Messages in this thread Patch in this message | | | Date | Wed, 18 Jul 2012 09:03:22 -0700 | From | Darren Hart <> | Subject | Re: potential NULL dereference in futex_wait_requeue_pi() |
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On 07/18/2012 07:25 AM, Dan Carpenter wrote: > Hi Darren, > > The patch 52400ba94675: "futex: add requeue_pi functionality" from > Apr 3, 2009, leads to the following warning: > kernel/futex.c:2373 futex_wait_requeue_pi() > error: potential NULL dereference 'pi_mutex'. > > 2330 if (!q.rt_waiter) { > 2331 /* > 2332 * Got the lock. We might not be the anticipated owner if we > 2333 * did a lock-steal - fix up the PI-state in that case. > 2334 */ > 2335 if (q.pi_state && (q.pi_state->owner != current)) { > 2336 spin_lock(q.lock_ptr); > 2337 ret = fixup_pi_state_owner(uaddr2, &q, current); > > pi_mutex is NULL here and it looks like fixup_pi_state_owner() can > return -EFAULT. > > > 2338 spin_unlock(q.lock_ptr); > 2339 } > 2340 } else { > > [snipped] > > 2366 } > 2367 > 2368 /* > 2369 * If fixup_pi_state_owner() faulted and was unable to handle the > 2370 * fault, unlock the rt_mutex and return the fault to userspace. > 2371 */ > 2372 if (ret == -EFAULT) { > 2373 if (rt_mutex_owner(pi_mutex) == current) > ^^^^^^^^ > This will oops if pi_mutex is NULL. > > 2374 rt_mutex_unlock(pi_mutex); > 2375 } else if (ret == -EINTR) {
Nice Dan, thanks for taking a closer look. This appears to be a simple fix, can you try the following:
futex: Test for pi_mutex on fault in futex_wait_requeue_pi
If fixup_pi_state_owner() faults, pi_mutex may be NULL. Test for pi_mutex != NULL before testing the owner against current and possibly unlocking it.
Signed-off-by: Darren Hart <dvhart@linux.intel.com> CC: Dave Jones <davej@redhat.com> CC: Dan Carpenter <dan.carpenter@oracle.com> CC: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/futex.c b/kernel/futex.c index e2b0fb9..05018bf 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -2370,7 +2370,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags, * fault, unlock the rt_mutex and return the fault to userspace. */ if (ret == -EFAULT) { - if (rt_mutex_owner(pi_mutex) == current) + if (pi_mutex && rt_mutex_owner(pi_mutex) == current) rt_mutex_unlock(pi_mutex); } else if (ret == -EINTR) { /*
-- Darren Hart Intel Open Source Technology Center Yocto Project - Linux Kernel
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