From: David Howells <dhowells@redhat.com>

Date: Fri, 10 Sep 2010 08:59:46 +0000 (+0100)

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

X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=9d1ac65a9698513d00e5608d93fca0c53f536c14

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>

---

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c

index b2b0998..3868c67 100644

--- a/security/keys/keyctl.c

+++ b/security/keys/keyctl.c

@@ -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;