[PATCH v2 2/2] selftests/mm: Fix potential wild pointer access of getline due to missing init

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

This is another occurrence of using getline where the code assumes that
getline allocates memory to store the line, but the pointer passed to
it is uninitialized and potentially a non-null pointer. This
violates the Open Group Spec[1] and caused a segfault in a similar
situation in selftest/clone3/clone3_set_tid. Fix it by initializing the
line pointer to NULL.

The issue has been found by simply grepping through the selftest code
after running into the issue in clone3_set_tid. Whether it segfaults in
its current state is unknown to me. But it's good to be addressed due to
defensive reasons.

[1] https://pubs.opengroup.org/onlinepubs/9799919799/functions/getline.html

Fixes: 26b4224d9961 ("selftests: expanding more mlock selftest")
Cc: stable@vger.kernel.org
Acked-by: David Hildenbrand (arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Signed-off-by: Chris Gellermann <christian.gellermann@codasip.com>
---
 tools/testing/selftests/mm/mlock-random-test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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