linux-kernel - [PATCH] atm: zatm: Fix potential Spectre v1

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Message-ID: <20180629182807.GA26287@embeddedor.com>
Date:   Fri, 29 Jun 2018 13:28:07 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Chas Williams <3chas3@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-atm-general@...ts.sourceforge.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] atm: zatm: Fix potential Spectre v1

pool can be indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

drivers/atm/zatm.c:1491 zatm_ioctl() warn: potential spectre issue
'zatm_dev->pool_info' (local cap)

Fix this by sanitizing pool before using it to index
zatm_dev->pool_info

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@...r.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/atm/zatm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/atm/zatm.c b/drivers/atm/zatm.c
index a8d2eb0..2c288d1 100644
--- a/drivers/atm/zatm.c
+++ b/drivers/atm/zatm.c
@@ -1483,6 +1483,8 @@ static int zatm_ioctl(struct atm_dev *dev,unsigned int cmd,void __user *arg)
 					return -EFAULT;
 				if (pool < 0 || pool > ZATM_LAST_POOL)
 					return -EINVAL;
+				pool = array_index_nospec(pool,
+							  ZATM_LAST_POOL + 1);
 				if (copy_from_user(&info,
 				    &((struct zatm_pool_req __user *) arg)->info,
 				    sizeof(info))) return -EFAULT;
-- 
2.7.4