Date:   Tue, 19 Mar 2019 23:56:22 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: KASAN 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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