5.4-stable review patch. If anyone has any objections, please let me know.
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From: xu xin xu.xin16@zte.com.cn
commit bb487272380d120295e955ad8acfcbb281b57642 upstream.
Problem ========= After commit 67f695134703 ("ipv6: Move setting default metric for routes"), we noticed that the logic of assigning the default value of fc_metirc changed in the ioctl process. That is, when users use ioctl(fd, SIOCADDRT, rt) with a non-zero metric to add a route, then they may fail to delete a route with passing in a metric value of 0 to the kernel by ioctl(fd, SIOCDELRT, rt). But iproute can succeed in deleting it.
As a reference, when using iproute tools by netlink to delete routes with a metric parameter equals 0, like the command as follows:
ip -6 route del fe80::/64 via fe81::5054:ff:fe11:3451 dev eth0 metric 0
the user can still succeed in deleting the route entry with the smallest metric.
Root Reason =========== After commit 67f695134703 ("ipv6: Move setting default metric for routes"), When ioctl() pass in SIOCDELRT with a zero metric, rtmsg_to_fib6_config() will set a defalut value (1024) to cfg->fc_metric in kernel, and in ip6_route_del() and the line 4074 at net/ipv3/route.c, it will check by
if (cfg->fc_metric && cfg->fc_metric != rt->fib6_metric) continue;
and the condition is true and skip the later procedure (deleting route) because cfg->fc_metric != rt->fib6_metric. But before that commit, cfg->fc_metric is still zero there, so the condition is false and it will do the following procedure (deleting).
Solution ======== In order to keep a consistent behaviour across netlink() and ioctl(), we should allow to delete a route with a metric value of 0. So we only do the default setting of fc_metric in route adding.
CC: stable@vger.kernel.org # 5.4+ Fixes: 67f695134703 ("ipv6: Move setting default metric for routes") Co-developed-by: Fan Yu fan.yu9@zte.com.cn Signed-off-by: Fan Yu fan.yu9@zte.com.cn Signed-off-by: xu xin xu.xin16@zte.com.cn Reviewed-by: David Ahern dsahern@kernel.org Link: https://lore.kernel.org/r/20240514201102055dD2Ba45qKbLlUMxu_DTHP@zte.com.cn Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/route.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -4341,7 +4341,7 @@ static void rtmsg_to_fib6_config(struct .fc_table = l3mdev_fib_table_by_index(net, rtmsg->rtmsg_ifindex) ? : RT6_TABLE_MAIN, .fc_ifindex = rtmsg->rtmsg_ifindex, - .fc_metric = rtmsg->rtmsg_metric ? : IP6_RT_PRIO_USER, + .fc_metric = rtmsg->rtmsg_metric, .fc_expires = rtmsg->rtmsg_info, .fc_dst_len = rtmsg->rtmsg_dst_len, .fc_src_len = rtmsg->rtmsg_src_len, @@ -4377,6 +4377,9 @@ int ipv6_route_ioctl(struct net *net, un rtnl_lock(); switch (cmd) { case SIOCADDRT: + /* Only do the default setting of fc_metric in route adding */ + if (cfg.fc_metric == 0) + cfg.fc_metric = IP6_RT_PRIO_USER; err = ip6_route_add(&cfg, GFP_KERNEL, NULL); break; case SIOCDELRT: