The patch titled
Subject: writeback: fix use-after-free in finish_writeback_work()
has been added to the -mm tree. Its filename is
writeback-fix-use-after-free-in-finish_writeback_work.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/writeback-fix-use-after-free-in-finish_writeback_work.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/writeback-fix-use-after-free-in-finish_writeback_work.patch
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------------------------------------------------------
From: Tejun Heo <tj@xxxxxxxxxx>
Subject: writeback: fix use-after-free in finish_writeback_work()
finish_writeback_work() reads @done->waitq after decrementing @done->cnt.
However, once @done->cnt reaches zero, @done may be freed (from stack) at
any moment and @done->waitq can contain something unrelated by the time
finish_writeback_work() tries to read it. This led to the following
crash.
"BUG: kernel NULL pointer dereference, address: 0000000000000002"
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
CPU: 40 PID: 555153 Comm: kworker/u98:50 Kdump: loaded Not tainted
...
Workqueue: writeback wb_workfn (flush-btrfs-1)
RIP: 0010:_raw_spin_lock_irqsave+0x10/0x30
Code: 48 89 d8 5b c3 e8 50 db 6b ff eb f4 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53 9c 5b fa 31 c0 ba 01 00 00 00 <f0> 0f b1 17 75 05 48 89 d8 5b c3 89 c6 e8 fe ca 6b ff eb f2 66 90
RSP: 0018:ffffc90049b27d98 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000246 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000003 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffff889fff407600 R11: ffff88ba9395d740 R12: 000000000000e300
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88bfdfa00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 0000000002409005 CR4: 00000000001606e0
Call Trace:
__wake_up_common_lock+0x63/0xc0
wb_workfn+0xd2/0x3e0
process_one_work+0x1f5/0x3f0
worker_thread+0x2d/0x3d0
kthread+0x111/0x130
ret_from_fork+0x1f/0x30
Fix it by reading and caching @done->waitq before decrementing
@done->cnt.
Link: http://lkml.kernel.org/r/20190924010631.GH2233839@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 5b9cce4c7eb069 ("writeback: Generalize and expose wb_completion")
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Debugged-by: Chris Mason <clm@xxxxxx>
Reviewed-by: Jens Axboe <axboe@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.2+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/fs-writeback.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/fs/fs-writeback.c~writeback-fix-use-after-free-in-finish_writeback_work
+++ a/fs/fs-writeback.c
@@ -164,8 +164,13 @@ static void finish_writeback_work(struct
if (work->auto_free)
kfree(work);
- if (done && atomic_dec_and_test(&done->cnt))
- wake_up_all(done->waitq);
+ if (done) {
+ wait_queue_head_t *waitq = done->waitq;
+
+ /* @done can't be accessed after the following dec */
+ if (atomic_dec_and_test(&done->cnt))
+ wake_up_all(waitq);
+ }
}
static void wb_queue_work(struct bdi_writeback *wb,
_
Patches currently in -mm which might be from tj@xxxxxxxxxx are
writeback-fix-use-after-free-in-finish_writeback_work.patch
