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

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commit 91af8300d9 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>
This commit is contained in:
Coly Li 2017-10-13 16:35:29 -07:00 committed by Greg Kroah-Hartman
parent a1e25420a4
commit 770e10817e
1 changed files with 2 additions and 1 deletions
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3
drivers/md/bcache/alloc.c
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@ -404,7 +404,8 @@ 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);