Messages in this thread Patch in this message | | | From | Ziyang Xuan <> | Subject | [net] ipv6/addrconf: fix a null-ptr-deref bug for ip6_ptr | Date | Fri, 22 Jul 2022 15:41:53 +0800 |
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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.
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
And in order to increase the probability of reproduce, we can add mdelay() in find_match() as following:
static bool find_match(struct fib6_nh *nh, u32 fib6_flags, if (nh->fib_nh_flags & RTNH_F_DEAD) goto out;
+ mdelay(1000); if (ip6_ignore_linkdown(nh->fib_nh_dev) && nh->fib_nh_flags & RTNH_F_LINKDOWN && !(strict & RT6_LOOKUP_F_IGNORE_LINKSTATE))
========================================================= 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 sock_sendmsg+0x8c/0xb0
It is because ip6_ptr has been assigned to NULL in addrconf_ifdown(), and ip6_ignore_linkdown() in find_match() accesses ip6_ptr directly. Although find_match() routine is under rcu_read_lock(), but there is not synchronize_net() before assign NULL to make rcu grace period end.
So we can add synchronize_net() before assign ip6_ptr to NULL in addrconf_ifdown() to fix the null-ptr-deref bug.
Fixes: 8814c4b53381 ("[IPV6] ADDRCONF: Convert addrconf_lock to RCU.") Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com> --- net/ipv6/addrconf.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 49cc6587dd77..63d33b29ad21 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -3757,6 +3757,7 @@ static int addrconf_ifdown(struct net_device *dev, bool unregister) idev->dead = 1; /* protected by rtnl_lock */ + synchronize_net(); RCU_INIT_POINTER(dev->ip6_ptr, NULL); /* Step 1.5: remove snmp6 entry */ -- 2.25.1
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