Subject: [PATCH v2] atm/fore200e: Fix possible data race in fore200e_open()

From: Gui-Dong Han <[email-masked]>
Date: Wed, 22 Jan 2025 02:37:45 +0000

Protect access to fore200e->available_cell_rate with rate_mtx lock to
prevent potential data race.

In this case, since the update depends on a prior read, a data race
could lead to a wrong fore200e.available_cell_rate value.

The field fore200e.available_cell_rate is generally protected by the lock
fore200e.rate_mtx when accessed. In all other read and write cases, this
field is consistently protected by the lock, except for this case and
during initialization.

This potential bug was detected by our experimental static analysis tool,
which analyzes locking APIs and paired functions to identify data races
and atomicity violations.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: [email-masked]
Signed-off-by: Gui-Dong Han <[email-masked]>
---
v2:
* Added a description of the data race hazard in fore200e_open(), as
suggested by Jakub Kicinski and Simon Horman.
---
 drivers/atm/fore200e.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/atm/fore200e.c b/drivers/atm/fore200e.c
index 4fea1149e003..f62e38571440 100644
--- a/drivers/atm/fore200e.c
+++ b/drivers/atm/fore200e.c
@@ -1374,7 +1374,9 @@ fore200e_open(struct atm_vcc *vcc)
 
 	vcc->dev_data = NULL;
 
+	mutex_lock(&fore200e->rate_mtx);
 	fore200e->available_cell_rate += vcc->qos.txtp.max_pcr;
+	mutex_unlock(&fore200e->rate_mtx);
 
 	kfree(fore200e_vcc);
 	return -EINVAL;
-- 
2.25.1