On 4/9/18 9:18 AM, Yonghong Song wrote:
syzbot reported a possible deadlock in perf_event_detach_bpf_prog.
...
@@ -985,16 +986,31 @@ int perf_event_query_prog_array(struct perf_event *event,
void __user *info)
return -EINVAL;
if (copy_from_user(&query, uquery, sizeof(query)))
return -EFAULT;
- if (query.ids_len > BPF_TRACE_MAX_PROGS)
+
+ ids_len = query.ids_len;
+ if (ids_len > BPF_TRACE_MAX_PROGS)
return -E2BIG;
+ ids = kcalloc(ids_len, sizeof(u32), GFP_USER | __GFP_NOWARN);
+ if (!ids)
+ return -ENOMEM;
mutex_lock(&bpf_event_mutex);
ret = bpf_prog_array_copy_info(event->tp_event->prog_array,
- uquery->ids,
- query.ids_len,
- &uquery->prog_cnt);
+ ids,
+ ids_len,
+ &prog_cnt);
mutex_unlock(&bpf_event_mutex);
+ if (!ret || ret == -ENOSPC) {
+ if (copy_to_user(&uquery->prog_cnt, &prog_cnt,
sizeof(prog_cnt)) ||
+ copy_to_user(uquery->ids, ids, ids_len * sizeof(u32))) {
+ ret = -EFAULT;
+ goto out;
+ }
+ }
+
+out:
+ kfree(ids);
alloc/free just to avoid this locking dependency feels suboptimal.
may be we can get rid of bpf_event_mutex in some cases?
the perf event itself is locked via perf_event_ctx_lock() when we're
calling perf_event_query_prog_array, perf_event_attach|detach_bpf_prog.
I forgot what was the motivation for us to introduce it in the
first place.