linux-kernel - [PATCH] thunderbolt: Fix a double put in tb_cfg_read

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Date:   Mon, 22 Mar 2021 20:15:12 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     andreas.noever@...il.com, michael.jamet@...el.com,
        mika.westerberg@...ux.intel.com, YehezkelShB@...il.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH] thunderbolt: Fix a double put in tb_cfg_read_raw

In tb_cfg_read_raw, req is allocated by tb_cfg_request_alloc()
with an initial reference. Before calling tb_cfg_request_sync(),
there is no refcount inc operation. tb_cfg_request_sync()
calls tb_cfg_request(..,req,..) and if the callee failed,
the initial reference of req is dropped and req is freed.

Later in tb_cfg_read_raw before the err check,
tb_cfg_request_put(req) is called again. It may cause error
in race.

My patch puts tb_cfg_request_put(req) after the err check
finished to avoid unexpected result.

Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
---
 drivers/thunderbolt/ctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/thunderbolt/ctl.c b/drivers/thunderbolt/ctl.c
index f1aeaff9f368..bb60269c89ab 100644
--- a/drivers/thunderbolt/ctl.c
+++ b/drivers/thunderbolt/ctl.c
@@ -890,11 +890,11 @@ struct tb_cfg_result tb_cfg_read_raw(struct tb_ctl *ctl, void *buffer,

 		res = tb_cfg_request_sync(ctl, req, timeout_msec);

-		tb_cfg_request_put(req);
-
 		if (res.err != -ETIMEDOUT)
 			break;

+		tb_cfg_request_put(req);
+
 		/* Wait a bit (arbitrary time) until we send a retry */
 		usleep_range(10, 100);
 	}
-- 
2.25.1