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BUG: KASAN: use-after-free in free_ldt_struct.part.2+0x10a/0x150 arch/x86/kernel/ldt.c:116
Read of size 4 at addr ffff88006d8a06c8 by task syz-executor2/9217
sctp: [Deprecated]: syz-executor5 (pid 9223) Use of struct sctp_assoc_value in delayed_ack socket option.
Use struct sctp_sack_info instead

CPU: 2 PID: 9217 Comm: syz-executor2 Not tainted 4.13.0-rc5-next-20170817+ #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x24e/0x340 mm/kasan/report.c:409
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 free_ldt_struct.part.2+0x10a/0x150 arch/x86/kernel/ldt.c:116
 free_ldt_struct arch/x86/kernel/ldt.c:173 [inline]
 destroy_context_ldt+0x60/0x80 arch/x86/kernel/ldt.c:171
 destroy_context arch/x86/include/asm/mmu_context.h:157 [inline]
 __mmdrop+0xe9/0x530 kernel/fork.c:890
 mmdrop include/linux/sched/mm.h:42 [inline]
 finish_task_switch+0x456/0x740 kernel/sched/core.c:2658
 context_switch kernel/sched/core.c:2789 [inline]
 __schedule+0x8f0/0x2070 kernel/sched/core.c:3362
 schedule+0x108/0x440 kernel/sched/core.c:3421
 schedule_timeout+0x1ce/0x250 kernel/time/timer.c:1688
 do_wait_for_common kernel/sched/completion.c:83 [inline]
 __wait_for_common kernel/sched/completion.c:104 [inline]
 wait_for_common kernel/sched/completion.c:115 [inline]
 wait_for_completion_killable+0x3e7/0x820 kernel/sched/completion.c:241
 call_usermodehelper_exec+0x372/0x540 kernel/umh.c:444
 call_modprobe kernel/kmod.c:99 [inline]
 __request_module+0x3ff/0xc00 kernel/kmod.c:171
 __sock_create+0x5f9/0x850 net/socket.c:1243
 sock_create net/socket.c:1302 [inline]
 SYSC_socketpair net/socket.c:1374 [inline]
 SyS_socketpair+0x115/0x640 net/socket.c:1353
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x446739
RSP: 002b:00007fa00cf14c08 EFLAGS: 00000296 ORIG_RAX: 0000000000000035
RAX: ffffffffffffffda RBX: 0000000000000013 RCX: 0000000000446739
RDX: 0000000000008001 RSI: 0000000000000005 RDI: 0000000000000013
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020000ff8 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fa00cf159c0 R15: 00007fa00cf15700

Allocated by task 9172:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3627
 kmalloc include/linux/slab.h:493 [inline]
 alloc_ldt_struct+0x52/0x140 arch/x86/kernel/ldt.c:67
 write_ldt+0x3ea/0xab0 arch/x86/kernel/ldt.c:277
 sys_modify_ldt+0x1ef/0x240 arch/x86/kernel/ldt.c:307
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 9172:
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xca/0x250 mm/slab.c:3820
 free_ldt_struct.part.2+0xdd/0x150 arch/x86/kernel/ldt.c:121
 free_ldt_struct arch/x86/kernel/ldt.c:173 [inline]
 destroy_context_ldt+0x60/0x80 arch/x86/kernel/ldt.c:171
 destroy_context arch/x86/include/asm/mmu_context.h:157 [inline]
 __mmdrop+0xe9/0x530 kernel/fork.c:890
 mmdrop include/linux/sched/mm.h:42 [inline]
 __mmput kernel/fork.c:917 [inline]
 mmput+0x541/0x6e0 kernel/fork.c:928
 copy_process.part.36+0x22e1/0x4af0 kernel/fork.c:1932
 copy_process kernel/fork.c:1547 [inline]
 _do_fork+0x1ef/0xfb0 kernel/fork.c:2026
 SYSC_clone kernel/fork.c:2136 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2130
 do_syscall_64+0x26c/0x8c0 arch/x86/entry/common.c:287
 return_from_SYSCALL_64+0x0/0x7a

The buggy address belongs to the object at ffff88006d8a06c0
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff88006d8a06c0, ffff88006d8a06e0)
The buggy address belongs to the page:
page:ffffea0001b62800 count:1 mapcount:0 mapping:ffff88006d8a0000 index:0xffff88006d8a0fc1
flags: 0x500000000000100(slab)
raw: 0500000000000100 ffff88006d8a0000 ffff88006d8a0fc1 0000000100000015
raw: ffffea0001b3dd60 ffffea0001b32660 ffff88003e8001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88006d8a0580: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88006d8a0600: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff88006d8a0680: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                                              ^
 ffff88006d8a0700: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88006d8a0780: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
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