proc: hold cred_guard_mutex in check_mem_permission()
Avoid a potential race when task exec's and we get a new ->mm but check against
the old credentials in ptrace_may_access().
Holding of the mutex is implemented by factoring out the body of the code into a
helper function __check_mem_permission(). Performing this factorization now
simplifies upcoming changes and minimizes churn in the diff's.
Signed-off-by: Stephen Wilson <wilsons@start.ca>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9af49a3..013f116 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -191,10 +191,7 @@
return result;
}
-/*
- * Return zero if current may access user memory in @task, -error if not.
- */
-static int check_mem_permission(struct task_struct *task)
+static int __check_mem_permission(struct task_struct *task)
{
/*
* A task can always look at itself, in case it chooses
@@ -222,6 +219,27 @@
return -EPERM;
}
+/*
+ * Return zero if current may access user memory in @task, -error if not.
+ */
+static int check_mem_permission(struct task_struct *task)
+{
+ int err;
+
+ /*
+ * Avoid racing if task exec's as we might get a new mm but validate
+ * against old credentials.
+ */
+ err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (err)
+ return err;
+
+ err = __check_mem_permission(task);
+ mutex_unlock(&task->signal->cred_guard_mutex);
+
+ return err;
+}
+
struct mm_struct *mm_for_maps(struct task_struct *task)
{
struct mm_struct *mm;