tracing/probes: Fix to add NULL check for BTF APIs

Since find_btf_func_param() abd btf_type_by_id() can return NULL,
the caller must check the return value correctly.

Link: https://lore.kernel.org/all/169024903951.395371.11361556840733470934.stgit@devnote2/

Fixes: b576e097 ("tracing/probes: Support function parameters if BTF is available")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace_probe.c

@@ -386,12 +386,12 @@ static const struct btf_type *find_btf_func_proto(const char *funcname)
 
 	/* Get BTF_KIND_FUNC type */
 	t = btf_type_by_id(btf, id);
-	if (!btf_type_is_func(t))
+	if (!t || !btf_type_is_func(t))
 		return ERR_PTR(-ENOENT);
 
 	/* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
 	t = btf_type_by_id(btf, t->type);
-	if (!btf_type_is_func_proto(t))
+	if (!t || !btf_type_is_func_proto(t))
 		return ERR_PTR(-ENOENT);
 
 	return t;
@@ -443,7 +443,7 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
 	if (!ctx->params) {
 		params = find_btf_func_param(ctx->funcname, &ctx->nr_params,
 					     ctx->flags & TPARG_FL_TPOINT);
-		if (IS_ERR(params)) {
+		if (IS_ERR_OR_NULL(params)) {
 			trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
 			return PTR_ERR(params);
 		}
@@ -1273,7 +1273,7 @@ const char **traceprobe_expand_meta_args(int argc, const char *argv[],
 
 	params = find_btf_func_param(ctx->funcname, &nr_params,
 				     ctx->flags & TPARG_FL_TPOINT);
-	if (IS_ERR(params)) {
+	if (IS_ERR_OR_NULL(params)) {
 		if (args_idx != -1) {
 			/* $arg* requires BTF info */
 			trace_probe_log_err(0, NOSUP_BTFARG);