Re: [patch 3/5] fs: fix bdi writeback use after free 1
From: Jens Axboe
Date: Tue Sep 15 2009 - 15:32:13 EST
On Wed, Sep 16 2009, npiggin@xxxxxxx wrote:
>
By the time bdi_work_on_stack gets evaluated again in bdi_work_free, it
>
cna already have been deallocated and used for something else in the
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!on stack case, giving a false positive in this test and causing corruption.
You are right, that is also buggy... Applied.
>
>
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
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---
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fs/fs-writeback.c | 5 +++--
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1 file changed, 3 insertions(+), 2 deletions(-)
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>
Index: linux-2.6/fs/fs-writeback.c
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===================================================================
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--- linux-2.6.orig/fs/fs-writeback.c
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+++ linux-2.6/fs/fs-writeback.c
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@@ -114,6 +114,7 @@ static void bdi_work_free(struct rcu_hea
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static void wb_work_complete(struct bdi_work *work)
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{
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const enum writeback_sync_modes sync_mode = work->sync_mode;
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+ int onstack = bdi_work_on_stack(work);
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>
/*
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* For allocated work, we can clear the done/seen bit right here.
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@@ -121,9 +122,9 @@ static void wb_work_complete(struct bdi_
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* to after the RCU grace period, since the stack could be invalidated
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* as soon as bdi_work_clear() has done the wakeup.
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*/
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- if (!bdi_work_on_stack(work))
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+ if (!onstack)
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bdi_work_clear(work);
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- if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
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+ if (sync_mode == WB_SYNC_NONE || onstack)
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call_rcu(&work->rcu_head, bdi_work_free);
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}
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>
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--
Jens Axboe
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