[CRIU] [PATCH] sieze: fix NULL pointer dereference in freezer_detach

[Stanislav Kinsburskiy]

Below is the NULL pointer call trace for freezer_detach:

ct_dump_finish
    pstree_switch_state
        freezer_detach ---> dereference of processes_to_wait_pids

But ct_dump_finish is also called on all the error paths in cr_dump_tasks, and
can be called _before_ collect_pstree, which initializes
processes_to_wait_pids in freezer_wait_processes.

This patch add exit from freezer_detach if processes_to_wait_pids is NULL.

Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
---
 criu/seize.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/criu/seize.c b/criu/seize.c
index 0ea7a28..82755a7 100644
--- a/criu/seize.c
+++ b/criu/seize.c
@@ -221,6 +221,9 @@ static int freezer_detach(void)
 	if (!opts.freeze_cgroup)
 		return 0;
 
+	if (!processes_to_wait_pids)
+		return 0;
+
 	for (i = 0; i < processes_to_wait && processes_to_wait_pids; i++) {
 		pid_t pid = processes_to_wait_pids[i];
 		int status, save_errno;