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SubjectKASAN use after free
Hi Tom,

I ran the latest kernel (5.1-rc1) with full KASAN enabled, and ran the
ftrace tests, and hit the following:

==================================================================
BUG: KASAN: use-after-free in destroy_hist_field+0x30/0x70
Read of size 8 at addr ffff888086df2210 by task bash/1694

CPU: 6 PID: 1694 Comm: bash Not tainted 5.1.0-rc1-test+ #15
Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
Call Trace:
dump_stack+0x71/0xa0
? destroy_hist_field+0x30/0x70
print_address_description.cold.3+0x9/0x1fb
? destroy_hist_field+0x30/0x70
? destroy_hist_field+0x30/0x70
kasan_report.cold.4+0x1a/0x33
? __kasan_slab_free+0x100/0x150
? destroy_hist_field+0x30/0x70
destroy_hist_field+0x30/0x70
track_data_destroy+0x55/0xe0
destroy_hist_data+0x1f0/0x350
hist_unreg_all+0x203/0x220
event_trigger_open+0xbb/0x130
do_dentry_open+0x296/0x700
? stacktrace_count_trigger+0x30/0x30
? generic_permission+0x56/0x200
? __x64_sys_fchdir+0xd0/0xd0
? inode_permission+0x55/0x200
? security_inode_permission+0x18/0x60
path_openat+0x633/0x22b0
? path_lookupat.isra.50+0x420/0x420
? __kasan_kmalloc.constprop.12+0xc1/0xd0
? kmem_cache_alloc+0xe5/0x260
? getname_flags+0x6c/0x2a0
? do_sys_open+0x149/0x2b0
? do_syscall_64+0x73/0x1b0
? entry_SYSCALL_64_after_hwframe+0x44/0xa9
? _raw_write_lock_bh+0xe0/0xe0
? __kernel_text_address+0xe/0x30
? unwind_get_return_address+0x2f/0x50
? __list_add_valid+0x2d/0x70
? deactivate_slab.isra.62+0x1f4/0x5a0
? getname_flags+0x6c/0x2a0
? set_track+0x76/0x120
do_filp_open+0x11a/0x1a0
? may_open_dev+0x50/0x50
? _raw_spin_lock+0x7a/0xd0
? _raw_write_lock_bh+0xe0/0xe0
? __alloc_fd+0x10f/0x200
do_sys_open+0x1db/0x2b0
? filp_open+0x50/0x50
do_syscall_64+0x73/0x1b0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fa7b24a4ca2
Code: 25 00 00 41 00 3d 00 00 41 00 74 4c 48 8d 05 85 7a 0d 00 8b 00 85 c0 75 6d 89 f2 b8 01 01 00 00 48 89 fe bf 9c ff ff ff 0f 05 <48> 3d 00 f0 ff ff 0f 87 a2 00 00 00 48 8b 4c 24 28 64 48 33 0c 25
RSP: 002b:00007fffbafb3af0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 000055d3648ade30 RCX: 00007fa7b24a4ca2
RDX: 0000000000000241 RSI: 000055d364a55240 RDI: 00000000ffffff9c
RBP: 00007fffbafb3bf0 R08: 0000000000000020 R09: 0000000000000002
R10: 00000000000001b6 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000003 R14: 0000000000000001 R15: 000055d364a55240

Allocated by task 1694:
__kasan_kmalloc.constprop.12+0xc1/0xd0
kmem_cache_alloc_trace+0x11a/0x280
create_hist_field+0x54/0x460
create_var_ref+0x2f/0xb0
event_hist_trigger_func+0x19cb/0x26a0
event_trigger_write+0x1a7/0x250
vfs_write+0xe1/0x240
ksys_write+0xa1/0x130
do_syscall_64+0x73/0x1b0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 1694:
__kasan_slab_free+0x111/0x150
kfree+0x8d/0x1c0
destroy_hist_data+0x13b/0x350
hist_unreg_all+0x203/0x220
event_trigger_open+0xbb/0x130
do_dentry_open+0x296/0x700
path_openat+0x633/0x22b0
do_filp_open+0x11a/0x1a0
do_sys_open+0x1db/0x2b0
do_syscall_64+0x73/0x1b0
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff888086df2208
which belongs to the cache kmalloc-192 of size 192
The buggy address is located 8 bytes inside of
192-byte region [ffff888086df2208, ffff888086df22c8)
The buggy address belongs to the page:
page:ffffea00021b7c00 count:1 mapcount:0 mapping:ffff8880d000cc40 index:0x0 compound_mapcount: 0
flags: 0xffff000010200(slab|head)
raw: 000ffff000010200 ffffea00021b7708 ffffea000312ee08 ffff8880d000cc40
raw: 0000000000000000 00000000001e001e 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888086df2100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888086df2180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888086df2200: fc fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888086df2280: fb fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc
ffff888086df2300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
Disabling lock debugging due to kernel taint

I can easily reproduce it with the following commands:

# cd /sys/kernel/debug/tracing
# echo 'hist:keys=pid:vals=hitcount:ts0=common_timestamp.usecs:sort=hitcount:size=2048:clock=global if comm=="ping"' > \
events/sched/sched_waking/trigger
# echo 'hist:keys=next_pid:vals=hitcount:wakeup_lat=common_timestamp.usecs-$ts0:sort=hitcount:size=2048:clock=global:onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) if next_comm=="ping"' > \
events/sched/sched_switch/trigger
# echo '!hist:keys=next_pid:vals=hitcount:wakeup_lat=common_timestamp.usecs-$ts0:sort=hitcount:size=2048:clock=global:onmax($wakeup_lat).save(next_comm,prev_pid,prev_prio,prev_comm) if next_comm=="ping"' > \
events/sched/sched_switch/trigger

And boom, KASAN complains.

I tried to debug it, but the hist code is rather complex, and I can't
figure out how the var_refs is associated to the fields. I figured I'd
pass it off to you.

-- Steve

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