bpf: fix bpf_perf_event_read() helper

Fix safety checks for bpf_perf_event_read():
- only non-inherited events can be added to perf_event_array map
  (do this check statically at map insertion time)
- dynamically check that event is local and !pmu->count
Otherwise buggy bpf program can cause kernel splat.

Also fix error path after perf_event_attrs()
and remove redundant 'extern'.

Fixes: 35578d79 ("bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Wang Nan <wangnan0@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/bpf.h

@@ -194,7 +194,6 @@ extern const struct bpf_func_proto bpf_map_lookup_elem_proto;
 extern const struct bpf_func_proto bpf_map_update_elem_proto;
 extern const struct bpf_func_proto bpf_map_delete_elem_proto;
 
-extern const struct bpf_func_proto bpf_perf_event_read_proto;
 extern const struct bpf_func_proto bpf_get_prandom_u32_proto;
 extern const struct bpf_func_proto bpf_get_smp_processor_id_proto;
 extern const struct bpf_func_proto bpf_tail_call_proto;

kernel/bpf/arraymap.c

@@ -292,16 +292,23 @@ static void *perf_event_fd_array_get_ptr(struct bpf_map *map, int fd)
 
 	attr = perf_event_attrs(event);
 	if (IS_ERR(attr))
-		return (void *)attr;
+		goto err;
 
-	if (attr->type != PERF_TYPE_RAW &&
-	    !(attr->type == PERF_TYPE_SOFTWARE &&
-	      attr->config == PERF_COUNT_SW_BPF_OUTPUT) &&
-	    attr->type != PERF_TYPE_HARDWARE) {
+	if (attr->inherit)
+		goto err;
+
+	if (attr->type == PERF_TYPE_RAW)
+		return event;
+
+	if (attr->type == PERF_TYPE_HARDWARE)
+		return event;
+
+	if (attr->type == PERF_TYPE_SOFTWARE &&
+	    attr->config == PERF_COUNT_SW_BPF_OUTPUT)
+		return event;
+err:
 	perf_event_release_kernel(event);
 	return ERR_PTR(-EINVAL);
-	}
-	return event;
 }
 
 static void perf_event_fd_array_put_ptr(void *ptr)

kernel/trace/bpf_trace.c

@@ -199,6 +199,11 @@ static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
 	if (!event)
 		return -ENOENT;
 
+	/* make sure event is local and doesn't have pmu::count */
+	if (event->oncpu != smp_processor_id() ||
+	    event->pmu->count)
+		return -EINVAL;
+
 	/*
 	 * we don't know if the function is run successfully by the
 	 * return value. It can be judged in other places, such as
@@ -207,7 +212,7 @@ static u64 bpf_perf_event_read(u64 r1, u64 index, u64 r3, u64 r4, u64 r5)
 	return perf_event_read_local(event);
 }
 
-const struct bpf_func_proto bpf_perf_event_read_proto = {
+static const struct bpf_func_proto bpf_perf_event_read_proto = {
 	.func		= bpf_perf_event_read,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,