Syzbot reported [1] crash that happens for following tracing scenario:
- create tracepoint perf event with attr.inherit=1, attach it to the
process and set bpf program to it
- attached process forks -> chid creates inherited event
the new child event shares the parent's bpf program and tp_event
(hence prog_array) which is global for tracepoint
- exit both process and its child -> release both events
- first perf_event_detach_bpf_prog call will release tp_event->prog_array
and second perf_event_detach_bpf_prog will crash, because
tp_event->prog_array is NULL
The fix makes sure the perf_event_detach_bpf_prog checks prog_array
is valid before it tries to remove the bpf program from it.
[1] https://lore.kernel.org/bpf/Z1MR6dCIKajNS6nU@krava/T/#m91dbf0688221ec7a7fc95e896a7ef9ff93b0b8ad
Reported-by: syzbot+2e0d2840414ce817aaac@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 0ee288e69d03 ("bpf,perf: Fix perf_event_detach_bpf_prog error handling")
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
kernel/trace/bpf_trace.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 949a3870946c..745cd72377d4 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2250,6 +2250,8 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
goto unlock;
old_array = bpf_event_rcu_dereference(event->tp_event->prog_array);
+ if (!old_array)
+ goto put;
ret = bpf_prog_array_copy(old_array, event->prog, NULL, 0, &new_array);
if (ret < 0) {
bpf_prog_array_delete_safe(old_array, event->prog);
@@ -2258,6 +2260,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
bpf_prog_array_free_sleepable(old_array);
}
+put:
bpf_prog_put(event->prog);
event->prog = NULL;
--
2.47.0
