lkml.org 
[lkml]   [2022]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[net] ipv6/addrconf: fix a null-ptr-deref bug for ip6_ptr
Date
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
\
 
 \ /
  Last update: 2022-07-22 09:42    [W:0.223 / U:0.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site