KASAN: use-after-free Read in task_is_descendant

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    270b77a0f30e Merge tag 'drm-fixes-2018-10-20-1' of git://a..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=116f4ad9400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b3f55cb3dfcc6c33
dashboard link: https://syzkaller.appspot.com/bug?extid=a9ac39bf55329e206219
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a9ac39bf55329e206219@xxxxxxxxxxxxxxxxxxxxxxxxx

binder: 12719:12721 got transaction to context manager from process owning  
it
binder: BINDER_SET_CONTEXT_MGR already set
binder: 12719:12724 ioctl 40046207 0 returned -16
binder: 12719:12721 BC_ACQUIRE_DONE u0000000000000000 no match
==================================================================
BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:188  
[inline]
BUG: KASAN: use-after-free in task_is_descendant.part.2+0x610/0x670  
security/yama/yama_lsm.c:295
Read of size 8 at addr ffff8801c4666b20 by task syz-executor3/12722

CPU: 1 PID: 12722 Comm: syz-executor3 Not tainted 4.19.0-rc8+ #70
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+0x1c4/0x2b4 lib/dump_stack.c:113
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 __read_once_size include/linux/compiler.h:188 [inline]
 task_is_descendant.part.2+0x610/0x670 security/yama/yama_lsm.c:295
 task_is_descendant security/yama/yama_lsm.c:282 [inline]
 yama_ptrace_access_check+0x215/0x10fc security/yama/yama_lsm.c:371
 security_ptrace_access_check+0x54/0xb0 security/security.c:260
 __ptrace_may_access+0x564/0x950 kernel/ptrace.c:331
 ptrace_attach+0x1fa/0x640 kernel/ptrace.c:379
 __do_sys_ptrace kernel/ptrace.c:1130 [inline]
 __se_sys_ptrace kernel/ptrace.c:1110 [inline]
 __x64_sys_ptrace+0x229/0x260 kernel/ptrace.c:1110
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7df12c4c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000065
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000000000265 RDI: 0000000000000010
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7df12c56d4
R13: 00000000004c30c5 R14: 00000000004d4ab8 R15: 00000000ffffffff

Allocated by task 8920:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc_node+0x144/0x730 mm/slab.c:3644
 alloc_task_struct_node kernel/fork.c:157 [inline]
 dup_task_struct kernel/fork.c:802 [inline]
 copy_process+0x1ff4/0x8780 kernel/fork.c:1707
 _do_fork+0x1cb/0x11d0 kernel/fork.c:2166
 __do_sys_clone kernel/fork.c:2273 [inline]
 __se_sys_clone kernel/fork.c:2267 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2267
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 18:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kmem_cache_free+0x83/0x290 mm/slab.c:3756
 free_task_struct kernel/fork.c:162 [inline]
 free_task+0x16e/0x1f0 kernel/fork.c:416
 __put_task_struct+0x2e6/0x620 kernel/fork.c:689
 put_task_struct include/linux/sched/task.h:96 [inline]
 delayed_put_task_struct+0x2ff/0x4c0 kernel/exit.c:181
 __rcu_reclaim kernel/rcu/rcu.h:236 [inline]
 rcu_do_batch kernel/rcu/tree.c:2576 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2880 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2847 [inline]
 rcu_process_callbacks+0xf23/0x2670 kernel/rcu/tree.c:2864
 __do_softirq+0x30b/0xad8 kernel/softirq.c:292

The buggy address belongs to the object at ffff8801c4666640
 which belongs to the cache task_struct(65:syz3) of size 6080
The buggy address is located 1248 bytes inside of
 6080-byte region [ffff8801c4666640, ffff8801c4667e00)
The buggy address belongs to the page:
page:ffffea0007119980 count:1 mapcount:0 mapping:ffff8801c2336800 index:0x0  
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea00070a0008 ffffea0006080688 ffff8801c2336800
raw: 0000000000000000 ffff8801c4666640 0000000100000001 ffff8801bdb40c00
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801bdb40c00

Memory state around the buggy address:
 ffff8801c4666a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c4666a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801c4666b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff8801c4666b80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801c4666c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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