bpf,perf: Fix invalid prog_array access in perf_event_detach_bpf_prog

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@syzkaller.appspotmail.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241208142507.1207698-1-jolsa@kernel.org

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a403b05a7091384fb08e8c47ed02fad79c1a4874..1b8db5aee9d38cb76f9e7e604fafca297ee24efa 100644 (file)
--- 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