[LTP] [PATCH v2] cgroup_core02: Allocate child stack using mmap()

[Martin Doucha]

Some architectures like arm64 have strict requirements for stack alignment.
Statically allocated buffer may result in one of the test processes
getting killed by SIGBUS. Allocate child stack using mmap() to ensure
the requirements are met.

Signed-off-by: Martin Doucha <mdoucha@suse.cz>
Acked-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
---

Changes since v1: Added #define for stack size

I've also verified that the CVE is still reproducible on affected kernels
with this test fix.

 testcases/kernel/controllers/cgroup/cgroup_core02.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/testcases/kernel/controllers/cgroup/cgroup_core02.c b/testcases/kernel/controllers/cgroup/cgroup_core02.c
index 733e88ee7..b19bf2e58 100644
--- a/testcases/kernel/controllers/cgroup/cgroup_core02.c
+++ b/testcases/kernel/controllers/cgroup/cgroup_core02.c
@@ -32,6 +32,8 @@
 #include "tst_safe_file_at.h"
 #include "lapi/sched.h"
 
+#define STACK_SIZE 65536
+
 static struct tst_cg_group *cg_child_a, *cg_child_b;
 static uid_t nobody_uid;
 
@@ -51,7 +53,7 @@ static int lesser_ns_open_thread_fn(void *arg)
 static void test_lesser_ns_open(void)
 {
 	int i;
-	static char stack[65536];
+	char *stack;
 	pid_t pid;
 	int status;
 	struct lesser_ns_open_thread_arg targ = { .fds = {0}, .loops = -1};
@@ -63,14 +65,19 @@ static void test_lesser_ns_open(void)
 		SAFE_CG_PRINT(cg_child_a, "cgroup.procs", "0");
 		SAFE_CG_FCHOWN(cg_child_a, "cgroup.procs",  nobody_uid, -1);
 		SAFE_CG_FCHOWN(cg_child_b, "cgroup.procs",  nobody_uid, -1);
+		stack = SAFE_MMAP(NULL, STACK_SIZE, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
 		pid  = ltp_clone(CLONE_NEWCGROUP | CLONE_FILES | CLONE_VM | SIGCHLD,
-					lesser_ns_open_thread_fn, &targ, 65536, stack);
+					lesser_ns_open_thread_fn, &targ, STACK_SIZE, stack);
+
 		if (pid < 0)  {
 			tst_res(TFAIL, "unexpected negative pid %d", pid);
 			exit(1);
 		}
 
 		SAFE_WAITPID(pid, &status, 0);
+		SAFE_MUNMAP(stack, STACK_SIZE);
+
 		for (i = 0; i < targ.loops; i++) {
 			if (targ.fds[i] < 1) {
 				tst_res(TFAIL, "unexpected negative fd %d", targ.fds[i]);
-- 
2.47.0