From: NeilBrown <neilb@suse.com>
To: Andrew Morton <akpm@linux-foundation.org>,
David Howells <dhowells@redhat.com>
Cc: Anthony DeRobertis <aderobertis@metrics.net>
Cc: linux-cachefs@redhat.com, linux-kernel@vger.kernel.org
Cc: Lei Xue <carmark.dlut@gmail.com>
Cc: Vegard Nossum <vegard.nossum@gmail.com>
Subject: [PATCH] cachefiles: fix multiple-put race.
Date: Wed, 04 Jul 2018 10:10:39 +1000 [thread overview]
Message-ID: <877emb2740.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <afbfd186-1f06-a03c-79b5-c98a12d35c75@metrics.net>
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cachefiles_read_waiter() owns a reference to a 'monitor'
object and adds the object to a 'to_do' list *before*
calling fscache_enqueue_retrieval() on it.
The reference is passed to the to_do list, so
cachefiles_read_waiter() no longer owns a reference and shouldn't be
accessing the monitor.
cachefiles_read_copier(), which handles the to_do list, might call
fscache_put_retrieval() *before* fscache_enqueue_retrieval()
takes its own reference.
This can result in fscache_put_retrieval() trying to discard the op
twice, which triggers an assertion failure, and can result in freed
memory be accessed.
The former looks like:
FS-Cache:
FS-Cache: Assertion failed
FS-Cache: 6 == 5 is false
------------[ cut here ]------------
kernel BUG at fs/fscache/operation.c:494!
A previous patch from Lei Xue moved the fscache_enqueue_retrieval()
call inside the spin_locked region. I think it is cleaner to move it
before.
Reported-by: Lei Xue <carmark.dlut@gmail.com>
Reported-by: Vegard Nossum <vegard.nossum@gmail.com>
Reported-by: Anthony DeRobertis <aderobertis@metrics.net>
Signed-off-by: NeilBrown <neilb@suse.com>
---
hi Andrew,
this issue was first mentioned in
https://lkml.org/lkml/2018/2/22/82
in February, but David Howells doesn't seem to have responded.
Can you take the patch?
Thanks,
NeilBrown
fs/cachefiles/rdwr.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index 5082c8a49686..553a71a2c9cb 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -56,11 +56,12 @@ static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
object = container_of(monitor->op->op.object,
struct cachefiles_object, fscache);
+ fscache_enqueue_retrieval(monitor->op);
+
spin_lock(&object->work_lock);
list_add_tail(&monitor->op_link, &monitor->op->to_do);
spin_unlock(&object->work_lock);
- fscache_enqueue_retrieval(monitor->op);
return 0;
}
--
2.14.0.rc0.dirty
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next prev parent reply other threads:[~2018-07-04 0:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 7:33 [PATCH] fscache: fix a kernel BUG at fs/fscache/operation.c:69! carmark.dlut
2018-05-08 13:43 ` Vegard Nossum
2018-06-15 17:49 ` Anthony DeRobertis
2018-07-04 0:10 ` NeilBrown [this message]
2018-07-04 9:14 ` [PATCH] cachefiles: fix multiple-put race David Howells
2018-07-04 12:29 ` [PATCH] cachefiles: Fix assertion "6 == 5 is false" at fs/fscache/operation.c:494 David Howells
2018-07-04 13:30 ` David Howells
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