Re: KASAN: use-after-free Read in refcount_sub_and_test_checked (2)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    6d906f99 Merge tag 'arm64-fixes' of git://git.kernel.org/p..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=129b4003200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=856fc6d0fbbeede9
dashboard link: https://syzkaller.appspot.com/bug?extid=b0775615fa4c4479b691
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15df396b200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+b0775615fa4c4479b691@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in atomic_read  
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: use-after-free in refcount_sub_and_test_checked+0x87/0x200  
lib/refcount.c:182
Read of size 4 at addr ffff8880a8d5e060 by task syz-executor.0/31157

CPU: 0 PID: 31157 Comm: syz-executor.0 Not tainted 5.1.0-rc5+ #74
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+0x7c/0x20d mm/kasan/report.c:187
 kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
 check_memory_region_inline mm/kasan/generic.c:185 [inline]
 check_memory_region+0x123/0x190 mm/kasan/generic.c:191
 kasan_check_read+0x11/0x20 mm/kasan/common.c:102
 atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
 refcount_sub_and_test_checked+0x87/0x200 lib/refcount.c:182
 refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220
 put_task_struct include/linux/sched/task.h:97 [inline]
 _free_event+0x3d7/0x13b0 kernel/events/core.c:4460
 free_event+0x5f/0xd0 kernel/events/core.c:4481
 perf_event_release_kernel+0x5b2/0xbe0 kernel/events/core.c:4642
 perf_release+0x37/0x50 kernel/events/core.c:4656
 __fput+0x2e5/0x8d0 fs/file_table.c:278
 ____fput+0x16/0x20 fs/file_table.c:309
 task_work_run+0x14a/0x1c0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x273/0x2c0 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x52d/0x610 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4129e1
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 e4 1a 00 00 c3 48  
83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48  
89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffc793703e0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 00000000004129e1
RDX: 0000000000000000 RSI: 0000000000000081 RDI: 0000000000000003
RBP: 0000000000741220 R08: 0000000000741218 R09: 000000000002c9b0
R10: 00007ffc793704a0 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000001 R14: 0000000000000003 R15: 000000000073bfac

Allocated by task 31160:
 save_stack+0x45/0xd0 mm/kasan/common.c:75
 set_track mm/kasan/common.c:87 [inline]
 __kasan_kmalloc mm/kasan/common.c:497 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:470
 kasan_slab_alloc+0xf/0x20 mm/kasan/common.c:505
 slab_post_alloc_hook mm/slab.h:437 [inline]
 slab_alloc_node mm/slab.c:3337 [inline]
 kmem_cache_alloc_node+0x131/0x710 mm/slab.c:3647
 alloc_task_struct_node kernel/fork.c:157 [inline]
 dup_task_struct kernel/fork.c:844 [inline]
 copy_process.part.0+0x1d08/0x7980 kernel/fork.c:1752
 copy_process kernel/fork.c:1709 [inline]
 _do_fork+0x257/0xfd0 kernel/fork.c:2226
 __do_sys_clone kernel/fork.c:2333 [inline]
 __se_sys_clone kernel/fork.c:2327 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2327
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 31160:
 save_stack+0x45/0xd0 mm/kasan/common.c:75
 set_track mm/kasan/common.c:87 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:459
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:467
 __cache_free mm/slab.c:3500 [inline]
 kmem_cache_free+0x86/0x260 mm/slab.c:3766
 free_task_struct kernel/fork.c:162 [inline]
 free_task+0xdd/0x120 kernel/fork.c:457
 copy_process.part.0+0x1a3a/0x7980 kernel/fork.c:2158
 copy_process kernel/fork.c:1709 [inline]
 _do_fork+0x257/0xfd0 kernel/fork.c:2226
 __do_sys_clone kernel/fork.c:2333 [inline]
 __se_sys_clone kernel/fork.c:2327 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2327
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a8d5e040
 which belongs to the cache task_struct(44:syz0) of size 6080
The buggy address is located 32 bytes inside of
 6080-byte region [ffff8880a8d5e040, ffff8880a8d5f800)
The buggy address belongs to the page:
page:ffffea0002a35780 count:1 mapcount:0 mapping:ffff88808b2adcc0 index:0x0  
compound_mapcount: 0
flags: 0x1fffc0000010200(slab|head)
raw: 01fffc0000010200 ffffea0002301808 ffffea0002171f08 ffff88808b2adcc0
raw: 0000000000000000 ffff8880a8d5e040 0000000100000001 ffff888085710580
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff888085710580

Memory state around the buggy address:
 ffff8880a8d5df00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880a8d5df80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a8d5e000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                       ^
 ffff8880a8d5e080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880a8d5e100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================