linux-kernel - [PATCH 5.15 148/179] ethtool: ioctl: fix potential NULL deref in ethtool_set

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Message-Id: <20211129181723.817662887@linuxfoundation.org>
Date:   Mon, 29 Nov 2021 19:19:02 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Yufeng Mo <moyufeng@...wei.com>,
        Huazhong Tan <tanhuazhong@...wei.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Julian Wiedmann <jwi@...ux.ibm.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 148/179] ethtool: ioctl: fix potential NULL deref in ethtool_set_coalesce()

From: Julian Wiedmann <jwi@...ux.ibm.com>

[ Upstream commit 0276af2176c78771da7f311621a25d7608045827 ]

ethtool_set_coalesce() now uses both the .get_coalesce() and
.set_coalesce() callbacks. But the check for their availability is
buggy, so changing the coalesce settings on a device where the driver
provides only _one_ of the callbacks results in a NULL pointer
dereference instead of an -EOPNOTSUPP.

Fix the condition so that the availability of both callbacks is
ensured. This also matches the netlink code.

Note that reproducing this requires some effort - it only affects the
legacy ioctl path, and needs a specific combination of driver options:
- have .get_coalesce() and .coalesce_supported but no
 .set_coalesce(), or
- have .set_coalesce() but no .get_coalesce(). Here eg. ethtool doesn't
  cause the crash as it first attempts to call ethtool_get_coalesce()
  and bails out on error.

Fixes: f3ccfda19319 ("ethtool: extend coalesce setting uAPI with CQE mode")
Cc: Yufeng Mo <moyufeng@...wei.com>
Cc: Huazhong Tan <tanhuazhong@...wei.com>
Cc: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>
Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
Link: https://lore.kernel.org/r/20211126175543.28000-1-jwi@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/ethtool/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index f2abc31528883..e4983f473a3c5 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -1697,7 +1697,7 @@ static noinline_for_stack int ethtool_set_coalesce(struct net_device *dev,
 	struct ethtool_coalesce coalesce;
 	int ret;
 
-	if (!dev->ethtool_ops->set_coalesce && !dev->ethtool_ops->get_coalesce)
+	if (!dev->ethtool_ops->set_coalesce || !dev->ethtool_ops->get_coalesce)
 		return -EOPNOTSUPP;
 
 	ret = dev->ethtool_ops->get_coalesce(dev, &coalesce, &kernel_coalesce,
-- 
2.33.0