When two hist triggers on different events are registered with the same
name=, the second one reuses the first as named_data. Both are added to
tr->hist_vars by save_hist_vars() during event_hist_trigger_parse(),
because save_hist_vars() is called before event_trigger_register() while
the named reuse is only detected later, in hist_register_trigger().
In the named-data branch hist_register_trigger() then frees the second
histogram's hist_data via destroy_hist_data(), but never removes its
tr->hist_vars list entry, leaving a dangling pointer and leaking the
trace_array reference it holds.
A later hist trigger that references a variable makes find_var_file()
walk tr->hist_vars and dereference the freed hist_data. The bug is
reproducible from userspace by writing three hist triggers to tracefs:
echo 'hist:keys=common_pid:x=common_pid:name=mh' > \
/sys/kernel/tracing/events/sched/sched_switch/trigger
echo 'hist:keys=common_pid:x=common_pid:name=mh' > \
/sys/kernel/tracing/events/sched/sched_process_fork/trigger
echo 'hist:keys=common_pid:vals=$x' > \
/sys/kernel/tracing/events/sched/sched_process_exit/trigger
The third write panics the kernel:
BUG: KASAN: slab-use-after-free in find_var_file.part.0+0x272/0x290
Read of size 8 at addr ffff888001f8a0e0 by task sh/1
CPU: 1 UID: 0 PID: 1 Comm: sh Tainted: G D N
Call Trace:
find_var_file.part.0
find_event_var
parse_atom
parse_expr
__create_val_field
event_hist_trigger_parse
trigger_process_regex
event_trigger_write
vfs_write
ksys_write
do_syscall_64
entry_SYSCALL_64_after_hwframe
Allocated by task 1:
event_hist_trigger_parse
Freed by task 1:
hist_register_trigger+0x618/0xa30
event_hist_trigger_parse
The buggy address belongs to freed 2048-byte region
Oops: general protection fault ... RIP: find_var_file.part.0
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
Fix by removing the hist_data from tr->hist_vars and releasing the
trace_array reference in the named-data branch of hist_register_trigger()
before freeing the hist_data.
Fixes: 6f86bdeab633 ("tracing: Fix bad hist from corrupting named_triggers
list")
Cc: [email protected]
Signed-off-by: Hui Su <[email protected]>
---
kernel/trace/trace_events_hist.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 58d28cd1afa3..6bf00710fd10 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -6641,8 +6641,10 @@ static int hist_register_trigger(char *glob,
tracing_set_filter_buffering(file->tr, true);
}
- if (named_data)
+ if (named_data) {
+ remove_hist_vars(hist_data);
destroy_hist_data(hist_data);
+ }
out:
return ret;
}
--
2.54.0
