[PATCH 4.19 110/114] gtp: fix an use-after-free in ipv4_pdp_find()

From: Greg Kroah-Hartman
Date: Thu Jan 02 2020 - 17:23:36 EST

From: Taehee Yoo <ap420073@xxxxxxxxx>

[ Upstream commit 94dc550a5062030569d4aa76e10e50c8fc001930 ]

ipv4_pdp_find() is called in TX packet path of GTP.
ipv4_pdp_find() internally uses gtp->tid_hash to lookup pdp context.
In the current code, gtp->tid_hash and gtp->addr_hash are freed by
->dellink(), which is gtp_dellink().
But gtp_dellink() would be called while packets are processing.
So, gtp_dellink() should not free gtp->tid_hash and gtp->addr_hash.
Instead, dev->priv_destructor() would be used because this callback
is called after all packet processing safely.

Test commands:
ip link add veth1 type veth peer name veth2
ip a a 172.0.0.1/24 dev veth1
ip link set veth1 up
ip a a 172.99.0.1/32 dev lo

gtp-link add gtp1 &

gtp-tunnel add gtp1 v1 200 100 172.99.0.2 172.0.0.2
ip r a 172.99.0.2/32 dev gtp1
ip link set gtp1 mtu 1500

ip netns add ns2
ip link set veth2 netns ns2
ip netns exec ns2 ip a a 172.0.0.2/24 dev veth2
ip netns exec ns2 ip link set veth2 up
ip netns exec ns2 ip a a 172.99.0.2/32 dev lo
ip netns exec ns2 ip link set lo up

ip netns exec ns2 gtp-link add gtp2 &
ip netns exec ns2 gtp-tunnel add gtp2 v1 100 200 172.99.0.1 172.0.0.1
ip netns exec ns2 ip r a 172.99.0.1/32 dev gtp2
ip netns exec ns2 ip link set gtp2 mtu 1500

hping3 172.99.0.2 -2 --flood &
ip link del gtp1

Splat looks like:
[ 72.568081][ T1195] BUG: KASAN: use-after-free in ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.568916][ T1195] Read of size 8 at addr ffff8880b9a35d28 by task hping3/1195
[ 72.569631][ T1195]
[ 72.569861][ T1195] CPU: 2 PID: 1195 Comm: hping3 Not tainted 5.5.0-rc1 #199
[ 72.570547][ T1195] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 72.571438][ T1195] Call Trace:
[ 72.571764][ T1195] dump_stack+0x96/0xdb
[ 72.572171][ T1195] ? ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.572761][ T1195] print_address_description.constprop.5+0x1be/0x360
[ 72.573400][ T1195] ? ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.573971][ T1195] ? ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.574544][ T1195] __kasan_report+0x12a/0x16f
[ 72.575014][ T1195] ? ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.575593][ T1195] kasan_report+0xe/0x20
[ 72.576004][ T1195] ipv4_pdp_find.isra.12+0x130/0x170 [gtp]
[ 72.576577][ T1195] gtp_build_skb_ip4+0x199/0x1420 [gtp]
[ ... ]
[ 72.647671][ T1195] BUG: unable to handle page fault for address: ffff8880b9a35d28
[ 72.648512][ T1195] #PF: supervisor read access in kernel mode
[ 72.649158][ T1195] #PF: error_code(0x0000) - not-present page
[ 72.649849][ T1195] PGD a6c01067 P4D a6c01067 PUD 11fb07067 PMD 11f939067 PTE 800fffff465ca060
[ 72.652958][ T1195] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
[ 72.653834][ T1195] CPU: 2 PID: 1195 Comm: hping3 Tainted: G B 5.5.0-rc1 #199
[ 72.668062][ T1195] RIP: 0010:ipv4_pdp_find.isra.12+0x86/0x170 [gtp]
[ ... ]
[ 72.679168][ T1195] Call Trace:
[ 72.679603][ T1195] gtp_build_skb_ip4+0x199/0x1420 [gtp]
[ 72.681915][ T1195] ? ipv4_pdp_find.isra.12+0x170/0x170 [gtp]
[ 72.682513][ T1195] ? lock_acquire+0x164/0x3b0
[ 72.682966][ T1195] ? gtp_dev_xmit+0x35e/0x890 [gtp]
[ 72.683481][ T1195] gtp_dev_xmit+0x3c2/0x890 [gtp]
[ ... ]

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Signed-off-by: Taehee Yoo <ap420073@xxxxxxxxx>
Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/net/gtp.c | 34 +++++++++++++++++-----------------
1 file changed, 17 insertions(+), 17 deletions(-)

--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -644,9 +644,16 @@ static void gtp_link_setup(struct net_de
}

static int gtp_hashtable_new(struct gtp_dev *gtp, int hsize);
-static void gtp_hashtable_free(struct gtp_dev *gtp);
static int gtp_encap_enable(struct gtp_dev *gtp, struct nlattr *data[]);

+static void gtp_destructor(struct net_device *dev)
+{
+ struct gtp_dev *gtp = netdev_priv(dev);
+
+ kfree(gtp->addr_hash);
+ kfree(gtp->tid_hash);
+}
+
static int gtp_newlink(struct net *src_net, struct net_device *dev,
struct nlattr *tb[], struct nlattr *data[],
struct netlink_ext_ack *extack)
@@ -681,13 +688,15 @@ static int gtp_newlink(struct net *src_n

gn = net_generic(dev_net(dev), gtp_net_id);
list_add_rcu(&gtp->list, &gn->gtp_dev_list);
+ dev->priv_destructor = gtp_destructor;

netdev_dbg(dev, "registered new GTP interface\n");

return 0;

out_hashtable:
- gtp_hashtable_free(gtp);
+ kfree(gtp->addr_hash);
+ kfree(gtp->tid_hash);
out_encap:
gtp_encap_disable(gtp);
return err;
@@ -696,9 +705,14 @@ out_encap:
static void gtp_dellink(struct net_device *dev, struct list_head *head)
{
struct gtp_dev *gtp = netdev_priv(dev);
+ struct pdp_ctx *pctx;
+ int i;
+
+ for (i = 0; i < gtp->hash_size; i++)
+ hlist_for_each_entry_rcu(pctx, &gtp->tid_hash[i], hlist_tid)
+ pdp_context_delete(pctx);

gtp_encap_disable(gtp);
- gtp_hashtable_free(gtp);
list_del_rcu(&gtp->list);
unregister_netdevice_queue(dev, head);
}
@@ -776,20 +790,6 @@ err1:
return -ENOMEM;
}

-static void gtp_hashtable_free(struct gtp_dev *gtp)
-{
- struct pdp_ctx *pctx;
- int i;
-
- for (i = 0; i < gtp->hash_size; i++)
- hlist_for_each_entry_rcu(pctx, &gtp->tid_hash[i], hlist_tid)
- pdp_context_delete(pctx);
-
- synchronize_rcu();
- kfree(gtp->addr_hash);
- kfree(gtp->tid_hash);
-}
-
static struct sock *gtp_encap_enable_socket(int fd, int type,
struct gtp_dev *gtp)
{