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Subject[PATCH 08/23] tracehook: tracehook_tracer_task
Date
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>
---
fs/proc/array.c | 9 +++++++--
fs/proc/base.c | 13 +++++++++----
include/linux/tracehook.h | 18 ++++++++++++++++++
security/selinux/hooks.c | 22 +++-------------------
4 files changed, 37 insertions(+), 25 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 797d775..0d6eb33 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 58c3e6a..6f21daa 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 9a5b3be..6468ca0 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 63f131f..3481cde 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;

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