]
 __sys_connect+0x316/0x440 net/socket.c:2121
 __do_sys_connect net/socket.c:2127 [inline]
 __se_sys_connect net/socket.c:2124 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2124
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbffcd8f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbffdcc8038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fbffcfe5fa0 RCX: 00007fbffcd8f749
RDX: 0000000000000010 RSI: 0000200000000000 RDI: 000000000000000b
RBP: 00007fbffce13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbffcfe6038 R14: 00007fbffcfe5fa0 R15: 00007ffcdcc22528
 </TASK>

The buggy address belongs to a 8-page vmalloc region starting at 0xffffc90003610000 allocated at copy_process+0x54b/0x3c00 kernel/fork.c:2012
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888000000000 pfn:0x5b59c
memcg:ffff8880274d6482
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: ffff888000000000 0000000000000000 00000001ffffffff ffff8880274d6482
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x2dc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_ZERO|__GFP_NOWARN), pid 8270, tgid 8270 (syz.5.602), ts 148773539245, free_ts 148330325634
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1845
 prep_new_page mm/page_alloc.c:1853 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3879
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5178
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
 alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
 vm_area_alloc_pages mm/vmalloc.c:3647 [inline]
 __vmalloc_area_node mm/vmalloc.c:3724 [inline]
 __vmalloc_node_range_noprof+0x96c/0x12d0 mm/vmalloc.c:3897
 __vmalloc_node_noprof+0xc2/0x110 mm/vmalloc.c:3960
 alloc_thread_stack_node kernel/fork.c:311 [inline]
 dup_task_struct+0x3d4/0x830 kernel/fork.c:881
 copy_process+0x54b/0x3c00 kernel/fork.c:2012
 kernel_clone+0x21e/0x840 kernel/fork.c:2609
 __do_sys_clone3 kernel/fork.c:2911 [inline]
 __se_sys_clone3+0x256/0x2d0 kernel/fork.c:2890
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 15 tgid 15 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2901
 __tlb_remove_table_free mm/mmu_gather.c:227 [inline]
 tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
 rcu_do_batch kernel/rcu/tree.c:2605 [inline]
 rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
 handle_softirqs+0x286/0x870 kernel/softirq.c:622
 run_ksoftirqd+0x9b/0x100 kernel/softirq.c:1063
 smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffffc90003617200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90003617280: 00 00 00 00 f1 f1 f1 f1 00 01 f2 f2 00 01 f2 f2
>ffffc90003617300: 00 f2 f2 f2 00 f2 f2 f2 00 00 f3 f3 00 00 00 00
                                                 ^
 ffffc90003617380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffffc90003617400: f1 f1 f1 f1 00 00 00 00 00 00 00 00 00 00 00 00
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