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 ffff88003e149548 by task syz-executor6/3081

CPU: 3 PID: 3081 Comm: syz-executor6 Not tainted 4.13.0-rc5-next-20170816+ #4
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]
 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
 freezable_schedule include/linux/freezer.h:171 [inline]
 do_nanosleep+0x215/0x6f0 kernel/time/hrtimer.c:1473
 hrtimer_nanosleep+0x2b2/0x860 kernel/time/hrtimer.c:1527
 SYSC_nanosleep kernel/time/hrtimer.c:1559 [inline]
 SyS_nanosleep+0x175/0x1f0 kernel/time/hrtimer.c:1546
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4704d0
RSP: 002b:00007ffc9e141458 EFLAGS: 00000246 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 000000000000895e RCX: 00000000004704d0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffc9e141460
RBP: 00007ffc9e141470 R08: 0000000000000c09 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc9e141430
R13: 000000000000136a R14: 0000000000000019 R15: 0000000000008910

Allocated by task 4995:
 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 5004:
 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 ffff88003e149540
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff88003e149540, ffff88003e149560)
The buggy address belongs to the page:
page:ffffea0000f85240 count:1 mapcount:0 mapping:ffff88003e149000 index:0xffff88003e149fc1
flags: 0x100000000000100(slab)
raw: 0100000000000100 ffff88003e149000 ffff88003e149fc1 000000010000003d
raw: ffffea0000e5f760 ffffea0000f609e0 ffff88003e8001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88003e149400: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff88003e149480: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
>ffff88003e149500: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                                              ^
 ffff88003e149580: 00 00 00 fc fc fc fc fc 00 fc fc fc fc fc fc fc
 ffff88003e149600: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
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