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 <col...@suse.de>
Reported-by: Jorg Bornschein <j...@capsec.org>
Cc: Kent Overstreet <kent.overstr...@gmail.com>
Cc: sta...@vger.kernel.org
---
drivers/md/bcache/alloc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
index cacbe2dbd5c3..e1a4205caa2e 100644
--- a/drivers/md/bcache/alloc.c
+++ b/drivers/md/bcache/alloc.c
@@ -406,7 +406,8 @@ long bch_bucket_alloc(struct cache *ca, unsigned reserve,
bool wait)
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);
--
2.13.5
