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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Muhammad Sammar <muhammads@mellanox.com>,
        Feras Daoud <ferasda@mellanox.com>,
        Leon Romanovsky <leonro@mellanox.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.14 070/239] IB/ipoib: Ensure that MTU isnt less than minimum permitted
Date:   Tue, 19 Nov 2019 06:17:50 +0100
Message-Id: <20191119051313.031606081@linuxfoundation.org>
In-Reply-To: <20191119051255.850204959@linuxfoundation.org>
References: <20191119051255.850204959@linuxfoundation.org>
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From: Muhammad Sammar <muhammads@mellanox.com>

[ Upstream commit 142a9c287613560edf5a03c8d142c8b6ebc1995b ]

It is illegal to change MTU to a value lower than the minimum MTU
stated in ethernet spec. In addition to that we need to add 4 bytes
for encapsulation header (IPOIB_ENCAP_LEN).

Before "ifconfig ib0 mtu 0" command, succeeds while it obviously shouldn't.

Signed-off-by: Muhammad Sammar <muhammads@mellanox.com>
Reviewed-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/infiniband/ulp/ipoib/ipoib_main.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
index 1a93d3d58c8a4..caae4bfab950d 100644
--- a/drivers/infiniband/ulp/ipoib/ipoib_main.c
+++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
@@ -249,7 +249,8 @@ static int ipoib_change_mtu(struct net_device *dev, int new_mtu)
 		return 0;
 	}
 
-	if (new_mtu > IPOIB_UD_MTU(priv->max_ib_mtu))
+	if (new_mtu < (ETH_MIN_MTU + IPOIB_ENCAP_LEN) ||
+	    new_mtu > IPOIB_UD_MTU(priv->max_ib_mtu))
 		return -EINVAL;
 
 	priv->admin_mtu = new_mtu;
-- 
2.20.1