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Subject[PATCH net] net: vlan: fix a UAF in vlan_dev_real_dev()
Date
The real_dev of a vlan net_device may be freed after
unregister_vlan_dev(). Access the real_dev continually by
vlan_dev_real_dev() will trigger the UAF problem for the
real_dev like following:

==================================================================
BUG: KASAN: use-after-free in vlan_dev_real_dev+0xf9/0x120
Call Trace:
kasan_report.cold+0x83/0xdf
vlan_dev_real_dev+0xf9/0x120
is_eth_port_of_netdev_filter.part.0+0xb1/0x2c0
is_eth_port_of_netdev_filter+0x28/0x40
ib_enum_roce_netdev+0x1a3/0x300
ib_enum_all_roce_netdevs+0xc7/0x140
netdevice_event_work_handler+0x9d/0x210
...

Freed by task 9288:
kasan_save_stack+0x1b/0x40
kasan_set_track+0x1c/0x30
kasan_set_free_info+0x20/0x30
__kasan_slab_free+0xfc/0x130
slab_free_freelist_hook+0xdd/0x240
kfree+0xe4/0x690
kvfree+0x42/0x50
device_release+0x9f/0x240
kobject_put+0x1c8/0x530
put_device+0x1b/0x30
free_netdev+0x370/0x540
ppp_destroy_interface+0x313/0x3d0
...

Set vlan->real_dev to NULL after dev_put(real_dev) in
unregister_vlan_dev(). Check real_dev is not NULL before
access it in vlan_dev_real_dev().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+e4df4e1389e28972e955@syzkaller.appspotmail.com
Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
---
net/8021q/vlan.c | 1 +
net/8021q/vlan_core.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 55275ef9a31a..1106da84e725 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -126,6 +126,7 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)

/* Get rid of the vlan's reference to real_dev */
dev_put(real_dev);
+ vlan->real_dev = NULL;
}

int vlan_check_real_dev(struct net_device *real_dev,
diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index 59bc13b5f14f..343f34479d8b 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -103,7 +103,7 @@ struct net_device *vlan_dev_real_dev(const struct net_device *dev)
{
struct net_device *ret = vlan_dev_priv(dev)->real_dev;

- while (is_vlan_dev(ret))
+ while (ret && is_vlan_dev(ret))
ret = vlan_dev_priv(ret)->real_dev;

return ret;
--
2.25.1
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