[34-longterm 141/260] KEYS: Fix RCU no-lock warning in keyctl_session_to_parent()

Paul Gortmaker
2011-01-02T07:24:07Z

From: David Howells <dhowells@redhat.com>

commit 9d1ac65a9698513d00e5608d93fca0c53f536c14 upstream.

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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
security/keys/keyctl.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index e9c2e7c..d29e022 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1259,6 +1259,7 @@ long keyctl_session_to_parent(void)
keyring_r = NULL;

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

parent = me->real_parent;
@@ -1313,6 +1314,7 @@ 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;
@@ -1321,6 +1323,7 @@ already_same:
ret = 0;
not_permitted:
write_unlock_irq(&tasklist_lock);
+ rcu_read_unlock();
put_cred(cred);
return ret;

--
1.7.3.3