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Miller" , Hideaki YOSHIFUJI , David Ahern , Jakub Kicinski , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, sharathv@codeaurora.org, chinagar@codeaurora.org Subject: [PATCH] ipv6: Honor route mtu if it is within limit of dev mtu Date: Mon, 22 Feb 2021 22:02:35 +0530 Message-Id: <1614011555-21951-1-git-send-email-kapandey@codeaurora.org> X-Mailer: git-send-email 2.7.4 To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" When netdevice MTU is increased via sysfs, NETDEV_CHANGEMTU is raised. addrconf_notify -> rt6_mtu_change -> rt6_mtu_change_route -> fib6_nh_mtu_change As part of handling NETDEV_CHANGEMTU notification we land up on a condition where if route mtu is less than dev mtu and route mtu equals ipv6_devconf mtu, route mtu gets updated. Due to this v6 traffic end up using wrong MTU then configured earlier. This commit fixes this by removing comparison with ipv6_devconf and updating route mtu only when it is greater than incoming dev mtu. This can be easily reproduced with below script: pre-condition: device up(mtu =3D 1500) and route mtu for both v4 and v6 is 1500 test-script: ip route change 192.168.0.0/24 dev eth0 src 192.168.0.1 mtu 1400 ip -6 route change 2001::/64 dev eth0 metric 256 mtu 1400 echo 1400 > /sys/class/net/eth0/mtu ip route change 192.168.0.0/24 dev eth0 src 192.168.0.1 mtu 1500 echo 1500 > /sys/class/net/eth0/mtu Signed-off-by: Kaustubh Pandey --- net/ipv6/route.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 1536f49..653b6c7 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -4813,8 +4813,7 @@ static int fib6_nh_mtu_change(struct fib6_nh *nh, voi= d *_arg) struct inet6_dev *idev =3D __in6_dev_get(arg->dev); u32 mtu =3D f6i->fib6_pmtu; =20 - if (mtu >=3D arg->mtu || - (mtu < arg->mtu && mtu =3D=3D idev->cnf.mtu6)) + if (mtu >=3D arg->mtu) fib6_metric_set(f6i, RTAX_MTU, arg->mtu); =20 spin_lock_bh(&rt6_exception_lock); --=20 2.7.4