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From:   Pavel Begunkov <asml.silence@gmail.com>
To:     Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] io_uring: fix extra put in sync_file_range()
Date:   Fri,  1 May 2020 17:09:36 +0300
Message-Id: <bd2ca136bb6bebe2b1bb94afc4fae464df151a84.1588341674.git.asml.silence@gmail.com>
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[   40.179474] refcount_t: underflow; use-after-free.
[   40.179499] WARNING: CPU: 6 PID: 1848 at lib/refcount.c:28 refcount_warn_saturate+0xae/0xf0
...
[   40.179612] RIP: 0010:refcount_warn_saturate+0xae/0xf0
[   40.179617] Code: 28 44 0a 01 01 e8 d7 01 c2 ff 0f 0b 5d c3 80 3d 15 44 0a 01 00 75 91 48 c7 c7 b8 f5 75 be c6 05 05 44 0a 01 01 e8 b7 01 c2 ff <0f> 0b 5d c3 80 3d f3 43 0a 01 00 0f 85 6d ff ff ff 48 c7 c7 10 f6
[   40.179619] RSP: 0018:ffffb252423ebe18 EFLAGS: 00010286
[   40.179623] RAX: 0000000000000000 RBX: ffff98d65e929400 RCX: 0000000000000000
[   40.179625] RDX: 0000000000000001 RSI: 0000000000000086 RDI: 00000000ffffffff
[   40.179627] RBP: ffffb252423ebe18 R08: 0000000000000001 R09: 000000000000055d
[   40.179629] R10: 0000000000000c8c R11: 0000000000000001 R12: 0000000000000000
[   40.179631] R13: ffff98d68c434400 R14: ffff98d6a9cbaa20 R15: ffff98d6a609ccb8
[   40.179634] FS:  0000000000000000(0000) GS:ffff98d6af580000(0000) knlGS:0000000000000000
[   40.179636] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   40.179638] CR2: 00000000033e3194 CR3: 000000006480a003 CR4: 00000000003606e0
[   40.179641] Call Trace:
[   40.179652]  io_put_req+0x36/0x40
[   40.179657]  io_free_work+0x15/0x20
[   40.179661]  io_worker_handle_work+0x2f5/0x480
[   40.179667]  io_wqe_worker+0x2a9/0x360
[   40.179674]  ? _raw_spin_unlock_irqrestore+0x24/0x40
[   40.179681]  kthread+0x12c/0x170
[   40.179685]  ? io_worker_handle_work+0x480/0x480
[   40.179690]  ? kthread_park+0x90/0x90
[   40.179695]  ret_from_fork+0x35/0x40
[   40.179702] ---[ end trace 85027405f00110aa ]---

Opcode handler must never put submission ref, but that's what
io_sync_file_range_finish() do. use io_steal_work() there.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 75ff4cc9818b..e7d7e83e3d56 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3515,7 +3515,7 @@ static void io_sync_file_range_finish(struct io_wq_work **workptr)
 	if (io_req_cancelled(req))
 		return;
 	__io_sync_file_range(req);
-	io_put_req(req); /* put submission ref */
+	io_steal_work(req, workptr);
 }
 
 static int io_sync_file_range(struct io_kiocb *req, bool force_nonblock)
-- 
2.24.0