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Message-ID: <e879112d-3285-d6d8-457b-2ae2f8d38aaf@gmail.com>
Date: Mon, 15 Jun 2020 09:02:27 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Taehee Yoo <ap420073@...il.com>, davem@...emloft.net,
kuba@...nel.org, netdev@...r.kernel.org
Cc: pshelar@...ira.com
Subject: Re: [PATCH net] ip_tunnel: fix use-after-free in ip_tunnel_lookup()
On 6/15/20 8:06 AM, Taehee Yoo wrote:
> In the datapath, the ip_tunnel_lookup() is used and it internally uses
> fallback tunnel device pointer, which is fb_tunnel_dev.
> This pointer is protected by RTNL. It's not enough to be used
> in the datapath.
> So, this pointer would be used after an interface is deleted.
> It eventually results in the use-after-free problem.
>
> In order to avoid the problem, the new tunnel pointer variable is added,
> which indicates a fallback tunnel device's tunnel pointer.
> This is protected by both RTNL and RCU.
> So, it's safe to be used in the datapath.
>
> Test commands:
> ip netns add A
> ip netns add B
> ip link add eth0 type veth peer name eth1
> ip link set eth0 netns A
> ip link set eth1 netns B
>
> ip netns exec A ip link set lo up
> ip netns exec A ip link set eth0 up
> ip netns exec A ip link add gre1 type gre local 10.0.0.1 \
> remote 10.0.0.2
> ip netns exec A ip link set gre1 up
> ip netns exec A ip a a 10.0.100.1/24 dev gre1
> ip netns exec A ip a a 10.0.0.1/24 dev eth0
>
> ip netns exec B ip link set lo up
> ip netns exec B ip link set eth1 up
> ip netns exec B ip link add gre1 type gre local 10.0.0.2 \
> remote 10.0.0.1
> ip netns exec B ip link set gre1 up
> ip netns exec B ip a a 10.0.100.2/24 dev gre1
> ip netns exec B ip a a 10.0.0.2/24 dev eth1
> ip netns exec A hping3 10.0.100.2 -2 --flood -d 60000 &
> ip netns del B
>
> Splat looks like:
> [ 133.319668][ C3] BUG: KASAN: use-after-free in ip_tunnel_lookup+0x9d6/0xde0
> [ 133.343852][ C3] Read of size 4 at addr ffff8880b1701c84 by task hping3/1222
> [ 133.344724][ C3]
> [ 133.345002][ C3] CPU: 3 PID: 1222 Comm: hping3 Not tainted 5.7.0+ #591
> [ 133.345814][ C3] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
> [ 133.373336][ C3] Call Trace:
> [ 133.374792][ C3] <IRQ>
> [ 133.375205][ C3] dump_stack+0x96/0xdb
> [ 133.375789][ C3] print_address_description.constprop.6+0x2cc/0x450
> [ 133.376720][ C3] ? ip_tunnel_lookup+0x9d6/0xde0
> [ 133.377431][ C3] ? ip_tunnel_lookup+0x9d6/0xde0
> [ 133.378130][ C3] ? ip_tunnel_lookup+0x9d6/0xde0
> [ 133.378851][ C3] kasan_report+0x154/0x190
> [ 133.379494][ C3] ? ip_tunnel_lookup+0x9d6/0xde0
> [ 133.380200][ C3] ip_tunnel_lookup+0x9d6/0xde0
> [ 133.380894][ C3] __ipgre_rcv+0x1ab/0xaa0 [ip_gre]
> [ 133.381630][ C3] ? rcu_read_lock_sched_held+0xc0/0xc0
> [ 133.382429][ C3] gre_rcv+0x304/0x1910 [ip_gre]
> [ ... ]
>
> Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
> Signed-off-by: Taehee Yoo <ap420073@...il.com>
> ---
> include/net/ip_tunnels.h | 1 +
> net/ipv4/ip_tunnel.c | 11 ++++++++---
> 2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h
> index 076e5d7db7d3..7442c517bb75 100644
> --- a/include/net/ip_tunnels.h
> +++ b/include/net/ip_tunnels.h
> @@ -164,6 +164,7 @@ struct ip_tunnel_net {
> struct rtnl_link_ops *rtnl_link_ops;
> struct hlist_head tunnels[IP_TNL_HASH_SIZE];
> struct ip_tunnel __rcu *collect_md_tun;
> + struct ip_tunnel __rcu *fb_tun;
> int type;
> };
>
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index f4f1d11eab50..285b863e2fcc 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -162,8 +162,9 @@ struct ip_tunnel *ip_tunnel_lookup(struct ip_tunnel_net *itn,
> if (t && t->dev->flags & IFF_UP)
> return t;
>
> - if (itn->fb_tunnel_dev && itn->fb_tunnel_dev->flags & IFF_UP)
> - return netdev_priv(itn->fb_tunnel_dev);
> + t = rcu_dereference(itn->fb_tun);
> + if (t && t->dev->flags & IFF_UP)
> + return t;
>
There is no need for a new variable.
Your patch does not add any new rcu grace period, so it seems obvious that you
relied on existing grace periods.
The real question is why ip_tunnel_uninit() does not clear itn->fb_tunnel_dev
And of course why ip_tunnel_lookup() does not a READ_ONCE()
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index f4f1d11eab502290f9d74e2c8aafd69bceb58763..2416aa33d3645e1da967ec4c914564c5727a4d80 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -87,6 +87,7 @@ struct ip_tunnel *ip_tunnel_lookup(struct ip_tunnel_net *itn,
{
unsigned int hash;
struct ip_tunnel *t, *cand = NULL;
+ struct net_device *ndev;
struct hlist_head *head;
hash = ip_tunnel_hash(key, remote);
@@ -162,8 +163,9 @@ struct ip_tunnel *ip_tunnel_lookup(struct ip_tunnel_net *itn,
if (t && t->dev->flags & IFF_UP)
return t;
- if (itn->fb_tunnel_dev && itn->fb_tunnel_dev->flags & IFF_UP)
- return netdev_priv(itn->fb_tunnel_dev);
+ ndev = READ_ONCE(itn->fb_tunnel_dev);
+ if (ndev && ndev->flags & IFF_UP)
+ return netdev_priv(ndev);
return NULL;
}
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