[patch 3/5] fs: fix bdi writeback use after free 1

npiggin
2009-09-15T19:25:51Z

[-- Attachment #1: fs-bdiwb-rcu-fix-2.patch --]
[-- Type: text/plain, Size: 1241 bytes --]

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
!on stack case, giving a false positive in this test and causing corruption.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
fs/fs-writeback.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c
+++ linux-2.6/fs/fs-writeback.c
@@ -114,6 +114,7 @@ static void bdi_work_free(struct rcu_hea
static void wb_work_complete(struct bdi_work *work)
{
const enum writeback_sync_modes sync_mode = work->sync_mode;
+ int onstack = bdi_work_on_stack(work);

/*
* For allocated work, we can clear the done/seen bit right here.
@@ -121,9 +122,9 @@ static void wb_work_complete(struct bdi_
* to after the RCU grace period, since the stack could be invalidated
* as soon as bdi_work_clear() has done the wakeup.
*/
- if (!bdi_work_on_stack(work))
+ if (!onstack)
bdi_work_clear(work);
- if (sync_mode == WB_SYNC_NONE || bdi_work_on_stack(work))
+ if (sync_mode == WB_SYNC_NONE || onstack)
call_rcu(&work->rcu_head, bdi_work_free);
}