[PATCH] selftest: Fix UB of getline due to missing var init

[Chris Gellermann <christian.gellermann@codasip.com>]

Clone3_set_tid uses getline(&line, &len, f) in a loop to read the
child's process status. The code expects that getline allocates the
buffer for the line on the first loop iteration. For this, glibc[1]
requires char *line to be set to NULL:

> ssize_t getline(char **restrict lineptr, ...)
> If *lineptr is set to NULL before the call, then getline() will
> allocate a buffer for storing the line.

However, char *line is only declared, leading to an undefined
initialization value. Fix this by properly initializing it to NULL.

Same issue fixed in mlock-random-test.

[1] https://man7.org/linux/man-pages/man3/getline.3.html

Fixes: 41585bbeeef9 ("selftests: add tests for clone3() with *set_tid")
Fixes: 26b4224d9961 ("selftests: expanding more mlock selftest")
Signed-off-by: Chris Gellermann <christian.gellermann@codasip.com>
---
 tools/testing/selftests/clone3/clone3_set_tid.c | 2 +-
 tools/testing/selftests/mm/mlock-random-test.c  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/clone3/clone3_set_tid.c b/tools/testing/selftests/clone3/clone3_set_tid.c
index 5c944aee6b41..485efa7c9eed 100644
--- a/tools/testing/selftests/clone3/clone3_set_tid.c
+++ b/tools/testing/selftests/clone3/clone3_set_tid.c
@@ -141,7 +141,7 @@ int main(int argc, char *argv[])
 {
 	FILE *f;
 	char buf;
-	char *line;
+	char *line = NULL;
 	int status;
 	int ret = -1;
 	size_t len = 0;
diff --git a/tools/testing/selftests/mm/mlock-random-test.c b/tools/testing/selftests/mm/mlock-random-test.c
index 9d349c151360..16294bc7dae6 100644
--- a/tools/testing/selftests/mm/mlock-random-test.c
+++ b/tools/testing/selftests/mm/mlock-random-test.c
@@ -84,7 +84,7 @@ int get_proc_locked_vm_size(void)
 int get_proc_page_size(unsigned long addr)
 {
 	FILE *smaps;
-	char *line;
+	char *line = NULL;
 	unsigned long mmupage_size = 0;
 	size_t size;
 
-- 
2.47.3