Commit 9d1ac65a authored Sep 10, 2010 by David Howells Committed by Linus Torvalds Sep 10, 2010

KEYS: Fix RCU no-lock warning in keyctl_session_to_parent()



There's an protected access to the parent process's credentials in the middle
of keyctl_session_to_parent().  This results in the following RCU warning:

  ===================================================
  [ INFO: suspicious rcu_dereference_check() usage. ]
  ---------------------------------------------------
  security/keys/keyctl.c:1291 invoked rcu_dereference_check() without protection!

  other info that might help us debug this:

  rcu_scheduler_active = 1, debug_locks = 0
  1 lock held by keyctl-session-/2137:
   #0:  (tasklist_lock){.+.+..}, at: [<ffffffff811ae2ec>] keyctl_session_to_parent+0x60/0x236

  stack backtrace:
  Pid: 2137, comm: keyctl-session- Not tainted 2.6.36-rc2-cachefs+ #1
  Call Trace:
   [<ffffffff8105606a>] lockdep_rcu_dereference+0xaa/0xb3
   [<ffffffff811ae379>] keyctl_session_to_parent+0xed/0x236
   [<ffffffff811af77e>] sys_keyctl+0xb4/0xb6
   [<ffffffff81001eab>] system_call_fastpath+0x16/0x1b

The code should take the RCU read lock to make sure the parents credentials
don't go away, even though it's holding a spinlock and has IRQ disabled.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ff3cb3fe

security/keys/keyctl.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1272,6 +1272,7 @@ long keyctl_session_to_parent(void)
		keyring_r = NULL;

		me = current;
		rcu_read_lock();
		write_lock_irq(&tasklist_lock);

		parent = me->real_parent;
		@@ -1319,6 +1320,7 @@ long keyctl_session_to_parent(void)
		set_ti_thread_flag(task_thread_info(parent), TIF_NOTIFY_RESUME);

		write_unlock_irq(&tasklist_lock);
		rcu_read_unlock();
		if (oldcred)
		put_cred(oldcred);
		return 0;
		@@ -1327,6 +1329,7 @@ already_same:
		ret = 0;
		not_permitted:
		write_unlock_irq(&tasklist_lock);
		rcu_read_unlock();
		put_cred(cred);
		return ret;

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