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Subject[PATCH 4.19 007/134] ipv6: make ip6_create_rt_rcu return ip6_null_entry instead of NULL
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Xin Long <lucien.xin@gmail.com>

[ Upstream commit 1c87e79a002f6a159396138cd3f3ab554a2a8887 ]

Jianlin reported a crash:

[ 381.484332] BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
[ 381.619802] RIP: 0010:fib6_rule_lookup+0xa3/0x160
[ 382.009615] Call Trace:
[ 382.020762] <IRQ>
[ 382.030174] ip6_route_redirect.isra.52+0xc9/0xf0
[ 382.050984] ip6_redirect+0xb6/0xf0
[ 382.066731] icmpv6_notify+0xca/0x190
[ 382.083185] ndisc_redirect_rcv+0x10f/0x160
[ 382.102569] ndisc_rcv+0xfb/0x100
[ 382.117725] icmpv6_rcv+0x3f2/0x520
[ 382.133637] ip6_input_finish+0xbf/0x460
[ 382.151634] ip6_input+0x3b/0xb0
[ 382.166097] ipv6_rcv+0x378/0x4e0

It was caused by the lookup function __ip6_route_redirect() returns NULL in
fib6_rule_lookup() when ip6_create_rt_rcu() returns NULL.

So we fix it by simply making ip6_create_rt_rcu() return ip6_null_entry
instead of NULL.

v1->v2:
- move down 'fallback:' to make it more readable.

Fixes: e873e4b9cc7e ("ipv6: use fib6_info_hold_safe() when necessary")
Reported-by: Jianlin Shi <jishi@redhat.com>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/route.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1048,14 +1048,20 @@ static struct rt6_info *ip6_create_rt_rc
struct rt6_info *nrt;

if (!fib6_info_hold_safe(rt))
- return NULL;
+ goto fallback;

nrt = ip6_dst_alloc(dev_net(dev), dev, flags);
- if (nrt)
- ip6_rt_copy_init(nrt, rt);
- else
+ if (!nrt) {
fib6_info_release(rt);
+ goto fallback;
+ }
+
+ ip6_rt_copy_init(nrt, rt);
+ return nrt;

+fallback:
+ nrt = dev_net(dev)->ipv6.ip6_null_entry;
+ dst_hold(&nrt->dst);
return nrt;
}

@@ -1104,10 +1110,6 @@ restart:
dst_hold(&rt->dst);
} else {
rt = ip6_create_rt_rcu(f6i);
- if (!rt) {
- rt = net->ipv6.ip6_null_entry;
- dst_hold(&rt->dst);
- }
}

rcu_read_unlock();

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