Patch "bcache: check ca->alloc_thread initialized before wake up it" has been added to the 3.18-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    bcache: check ca->alloc_thread initialized before wake up it

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bcache-check-ca-alloc_thread-initialized-before-wake-up-it.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 91af8300d9c1d7c6b6a2fd754109e08d4798b8d8 Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Fri, 13 Oct 2017 16:35:29 -0700
Subject: bcache: check ca->alloc_thread initialized before wake up it

From: Coly Li <colyli@suse.de>

commit 91af8300d9c1d7c6b6a2fd754109e08d4798b8d8 upstream.

In bcache code, sysfs entries are created before all resources get
allocated, e.g. allocation thread of a cache set.

There is posibility for NULL pointer deference if a resource is accessed
but which is not initialized yet. Indeed Jorg Bornschein catches one on
cache set allocation thread and gets a kernel oops.

The reason for this bug is, when bch_bucket_alloc() is called during
cache set registration and attaching, ca->alloc_thread is not properly
allocated and initialized yet, call wake_up_process() on ca->alloc_thread
triggers NULL pointer deference failure. A simple and fast fix is, before
waking up ca->alloc_thread, checking whether it is allocated, and only
wake up ca->alloc_thread when it is not NULL.

Signed-off-by: Coly Li <colyli@suse.de>
Reported-by: Jorg Bornschein <jb@capsec.org>
Cc: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Michael Lyle <mlyle@lyle.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/bcache/alloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -406,7 +406,8 @@ long bch_bucket_alloc(struct cache *ca,
 
 	finish_wait(&ca->set->bucket_wait, &w);
 out:
-	wake_up_process(ca->alloc_thread);
+	if (ca->alloc_thread)
+		wake_up_process(ca->alloc_thread);
 
 	trace_bcache_alloc(ca, reserve);
 


Patches currently in stable-queue which might be from colyli@suse.de are

queue-3.18/bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch
queue-3.18/bcache-check-ca-alloc_thread-initialized-before-wake-up-it.patch