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author | Thomas Gleixner <tglx@linutronix.de> | 2009-12-10 00:52:51 +0000 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2009-12-10 23:04:11 +0100 |
commit | d4581a239a40319205762b76c01eb6363f277efa (patch) | |
tree | d05b5f7103c9585e8485b581dc90f5a4ed9d18e3 /arch/x86/xen | |
parent | 7cf7db8df0b78076eafa4ead47559344ca7b7a43 (diff) |
sys: Fix missing rcu protection for __task_cred() access
commit c69e8d9 (CRED: Use RCU to access another task's creds and to
release a task's own creds) added non rcu_read_lock() protected access
to task creds of the target task in set_prio_one().
The comment above the function says:
* - the caller must hold the RCU read lock
The calling code in sys_setpriority does read_lock(&tasklist_lock) but
not rcu_read_lock(). This works only when CONFIG_TREE_PREEMPT_RCU=n.
With CONFIG_TREE_PREEMPT_RCU=y the rcu_callbacks can run in the tick
interrupt when they see no read side critical section.
There is another instance of __task_cred() in sys_setpriority() itself
which is equally unprotected.
Wrap the whole code section into a rcu read side critical section to
fix this quick and dirty.
Will be revisited in course of the read_lock(&tasklist_lock) -> rcu
crusade.
Oleg noted further:
This also fixes another bug here. find_task_by_vpid() is not safe
without rcu_read_lock(). I do not mean it is not safe to use the
result, just find_pid_ns() by itself is not safe.
Usually tasklist gives enough protection, but if copy_process() fails
it calls free_pid() lockless and does call_rcu(delayed_put_pid().
This means, without rcu lock find_pid_ns() can't scan the hash table
safely.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091210004703.029784964@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'arch/x86/xen')
0 files changed, 0 insertions, 0 deletions