If a instance has an event trigger enabled when it is freed, it could cause
an access of free memory. Here's the case that crashes:
# cd /sys/kernel/tracing
# mkdir instances/foo
# echo snapshot > instances/foo/events/initcall/initcall_start/trigger
# rmdir instances/foo
Would produce:
general protection fault: 0000 [#1] PREEMPT SMP PTI
Modules linked in: tun bridge ...
CPU: 5 PID: 6203 Comm: rmdir Tainted: G W 4.17.0-rc4-test+ #933
Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
RIP: 0010:clear_event_triggers+0x3b/0x70
RSP: 0018:ffffc90003783de0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 6b6b6b6b6b6b6b2b RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800c7130ba0
RBP: ffffc90003783e00 R08: ffff8801131993f8 R09: 0000000100230016
R10: ffffc90003783d80 R11: 0000000000000000 R12: ffff8800c7130ba0
R13: ffff8800c7130bd8 R14: ffff8800cc093768 R15: 00000000ffffff9c
FS: 00007f6f4aa86700(0000) GS:ffff88011eb40000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6f4a5aed60 CR3: 00000000cd552001 CR4: 00000000001606e0
Call Trace:
event_trace_del_tracer+0x2a/0xc5
instance_rmdir+0x15c/0x200
tracefs_syscall_rmdir+0x52/0x90
vfs_rmdir+0xdb/0x160
do_rmdir+0x16d/0x1c0
__x64_sys_rmdir+0x17/0x20
do_syscall_64+0x55/0x1a0
entry_SYSCALL_64_after_hwframe+0x49/0xbe
This was due to the call the clears out the triggers when an instance is
being deleted not removing the trigger from the link list.
Cc: stable@vger.kernel.org
Fixes: 85f2b08268 ("tracing: Add basic event trigger framework")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
86b389ff22