On 1/10/2017 9:28 AM, Stephen Smalley wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Stephen Smalley <sds@xxxxxxxxxxxxx>
Acked-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
> ---
> include/linux/lsm_hooks.h | 7 -------
> include/linux/security.h | 6 ------
> kernel/exit.c | 19 ++-----------------
> security/security.c | 6 ------
> security/selinux/hooks.c | 7 -------
> security/smack/smack_lsm.c | 20 --------------------
> 6 files changed, 2 insertions(+), 63 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 0dde959..6fe7a5c 100644
> --- 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
> --- 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
> --- 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
> --- 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 bada3cd..720dbd0 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3969,12 +3969,6 @@ 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)
> {
> @@ -6217,7 +6211,6 @@ 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
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -2272,25 +2272,6 @@ static int smack_task_kill(struct task_struct *p, struct siginfo *info,
> }
>
> /**
> - * 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
> * @inode: inode to copy to
> @@ -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),
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