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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 ffff88003dbae9c8 by task syz-executor0/13675

CPU: 0 PID: 13675 Comm: syz-executor0 Not tainted 4.13.0-rc4-next-20170811 #2
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:889
 mmdrop include/linux/sched/mm.h:42 [inline]
 __mmput kernel/fork.c:916 [inline]
 mmput+0x541/0x6e0 kernel/fork.c:927
 exit_mm kernel/exit.c:544 [inline]
 do_exit+0x9a1/0x1b30 kernel/exit.c:852
 do_group_exit+0x149/0x400 kernel/exit.c:968
 get_signal+0x7e8/0x17e0 kernel/signal.c:2330
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x224/0x300 arch/x86/entry/common.c:158
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:266 [inline]
 do_syscall_64+0x65c/0x8c0 arch/x86/entry/common.c:292
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x446739
RSP: 002b:00007f2119d30c08 EFLAGS: 00000286 ORIG_RAX: 0000000000000038
RAX: fffffffffffffdff RBX: 0000000000800000 RCX: 0000000000446739
RDX: 0000000020507ffc RSI: 00000000208a8f43 RDI: 0000000000800000
RBP: 0000000000708000 R08: 0000000020a8a000 R09: 0000000000000000
R10: 0000000020117ffc R11: 0000000000000286 R12: 00000000ffffffff
R13: 00000000000003b0 R14: 00000000006e2470 R15: 00000000208a8f43

Allocated by task 13675:
 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 13675:
 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:889
 mmdrop include/linux/sched/mm.h:42 [inline]
 __mmput kernel/fork.c:916 [inline]
 mmput+0x541/0x6e0 kernel/fork.c:927
 copy_process.part.36+0x22e1/0x4af0 kernel/fork.c:1931
 copy_process kernel/fork.c:1546 [inline]
 _do_fork+0x1ef/0xfb0 kernel/fork.c:2025
 SYSC_clone kernel/fork.c:2135 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2129
 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 ffff88003dbae9c0
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff88003dbae9c0, ffff88003dbae9e0)
The buggy address belongs to the page:
page:ffffea0000f6eb80 count:1 mapcount:0 mapping:ffff88003dbae000 index:0xffff88003dbaefc1
flags: 0x100000000000100(slab)
raw: 0100000000000100 ffff88003dbae000 ffff88003dbaefc1 000000010000003d
raw: ffffea0000f4c720 ffffea0000f21ea0 ffff88003e8001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88003dbae880: 00 00 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88003dbae900: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff88003dbae980: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                                              ^
 ffff88003dbaea00: 00 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88003dbaea80: 07 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
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