* [PATCH] vfs: check i_count under lock in evict_inodes
@ 2016-07-12 0:15 Chunwei Chen
2016-07-12 0:46 ` Al Viro
0 siblings, 1 reply; 5+ messages in thread
From: Chunwei Chen @ 2016-07-12 0:15 UTC (permalink / raw)
To: linux-kernel; +Cc: Chunwei Chen, Alexander Viro, linux-fsdevel, stable
We need to check i_count again with i_lock held, because iput might re-add
i_count when lazytime is on. Without this check, we could end up with
double-free or use-after-free.
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
---
fs/inode.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/inode.c b/fs/inode.c
index 4ccbc21..10bb020 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -607,7 +607,12 @@ again:
continue;
spin_lock(&inode->i_lock);
- if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
+ /*
+ * check i_count again with lock, because iput might re-add
+ * it when lazytime is on.
+ */
+ if (atomic_read(&inode->i_count) ||
+ (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE))) {
spin_unlock(&inode->i_lock);
continue;
}
--
2.7.4
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] vfs: check i_count under lock in evict_inodes
2016-07-12 0:15 [PATCH] vfs: check i_count under lock in evict_inodes Chunwei Chen
@ 2016-07-12 0:46 ` Al Viro
2016-07-12 1:31 ` David Chen
0 siblings, 1 reply; 5+ messages in thread
From: Al Viro @ 2016-07-12 0:46 UTC (permalink / raw)
To: Chunwei Chen; +Cc: linux-kernel, linux-fsdevel, stable
On Mon, Jul 11, 2016 at 05:15:04PM -0700, Chunwei Chen wrote:
> We need to check i_count again with i_lock held, because iput might re-add
> i_count when lazytime is on. Without this check, we could end up with
> double-free or use-after-free.
Details, please. Ideally - with a reproducer. Who is calling that iput()
at that point of generic_shutdown_super() (has to be another thread) and
just what will happen if the same iput() is delayed until *after*
evict_inodes(), all the way into ->put_super(). At which point there's
no promise whatsoever that the data structures used by ->evict_inode()
hadn't been already freed...
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] vfs: check i_count under lock in evict_inodes
2016-07-12 0:46 ` Al Viro
@ 2016-07-12 1:31 ` David Chen
2016-07-12 1:40 ` Christoph Hellwig
2016-07-12 5:26 ` Al Viro
0 siblings, 2 replies; 5+ messages in thread
From: David Chen @ 2016-07-12 1:31 UTC (permalink / raw)
To: Al Viro; +Cc: lkml, linux-fsdevel, stable
Hi Al,
I'm not sure about the in-tree fs, but in zfsonlinux, it would offload
iput to a thread, so this would happen there. And it would wait for
the thread in put_super(), so that part is not a problem...
Thanks
2016-07-11 17:46 GMT-07:00 Al Viro <viro@zeniv.linux.org.uk>:
> On Mon, Jul 11, 2016 at 05:15:04PM -0700, Chunwei Chen wrote:
>> We need to check i_count again with i_lock held, because iput might re-add
>> i_count when lazytime is on. Without this check, we could end up with
>> double-free or use-after-free.
>
> Details, please. Ideally - with a reproducer. Who is calling that iput()
> at that point of generic_shutdown_super() (has to be another thread) and
> just what will happen if the same iput() is delayed until *after*
> evict_inodes(), all the way into ->put_super(). At which point there's
> no promise whatsoever that the data structures used by ->evict_inode()
> hadn't been already freed...
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] vfs: check i_count under lock in evict_inodes
2016-07-12 1:31 ` David Chen
@ 2016-07-12 1:40 ` Christoph Hellwig
2016-07-12 5:26 ` Al Viro
1 sibling, 0 replies; 5+ messages in thread
From: Christoph Hellwig @ 2016-07-12 1:40 UTC (permalink / raw)
To: David Chen; +Cc: Al Viro, lkml, linux-fsdevel, stable
On Mon, Jul 11, 2016 at 06:31:57PM -0700, David Chen wrote:
> Hi Al,
>
> I'm not sure about the in-tree fs, but in zfsonlinux, it would offload
> iput to a thread, so this would happen there. And it would wait for
> the thread in put_super(), so that part is not a problem...
And why exactly is your use of a broken and undistributable out of tree
module our problem?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] vfs: check i_count under lock in evict_inodes
2016-07-12 1:31 ` David Chen
2016-07-12 1:40 ` Christoph Hellwig
@ 2016-07-12 5:26 ` Al Viro
1 sibling, 0 replies; 5+ messages in thread
From: Al Viro @ 2016-07-12 5:26 UTC (permalink / raw)
To: David Chen; +Cc: lkml, linux-fsdevel, stable
On Mon, Jul 11, 2016 at 06:31:57PM -0700, David Chen wrote:
> Hi Al,
>
> I'm not sure about the in-tree fs, but in zfsonlinux, it would offload
> iput to a thread, so this would happen there. And it would wait for
> the thread in put_super(), so that part is not a problem...
*shrug* I hadn't looked (and won't look) at zfs glue, but I'd suggest
trying something along the line of stopping that thread in the beginning
of your ->kill_sb() (having told the sucker to stop offloading, of course)
and only then calling generic_shutdown_super()...
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-07-12 0:15 [PATCH] vfs: check i_count under lock in evict_inodes Chunwei Chen
2016-07-12 0:46 ` Al Viro
2016-07-12 1:31 ` David Chen
2016-07-12 1:40 ` Christoph Hellwig
2016-07-12 5:26 ` Al Viro
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