KASAN: use-after-free Write in tlb_finish

Title	Repro	Cause bisect	Fix bisect	Count	Last	Reported
WARNING in __mmdrop kernel	syz	done		14	1730d	1740d
Title	Replies (including bot)	Last reply
KASAN: use-after-free Write in tlb_finish_mmu	1 (3)	2019/07/24 07:07
Reminder: 3 open syzbot bugs in vhost subsystem	3 (4)	2019/07/24 03:13
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BUG: KASAN: use-after-free in atomic_dec /./include/asm-generic/atomic-instrumented.h:329 [inline]
BUG: KASAN: use-after-free in dec_tlb_flush_pending /./include/linux/mm_types.h:598 [inline]
BUG: KASAN: use-after-free in tlb_finish_mmu+0x136/0x3b0 /mm/mmu_gather.c:279
Write of size 4 at addr ffff8880912433f4 by task syz-executor.0/9266

CPU: 1 PID: 9266 Comm: syz-executor.0 Not tainted 5.2.0+ #61
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack /lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 /lib/dump_stack.c:113
 print_address_description.cold+0xd4/0x306 /mm/kasan/report.c:351
 __kasan_report.cold+0x1b/0x36 /mm/kasan/report.c:482
 kasan_report+0x12/0x17 /mm/kasan/common.c:612
 check_memory_region_inline /mm/kasan/generic.c:185 [inline]
 check_memory_region+0x134/0x1a0 /mm/kasan/generic.c:192
 __kasan_check_write+0x14/0x20 /mm/kasan/common.c:98
 atomic_dec /./include/asm-generic/atomic-instrumented.h:329 [inline]
 dec_tlb_flush_pending /./include/linux/mm_types.h:598 [inline]
 tlb_finish_mmu+0x136/0x3b0 /mm/mmu_gather.c:279
 exit_mmap+0x2da/0x530 /mm/mmap.c:3147
 __mmput /kernel/fork.c:1064 [inline]
 mmput+0x179/0x4d0 /kernel/fork.c:1085
 exit_mm /kernel/exit.c:547 [inline]
 do_exit+0x84e/0x2ea0 /kernel/exit.c:864
 do_group_exit+0x135/0x360 /kernel/exit.c:981
 get_signal+0x47c/0x2500 /kernel/signal.c:2728
 do_signal+0x87/0x1670 /arch/x86/kernel/signal.c:815
 exit_to_usermode_loop+0x286/0x380 /arch/x86/entry/common.c:159
 prepare_exit_to_usermode /arch/x86/entry/common.c:194 [inline]
 syscall_return_slowpath /arch/x86/entry/common.c:274 [inline]
 do_syscall_32_irqs_on /arch/x86/entry/common.c:347 [inline]
 do_fast_syscall_32+0xb87/0xdb3 /arch/x86/entry/common.c:403
 entry_SYSENTER_compat+0x70/0x7f /arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f139c9
Code: d3 83 c4 10 5b 5e 5d c3 ba 80 96 98 00 eb a9 8b 04 24 c3 8b 34 24 c3 8b 3c 24 c3 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f7eee0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 000000004028af11
RDX: 00000000200023c0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9107:
 save_stack+0x23/0x90 /mm/kasan/common.c:69
 set_track /mm/kasan/common.c:77 [inline]
 __kasan_kmalloc /mm/kasan/common.c:487 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 /mm/kasan/common.c:460
 kasan_slab_alloc+0xf/0x20 /mm/kasan/common.c:495
 slab_post_alloc_hook /mm/slab.h:520 [inline]
 slab_alloc /mm/slab.c:3319 [inline]
 kmem_cache_alloc+0x121/0x710 /mm/slab.c:3483
 dup_mm+0x8a/0x1430 /kernel/fork.c:1337
 copy_mm /kernel/fork.c:1402 [inline]
 copy_process+0x28b7/0x6b00 /kernel/fork.c:2017
 _do_fork+0x146/0xfa0 /kernel/fork.c:2369
 __do_compat_sys_x86_clone /arch/x86/ia32/sys_ia32.c:253 [inline]
 __se_compat_sys_x86_clone /arch/x86/ia32/sys_ia32.c:236 [inline]
 __ia32_compat_sys_x86_clone+0x188/0x260 /arch/x86/ia32/sys_ia32.c:236
 do_syscall_32_irqs_on /arch/x86/entry/common.c:332 [inline]
 do_fast_syscall_32+0x27b/0xdb3 /arch/x86/entry/common.c:403
 entry_SYSENTER_compat+0x70/0x7f /arch/x86/entry/entry_64_compat.S:139

Freed by task 9107:
 save_stack+0x23/0x90 /mm/kasan/common.c:69
 set_track /mm/kasan/common.c:77 [inline]
 __kasan_slab_free+0x102/0x150 /mm/kasan/common.c:449
 kasan_slab_free+0xe/0x10 /mm/kasan/common.c:457
 __cache_free /mm/slab.c:3425 [inline]
 kmem_cache_free+0x86/0x320 /mm/slab.c:3693
 __mmdrop+0x238/0x320 /kernel/fork.c:683
 mmdrop /./include/linux/sched/mm.h:49 [inline]
 finish_task_switch+0x457/0x720 /kernel/sched/core.c:3123
 context_switch /kernel/sched/core.c:3257 [inline]
 __schedule+0x75d/0x1580 /kernel/sched/core.c:3880
 schedule+0xa8/0x270 /kernel/sched/core.c:3944
 freezable_schedule /./include/linux/freezer.h:172 [inline]
 do_nanosleep+0x201/0x6a0 /kernel/time/hrtimer.c:1679
 hrtimer_nanosleep+0x2a6/0x570 /kernel/time/hrtimer.c:1733
 __do_sys_nanosleep_time32 /kernel/time/hrtimer.c:1787 [inline]
 __se_sys_nanosleep_time32 /kernel/time/hrtimer.c:1774 [inline]
 __ia32_sys_nanosleep_time32+0x1ad/0x230 /kernel/time/hrtimer.c:1774
 do_syscall_32_irqs_on /arch/x86/entry/common.c:332 [inline]
 do_fast_syscall_32+0x27b/0xdb3 /arch/x86/entry/common.c:403
 entry_SYSENTER_compat+0x70/0x7f /arch/x86/entry/entry_64_compat.S:139

The buggy address belongs to the object at ffff888091242e80
 which belongs to the cache mm_struct(17:syz0) of size 1496
The buggy address is located 1396 bytes inside of
 1496-byte region [ffff888091242e80, ffff888091243458)
The buggy address belongs to the page:
page:ffffea0002449080 refcount:1 mapcount:0 mapping:ffff88809b48b700 index:0x0 compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea00021bb308 ffff8880a1533a48 ffff88809b48b700
raw: 0000000000000000 ffff888091242180 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888091243280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888091243300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888091243380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                             ^
 ffff888091243400: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
 ffff888091243480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
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