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KEYS: Fix RCU no-lock warning in keyctl_session_to_parent()
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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 <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
dhowells authored and torvalds committed Sep 10, 2010
1 parent ff3cb3f commit 9d1ac65
Showing 1 changed file with 3 additions and 0 deletions.
3 changes: 3 additions & 0 deletions security/keys/keyctl.c
Original file line number Diff line number Diff line change
@@ -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 @@ long keyctl_session_to_parent(void)
ret = 0;
not_permitted:
write_unlock_irq(&tasklist_lock);
rcu_read_unlock();
put_cred(cred);
return ret;

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