tracehook: tracehook_tracer_task

This adds the tracehook_tracer_task() hook to consolidate all forms of
"Who is using ptrace on me?" logic.  This is used for "TracerPid:" in
/proc and for permission checks.  We also clean up the selinux code the
called an identical accessor.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Reviewed-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 37 insertions, 25 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 797d775e0354..0d6eb33597c6 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -80,6 +80,7 @@
 #include <linux/delayacct.h>
 #include <linux/seq_file.h>
 #include <linux/pid_namespace.h>
+#include <linux/tracehook.h>
 
 #include <asm/pgtable.h>
 #include <asm/processor.h>
@@ -168,8 +169,12 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
         rcu_read_lock();
         ppid = pid_alive(p) ?
                 task_tgid_nr_ns(rcu_dereference(p->real_parent), ns) : 0;
-        tpid = pid_alive(p) && p->ptrace ?
-                task_pid_nr_ns(rcu_dereference(p->parent), ns) : 0;
+        tpid = 0;
+        if (pid_alive(p)) {
+                struct task_struct *tracer = tracehook_tracer_task(p);
+                if (tracer)
+                        tpid = task_pid_nr_ns(tracer, ns);
+        }
         seq_printf(m,
                 "State:\t%s\n"
                 "Tgid:\t%d\n"
diff --git a/fs/proc/base.c b/fs/proc/base.c
index a891fe4cb43b..4b74dba69a6d 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -69,6 +69,7 @@
 #include <linux/mount.h>
 #include <linux/security.h>
 #include <linux/ptrace.h>
+#include <linux/tracehook.h>
 #include <linux/cgroup.h>
 #include <linux/cpuset.h>
 #include <linux/audit.h>
@@ -231,10 +232,14 @@ static int check_mem_permission(struct task_struct *task)
          * If current is actively ptrace'ing, and would also be
          * permitted to freshly attach with ptrace now, permit it.
          */
-        if (task->parent == current && (task->ptrace & PT_PTRACED) &&
-            task_is_stopped_or_traced(task) &&
-            ptrace_may_access(task, PTRACE_MODE_ATTACH))
-                return 0;
+        if (task_is_stopped_or_traced(task)) {
+                int match;
+                rcu_read_lock();
+                match = (tracehook_tracer_task(task) == current);
+                rcu_read_unlock();
+                if (match && ptrace_may_access(task, PTRACE_MODE_ATTACH))
+                        return 0;
+        }
 
         /*
          * Noone else is allowed.
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 9a5b3be2503a..6468ca0fe69b 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -73,6 +73,24 @@ static inline int tracehook_unsafe_exec(struct task_struct *task)
 }
 
 /**
+ * tracehook_tracer_task - return the task that is tracing the given task
+ * @tsk:                task to consider
+ *
+ * Returns NULL if noone is tracing @task, or the &struct task_struct
+ * pointer to its tracer.
+ *
+ * Must called under rcu_read_lock().  The pointer returned might be kept
+ * live only by RCU.  During exec, this may be called with task_lock()
+ * held on @task, still held from when tracehook_unsafe_exec() was called.
+ */
+static inline struct task_struct *tracehook_tracer_task(struct task_struct *tsk)
+{
+        if (task_ptrace(tsk) & PT_PTRACED)
+                return rcu_dereference(tsk->parent);
+        return NULL;
+}
+
+/**
  * tracehook_report_exec - a successful exec was completed
  * @fmt:                &struct linux_binfmt that performed the exec
  * @bprm:               &struct linux_binprm containing exec details
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 63f131fc42e4..3481cde5bf15 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -25,7 +25,7 @@
 
 #include <linux/init.h>
 #include <linux/kernel.h>
-#include <linux/ptrace.h>
+#include <linux/tracehook.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/security.h>
@@ -1971,22 +1971,6 @@ static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
         return __vm_enough_memory(mm, pages, cap_sys_admin);
 }
 
-/**
- * task_tracer_task - return the task that is tracing the given task
- * @task:               task to consider
- *
- * Returns NULL if noone is tracing @task, or the &struct task_struct
- * pointer to its tracer.
- *
- * Must be called under rcu_read_lock().
- */
-static struct task_struct *task_tracer_task(struct task_struct *task)
-{
-        if (task->ptrace & PT_PTRACED)
-                return rcu_dereference(task->parent);
-        return NULL;
-}
-
 /* binprm security operations */
 
 static int selinux_bprm_alloc_security(struct linux_binprm *bprm)
@@ -2238,7 +2222,7 @@ static void selinux_bprm_apply_creds(struct linux_binprm *bprm, int unsafe)
                         u32 ptsid = 0;
 
                         rcu_read_lock();
-                        tracer = task_tracer_task(current);
+                        tracer = tracehook_tracer_task(current);
                         if (likely(tracer != NULL)) {
                                 sec = tracer->security;
                                 ptsid = sec->sid;
@@ -5247,7 +5231,7 @@ static int selinux_setprocattr(struct task_struct *p,
                    Otherwise, leave SID unchanged and fail. */
                 task_lock(p);
                 rcu_read_lock();
-                tracer = task_tracer_task(p);
+                tracer = tracehook_tracer_task(p);
                 if (tracer != NULL) {
                         struct task_security_struct *ptsec = tracer->security;
                         u32 ptsid = ptsec->sid;