linux-kernel - [PATCH 3.16 022/136] bcache: check ca->alloc

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Date:   Sun, 11 Feb 2018 04:31:11 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jens Axboe" <axboe@...nel.dk>,
        "Michael Lyle" <mlyle@...e.org>,
        "Kent Overstreet" <kent.overstreet@...il.com>,
        "Jorg Bornschein" <jb@...sec.org>, "Coly Li" <colyli@...e.de>
Subject: [PATCH 3.16 022/136] bcache: check ca->alloc_thread initialized
 before wake up it

3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Coly Li <colyli@...e.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@...e.de>
Reported-by: Jorg Bornschein <jb@...sec.org>
Cc: Kent Overstreet <kent.overstreet@...il.com>
Reviewed-by: Michael Lyle <mlyle@...e.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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);