The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 85f0173df35e5462d89947135a6a5599c6c3ef6f Mon Sep 17 00:00:00 2001 From: Ziyang Xuan william.xuanziyang@huawei.com Date: Thu, 28 Jul 2022 09:33:07 +0800 Subject: [PATCH] ipv6/addrconf: fix a null-ptr-deref bug for ip6_ptr

Change net device's MTU to smaller than IPV6_MIN_MTU or unregister device while matching route. That may trigger null-ptr-deref bug for ip6_ptr probability as following.

========================================================= BUG: KASAN: null-ptr-deref in find_match.part.0+0x70/0x134 Read of size 4 at addr 0000000000000308 by task ping6/263

CPU: 2 PID: 263 Comm: ping6 Not tainted 5.19.0-rc7+ #14 Call trace: dump_backtrace+0x1a8/0x230 show_stack+0x20/0x70 dump_stack_lvl+0x68/0x84 print_report+0xc4/0x120 kasan_report+0x84/0x120 __asan_load4+0x94/0xd0 find_match.part.0+0x70/0x134 __find_rr_leaf+0x408/0x470 fib6_table_lookup+0x264/0x540 ip6_pol_route+0xf4/0x260 ip6_pol_route_output+0x58/0x70 fib6_rule_lookup+0x1a8/0x330 ip6_route_output_flags_noref+0xd8/0x1a0 ip6_route_output_flags+0x58/0x160 ip6_dst_lookup_tail+0x5b4/0x85c ip6_dst_lookup_flow+0x98/0x120 rawv6_sendmsg+0x49c/0xc70 inet_sendmsg+0x68/0x94

Reproducer as following: Firstly, prepare conditions: $ip netns add ns1 $ip netns add ns2 $ip link add veth1 type veth peer name veth2 $ip link set veth1 netns ns1 $ip link set veth2 netns ns2 $ip netns exec ns1 ip -6 addr add 2001:0db8:0:f101::1/64 dev veth1 $ip netns exec ns2 ip -6 addr add 2001:0db8:0:f101::2/64 dev veth2 $ip netns exec ns1 ifconfig veth1 up $ip netns exec ns2 ifconfig veth2 up $ip netns exec ns1 ip -6 route add 2000::/64 dev veth1 metric 1 $ip netns exec ns2 ip -6 route add 2001::/64 dev veth2 metric 1

Secondly, execute the following two commands in two ssh windows respectively: $ip netns exec ns1 sh $while true; do ip -6 addr add 2001:0db8:0:f101::1/64 dev veth1; ip -6 route add 2000::/64 dev veth1 metric 1; ping6 2000::2; done

$ip netns exec ns1 sh $while true; do ip link set veth1 mtu 1000; ip link set veth1 mtu 1500; sleep 5; done

It is because ip6_ptr has been assigned to NULL in addrconf_ifdown() firstly, then ip6_ignore_linkdown() accesses ip6_ptr directly without NULL check.

cpu0 cpu1 fib6_table_lookup __find_rr_leaf addrconf_notify [ NETDEV_CHANGEMTU ] addrconf_ifdown RCU_INIT_POINTER(dev->ip6_ptr, NULL) find_match ip6_ignore_linkdown

So we can add NULL check for ip6_ptr before using in ip6_ignore_linkdown() to fix the null-ptr-deref bug.

Fixes: dcd1f572954f ("net/ipv6: Remove fib6_idev") Signed-off-by: Ziyang Xuan william.xuanziyang@huawei.com Reviewed-by: David Ahern dsahern@kernel.org Link: https://lore.kernel.org/r/20220728013307.656257-1-william.xuanziyang@huawei.... Signed-off-by: Jakub Kicinski kuba@kernel.org

diff --git a/include/net/addrconf.h b/include/net/addrconf.h index f7506f08e505..c04f359655b8 100644 --- a/include/net/addrconf.h +++ b/include/net/addrconf.h @@ -405,6 +405,9 @@ static inline bool ip6_ignore_linkdown(const struct net_device *dev) { const struct inet6_dev *idev = __in6_dev_get(dev);

+ if (unlikely(!idev)) + return true; + return !!idev->cnf.ignore_routes_with_linkdown; }