BUG: KASAN: use-after-free in free_ldt_struct.part.2+0x10a/0x150 arch/x86/kernel/ldt.c:95
Read of size 4 at addr ffff8801c6205408 by task syz-executor0/4028

CPU: 0 PID: 4028 Comm: syz-executor0 Not tainted 4.13.0-rc6+ #45
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:95
 free_ldt_struct arch/x86/kernel/ldt.c:152 [inline]
 destroy_context_ldt+0x60/0x80 arch/x86/kernel/ldt.c:150
 destroy_context arch/x86/include/asm/mmu_context.h:149 [inline]
 __mmdrop+0xe9/0x530 kernel/fork.c:887
 mmdrop include/linux/sched/mm.h:42 [inline]
 __mmput kernel/fork.c:914 [inline]
 mmput+0x541/0x6e0 kernel/fork.c:925
 exit_mm kernel/exit.c:544 [inline]
 do_exit+0x989/0x1b10 kernel/exit.c:852
 do_group_exit+0x149/0x400 kernel/exit.c:969
 get_signal+0x7e8/0x17e0 kernel/signal.c:2334
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:808
 exit_to_usermode_loop+0x224/0x300 arch/x86/entry/common.c:157
 prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:263 [inline]
 do_syscall_64+0x5d4/0x800 arch/x86/entry/common.c:289
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x4512e9
RSP: 002b:00007f7063002c08 EFLAGS: 00000216 ORIG_RAX: 0000000000000038
RAX: fffffffffffffdff RBX: 00000000007180a8 RCX: 00000000004512e9
RDX: 0000000020507ffc RSI: 00000000208a8f43 RDI: 0000000000800000
RBP: 00000000000003b0 R08: 0000000020a8a000 R09: 0000000000000000
R10: 0000000020117ffc R11: 0000000000000216 R12: 00000000004b65e0
R13: 00000000ffffffff R14: 0000000000800000 R15: 00000000208a8f43

Allocated by task 4008:
 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+0x12f/0x740 mm/slab.c:3627
 kmalloc include/linux/slab.h:493 [inline]
 alloc_ldt_struct+0x52/0x140 arch/x86/kernel/ldt.c:46
 write_ldt+0x7b4/0xac0 arch/x86/kernel/ldt.c:256
 sys_modify_ldt+0x1ef/0x240 arch/x86/kernel/ldt.c:286
 entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 4028:
 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:100
 free_ldt_struct arch/x86/kernel/ldt.c:152 [inline]
 destroy_context_ldt+0x60/0x80 arch/x86/kernel/ldt.c:150
 destroy_context arch/x86/include/asm/mmu_context.h:149 [inline]
 __mmdrop+0xe9/0x530 kernel/fork.c:887
 mmdrop include/linux/sched/mm.h:42 [inline]
 __mmput kernel/fork.c:914 [inline]
 mmput+0x541/0x6e0 kernel/fork.c:925
 copy_process.part.34+0x2315/0x4bd0 kernel/fork.c:1933
 copy_process kernel/fork.c:1545 [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/0x800 arch/x86/entry/common.c:284
 return_from_SYSCALL_64+0x0/0x7a

The buggy address belongs to the object at ffff8801c6205400
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 8 bytes inside of
 32-byte region [ffff8801c6205400, ffff8801c6205420)
The buggy address belongs to the page:
page:ffffea0007188140 count:1 mapcount:0 mapping:ffff8801c6205000 index:0xffff8801c6205fc1
flags: 0x200000000000100(slab)
raw: 0200000000000100 ffff8801c6205000 ffff8801c6205fc1 000000010000003f
raw: ffffea0007187b60 ffffea0007185ee0 ffff8801dac001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c6205300: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801c6205380: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
>ffff8801c6205400: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
                      ^
 ffff8801c6205480: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
 ffff8801c6205500: 00 00 00 fc fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================