[093/152] md: protect against NULL reference when waiting to start a raid10.

Greg KH
2011-01-06T00:30:44Z

From: NeilBrown <neilb@suse.de>

commit 589a594be1fb8815b3f18e517be696c48664f728 upstream.

When we fail to start a raid10 for some reason, we call
md_unregister_thread to kill the thread that was created.

Unfortunately md_thread() will then make one call into the handler
(raid10d) even though md_wakeup_thread has not been called. This is
not safe and as md_unregister_thread is called after mddev->private
has been set to NULL, it will definitely cause a NULL dereference.

So fix this at both ends:
- md_thread should only call the handler if THREAD_WAKEUP has been
set.
- raid10 should call md_unregister_thread before setting things
to NULL just like all the other raid modules do.

This is applicable to 2.6.35 and later.

Reported-by: "Citizen" <citizen_lee@thecus.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/md/md.c | 5 ++---
drivers/md/raid10.c | 2 +-
2 files changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6040,9 +6040,8 @@ static int md_thread(void * arg)
|| kthread_should_stop(),
thread->timeout);

- clear_bit(THREAD_WAKEUP, &thread->flags);
-
- thread->run(thread->mddev);
+ if (test_and_clear_bit(THREAD_WAKEUP, &thread->flags))
+ thread->run(thread->mddev);
}

return 0;
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2396,13 +2396,13 @@ static int run(mddev_t *mddev)
return 0;

out_free_conf:
+ md_unregister_thread(mddev->thread);
if (conf->r10bio_pool)
mempool_destroy(conf->r10bio_pool);
safe_put_page(conf->tmppage);
kfree(conf->mirrors);
kfree(conf);
mddev->private = NULL;
- md_unregister_thread(mddev->thread);
out:
return -EIO;
}