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 ffff8801dadf5b48 by task syz-execprog/3039

CPU: 0 PID: 3039 Comm: syz-execprog Not tainted 4.13.0-rc5-next-20170816+ #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 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
 schedule_hrtimeout_range_clock+0x681/0x810 kernel/time/hrtimer.c:1696
 schedule_hrtimeout_range+0x2a/0x40 kernel/time/hrtimer.c:1753
 ep_poll+0xa2f/0x11a0 fs/eventpoll.c:1819
 SYSC_epoll_wait fs/eventpoll.c:2193 [inline]
 SyS_epoll_wait+0x167/0x1c0 fs/eventpoll.c:2158
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x457999
RSP: 002b:000000c420031850 EFLAGS: 00000246 ORIG_RAX: 00000000000000e8
RAX: ffffffffffffffda RBX: 00000000ffffffff RCX: 0000000000457999
RDX: 0000000000000080 RSI: 000000c420031890 RDI: 0000000000000004
RBP: 0000000000000086 R08: 0000000000000003 R09: 000000c420000900
R10: 00000000ffffffff R11: 0000000000000246 R12: 000000c4204477d0
R13: 0000000000699fb0 R14: 00000000004550b0 R15: 0000000000000000

Allocated by task 3576:
 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 3576:
 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 ffff8801dadf5b40
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff8801dadf5b40, ffff8801dadf5b60)
The buggy address belongs to the page:
page:ffffea00076b7d40 count:1 mapcount:0 mapping:ffff8801dadf5000 index:0xffff8801dadf5fc1
flags: 0x200000000000100(slab)
raw: 0200000000000100 ffff8801dadf5000 ffff8801dadf5fc1 0000000100000039
raw: ffffea0007610f60 ffff8801dac01238 ffff8801dac001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801dadf5a00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801dadf5a80: 00 03 fc fc fc fc fc fc 00 03 fc fc fc fc fc fc
>ffff8801dadf5b00: 00 03 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
                                              ^
 ffff8801dadf5b80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801dadf5c00: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================