KASAN: invalid-access Write in enqueue_timer
Jason A. Donenfeld
Jason at zx2c4.com
Tue Feb 16 12:46:34 EST 2021
On Tue, Feb 16, 2021 at 6:28 PM Catalin Marinas <catalin.marinas at arm.com> wrote:
> Adding Jason and Ard. It may be a use-after-free in the wireguard
Thanks for sending this my way. Note: to my knowledge, Ard doesn't
work on wireguard.
> > hlist_add_head include/linux/list.h:883 [inline]
> > enqueue_timer+0x18/0xc0 kernel/time/timer.c:581
> > mod_timer+0x14/0x20 kernel/time/timer.c:1106
> > mod_peer_timer drivers/net/wireguard/timers.c:37 [inline]
> > wg_timers_any_authenticated_packet_traversal+0x68/0x90 drivers/net/wireguard/timers.c:215
The line of hlist_add_head that it's hitting is:
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
struct hlist_node *first = h->first;
So that means it's the dereferencing of h that's a problem. That comes from:
static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
unsigned int idx, unsigned long bucket_expiry)
hlist_add_head(&timer->entry, base->vectors + idx);
That means it concerns base->vectors + idx, not the timer_list object
that wireguard manages. That's confusing. Could that imply that the
bug is in freeing a previous timer without removing it from the timer
lists, so that it winds up being in base->vectors?
The allocation and deallocation backtrace is confusing
> > alloc_netdev_mqs+0x5c/0x3bc net/core/dev.c:10546
> > rtnl_create_link+0xc8/0x2b0 net/core/rtnetlink.c:3171
> > __rtnl_newlink+0x5bc/0x800 net/core/rtnetlink.c:3433
This suggests it's part of the `ip link add wg0 type wireguard` nelink
call, during it's allocation of the netdevice's private area. For
this, the wg_device struct is used. It has no timer_list structures in
> > netdev_freemem+0x18/0x2c net/core/dev.c:10500
> > netdev_release+0x30/0x44 net/core/net-sysfs.c:1828
> > device_release+0x34/0x90 drivers/base/core.c:1980
That smells like `ip link del wg0 type wireguard`. But again,
wg_device doesn't have any timer_lists in it.
So what's happening here exactly? I'm not really sure yet...
It'd be nice to have a reproducer.
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