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>

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 0dde959..6fe7a5c 100644 (file)
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -666,11 +666,6 @@
  *     @sig contains the signal value.
  *     @secid contains the sid of the process where the signal originated
  *     Return 0 if permission is granted.
- * @task_wait:
- *     Check permission before allowing a process to reap a child process @p
- *     and collect its status information.
- *     @p contains the task_struct for process.
- *     Return 0 if permission is granted.
  * @task_prctl:
  *     Check permission before performing a process control operation on the
  *     current process.
@@ -1507,7 +1502,6 @@ union security_list_options {
        int (*task_movememory)(struct task_struct *p);
        int (*task_kill)(struct task_struct *p, struct siginfo *info,
                                int sig, u32 secid);
-       int (*task_wait)(struct task_struct *p);
        int (*task_prctl)(int option, unsigned long arg2, unsigned long arg3,
                                unsigned long arg4, unsigned long arg5);
        void (*task_to_inode)(struct task_struct *p, struct inode *inode);
@@ -1767,7 +1761,6 @@ struct security_hook_heads {
        struct list_head task_getscheduler;
        struct list_head task_movememory;
        struct list_head task_kill;
-       struct list_head task_wait;
        struct list_head task_prctl;
        struct list_head task_to_inode;
        struct list_head ipc_permission;

diff --git a/include/linux/security.h b/include/linux/security.h
index f4ebac1..d3868f2 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -332,7 +332,6 @@ int security_task_getscheduler(struct task_struct *p);
 int security_task_movememory(struct task_struct *p);
 int security_task_kill(struct task_struct *p, struct siginfo *info,
                        int sig, u32 secid);
-int security_task_wait(struct task_struct *p);
 int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                        unsigned long arg4, unsigned long arg5);
 void security_task_to_inode(struct task_struct *p, struct inode *inode);
@@ -980,11 +979,6 @@ static inline int security_task_kill(struct task_struct *p,
        return 0;
 }
 
-static inline int security_task_wait(struct task_struct *p)
-{
-       return 0;
-}
-
 static inline int security_task_prctl(int option, unsigned long arg2,
                                      unsigned long arg3,
                                      unsigned long arg4,

diff --git a/kernel/exit.c b/kernel/exit.c
index 8f14b86..60f2451 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -14,7 +14,6 @@
 #include <linux/tty.h>
 #include <linux/iocontext.h>
 #include <linux/key.h>
-#include <linux/security.h>
 #include <linux/cpu.h>
 #include <linux/acct.h>
 #include <linux/tsacct_kern.h>
@@ -1360,7 +1359,7 @@ static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
  * Returns nonzero for a final return, when we have unlocked tasklist_lock.
  * Returns zero if the search for a child should continue;
  * then ->notask_error is 0 if @p is an eligible child,
- * or another error from security_task_wait(), or still -ECHILD.
+ * or still -ECHILD.
  */
 static int wait_consider_task(struct wait_opts *wo, int ptrace,
                                struct task_struct *p)
@@ -1380,20 +1379,6 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
        if (!ret)
                return ret;
 
-       ret = security_task_wait(p);
-       if (unlikely(ret < 0)) {
-               /*
-                * If we have not yet seen any eligible child,
-                * then let this error code replace -ECHILD.
-                * A permission error will give the user a clue
-                * to look for security policy problems, rather
-                * than for mysterious wait bugs.
-                */
-               if (wo->notask_error)
-                       wo->notask_error = ret;
-               return 0;
-       }
-
        if (unlikely(exit_state == EXIT_TRACE)) {
                /*
                 * ptrace == 0 means we are the natural parent. In this case
@@ -1486,7 +1471,7 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
  * Returns nonzero for a final return, when we have unlocked tasklist_lock.
  * Returns zero if the search for a child should continue; then
  * ->notask_error is 0 if there were any eligible children,
- * or another error from security_task_wait(), or still -ECHILD.
+ * or still -ECHILD.
  */
 static int do_wait_thread(struct wait_opts *wo, struct task_struct *tsk)
 {

diff --git a/security/security.c b/security/security.c
index 32052f5..8c9fee5 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -1025,11 +1025,6 @@ int security_task_kill(struct task_struct *p, struct siginfo *info,
        return call_int_hook(task_kill, 0, p, info, sig, secid);
 }
 
-int security_task_wait(struct task_struct *p)
-{
-       return call_int_hook(task_wait, 0, p);
-}
-
 int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                         unsigned long arg4, unsigned long arg5)
 {
@@ -1769,7 +1764,6 @@ struct security_hook_heads security_hook_heads = {
        .task_movememory =
                LIST_HEAD_INIT(security_hook_heads.task_movememory),
        .task_kill =    LIST_HEAD_INIT(security_hook_heads.task_kill),
-       .task_wait =    LIST_HEAD_INIT(security_hook_heads.task_wait),
        .task_prctl =   LIST_HEAD_INIT(security_hook_heads.task_prctl),
        .task_to_inode =
                LIST_HEAD_INIT(security_hook_heads.task_to_inode),

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 55ad878..a5398fe 100644 (file)
--- 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),

diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 8da4a6b..2166373 100644 (file)
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2271,25 +2271,6 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
        return rc;
 }
 
-/**
- * smack_task_wait - Smack access check for waiting
- * @p: task to wait for
- *
- * Returns 0
- */
-static int smack_task_wait(struct task_struct *p)
-{
-       /*
-        * Allow the operation to succeed.
-        * Zombies are bad.
-        * In userless environments (e.g. phones) programs
-        * get marked with SMACK64EXEC and even if the parent
-        * and child shouldn't be talking the parent still
-        * may expect to know when the child exits.
-        */
-       return 0;
-}
-
 /**
  * smack_task_to_inode - copy task smack into the inode blob
  * @p: task to copy from
@@ -4658,7 +4639,6 @@ static struct security_hook_list smack_hooks[] = {
        LSM_HOOK_INIT(task_getscheduler, smack_task_getscheduler),
        LSM_HOOK_INIT(task_movememory, smack_task_movememory),
        LSM_HOOK_INIT(task_kill, smack_task_kill),
-       LSM_HOOK_INIT(task_wait, smack_task_wait),
        LSM_HOOK_INIT(task_to_inode, smack_task_to_inode),
 
        LSM_HOOK_INIT(ipc_permission, smack_ipc_permission),