tracing/probes: check the return value of kstrndup() for pbuf

kstrndup() is a memory allocation-related function, it returns NULL when
some internal memory errors happen. It is better to check the return
value of it so to catch the memory error in time.

Link: https://lkml.kernel.org/r/tencent_4D6E270731456EB88712ED7F13883C334906@qq.comAcked-by: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: a42e3c4d ("tracing/probe: Add immediate string parameter support")
Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_probe.c

@@ -356,6 +356,8 @@ static int __parse_imm_string(char *str, char **pbuf, int offs)
 		return -EINVAL;
 	}
 	*pbuf = kstrndup(str, len - 1, GFP_KERNEL);
+	if (!*pbuf)
+		return -ENOMEM;
 	return 0;
 }