audit: Call tty_audit_push_task() outside preempt disabled
While auditing all tasklist_lock read_lock sites I stumbled over the
following call chain:
audit_prepare_user_tty()
read_lock(&tasklist_lock);
tty_audit_push_task();
mutex_lock(&buf->mutex);
--> buf->mutex is locked with preemption disabled.
Solve this by acquiring a reference to the task struct under
rcu_read_lock and call tty_audit_push_task outside of the preempt
disabled region.
Move all code which needs to be protected by sighand lock into
tty_audit_push_task() and use lock/unlock_sighand as we do not hold
tasklist_lock.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric Paris <eparis@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/char/tty_audit.c b/drivers/char/tty_audit.c
index 1b8ee59..f64582b 100644
--- a/drivers/char/tty_audit.c
+++ b/drivers/char/tty_audit.c
@@ -188,25 +188,43 @@
}
/**
- * tty_audit_push_task - Flush task's pending audit data
+ * tty_audit_push_task - Flush task's pending audit data
+ * @tsk: task pointer
+ * @loginuid: sender login uid
+ * @sessionid: sender session id
+ *
+ * Called with a ref on @tsk held. Try to lock sighand and get a
+ * reference to the tty audit buffer if available.
+ * Flush the buffer or return an appropriate error code.
*/
-void tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
+int tty_audit_push_task(struct task_struct *tsk, uid_t loginuid, u32 sessionid)
{
- struct tty_audit_buf *buf;
+ struct tty_audit_buf *buf = ERR_PTR(-EPERM);
+ unsigned long flags;
- spin_lock_irq(&tsk->sighand->siglock);
- buf = tsk->signal->tty_audit_buf;
- if (buf)
- atomic_inc(&buf->count);
- spin_unlock_irq(&tsk->sighand->siglock);
- if (!buf)
- return;
+ if (!lock_task_sighand(tsk, &flags))
+ return -ESRCH;
+
+ if (tsk->signal->audit_tty) {
+ buf = tsk->signal->tty_audit_buf;
+ if (buf)
+ atomic_inc(&buf->count);
+ }
+ unlock_task_sighand(tsk, &flags);
+
+ /*
+ * Return 0 when signal->audit_tty set
+ * but tsk->signal->tty_audit_buf == NULL.
+ */
+ if (!buf || IS_ERR(buf))
+ return PTR_ERR(buf);
mutex_lock(&buf->mutex);
tty_audit_buf_push(tsk, loginuid, sessionid, buf);
mutex_unlock(&buf->mutex);
tty_audit_buf_put(buf);
+ return 0;
}
/**
diff --git a/include/linux/tty.h b/include/linux/tty.h
index e500171..2a75474 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -541,8 +541,8 @@
extern void tty_audit_fork(struct signal_struct *sig);
extern void tty_audit_tiocsti(struct tty_struct *tty, char ch);
extern void tty_audit_push(struct tty_struct *tty);
-extern void tty_audit_push_task(struct task_struct *tsk,
- uid_t loginuid, u32 sessionid);
+extern int tty_audit_push_task(struct task_struct *tsk,
+ uid_t loginuid, u32 sessionid);
#else
static inline void tty_audit_add_data(struct tty_struct *tty,
unsigned char *data, size_t size)
@@ -560,9 +560,10 @@
static inline void tty_audit_push(struct tty_struct *tty)
{
}
-static inline void tty_audit_push_task(struct task_struct *tsk,
- uid_t loginuid, u32 sessionid)
+static inline int tty_audit_push_task(struct task_struct *tsk,
+ uid_t loginuid, u32 sessionid)
{
+ return 0;
}
#endif
diff --git a/kernel/audit.c b/kernel/audit.c
index a300931..8429afe 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -467,23 +467,16 @@
struct task_struct *tsk;
int err;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
tsk = find_task_by_vpid(pid);
- err = -ESRCH;
- if (!tsk)
- goto out;
- err = 0;
-
- spin_lock_irq(&tsk->sighand->siglock);
- if (!tsk->signal->audit_tty)
- err = -EPERM;
- spin_unlock_irq(&tsk->sighand->siglock);
- if (err)
- goto out;
-
- tty_audit_push_task(tsk, loginuid, sessionid);
-out:
- read_unlock(&tasklist_lock);
+ if (!tsk) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
+ get_task_struct(tsk);
+ rcu_read_unlock();
+ err = tty_audit_push_task(tsk, loginuid, sessionid);
+ put_task_struct(tsk);
return err;
}
