security,selinux,smack: kill security_task_wait hook

As reported by yangshukui, a permission denial from security_task_wait()
can lead to a soft lockup in zap_pid_ns_processes() since it only expects
sys_wait4() to return 0 or -ECHILD. Further, security_task_wait() can
in general lead to zombies; in the absence of some way to automatically
reparent a child process upon a denial, the hook is not useful.  Remove
the security hook and its implementations in SELinux and Smack.  Smack
already removed its check from its hook.

Reported-by: yangshukui <yangshukui@huawei.com>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 0 insertions, 7 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 55ad878f1146..a5398fea0966 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3963,12 +3963,6 @@ static int selinux_task_kill(struct task_struct *p, struct siginfo *info,
         return avc_has_perm(secid, task_sid(p), SECCLASS_PROCESS, perm, NULL);
 }
 
-static int selinux_task_wait(struct task_struct *p)
-{
-        return avc_has_perm(task_sid(p), current_sid(), SECCLASS_PROCESS,
-                            PROCESS__SIGCHLD, NULL);
-}
-
 static void selinux_task_to_inode(struct task_struct *p,
                                   struct inode *inode)
 {
@@ -6211,7 +6205,6 @@ static struct security_hook_list selinux_hooks[] = {
         LSM_HOOK_INIT(task_getscheduler, selinux_task_getscheduler),
         LSM_HOOK_INIT(task_movememory, selinux_task_movememory),
         LSM_HOOK_INIT(task_kill, selinux_task_kill),
-        LSM_HOOK_INIT(task_wait, selinux_task_wait),
         LSM_HOOK_INIT(task_to_inode, selinux_task_to_inode),
 
         LSM_HOOK_INIT(ipc_permission, selinux_ipc_permission),