The malloc() function may return NULL when it fails,
which may cause null pointer deference in prepare_exec_cmd(),
add Null check for return value of malloc().

Found by our static analysis tool.

Signed-off-by: Chenyuan Mi <cymi20@fudan.edu.cn>
---
 tools/lib/subcmd/exec-cmd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/lib/subcmd/exec-cmd.c b/tools/lib/subcmd/exec-cmd.c
index 5dbea456973e..2e45c0cd4b68 100644
--- a/tools/lib/subcmd/exec-cmd.c
+++ b/tools/lib/subcmd/exec-cmd.c
@@ -168,6 +168,8 @@ static const char **prepare_exec_cmd(const char **argv)
 	for (argc = 0; argv[argc]; argc++)
 		; /* just counting */
 	nargv = malloc(sizeof(*nargv) * (argc + 2));
+	if (!nargv)
+		return NULL;
 
 	nargv[0] = subcmd_config.exec_name;
 	for (argc = 0; argv[argc]; argc++)
-- 
2.17.1