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
Fixes: 0ee288e69d03 ("bpf,perf: Fix perf_event_detach_bpf_prog error handling")
Reported-by: syzbot+2e0d2840414ce817aaac@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20241208142507.1207698-1-jolsa@xxxxxxxxxx
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a403b05a7091..1b8db5aee9d3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2250,6 +2250,9 @@ 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 +2261,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event)
bpf_prog_array_free_sleepable(old_array);
}
+put:
/*
* It could be that the bpf_prog is not sleepable (and will be freed
* via normal RCU), but is called from a point that supports sleepable
