CVE-2024-26951

In the Linux kernel, the following vulnerability has been resolved:

wireguard: netlink: check for dangling peer via is_dead instead of empty list

If all peers are removed via wg_peer_remove_all(), rather than setting
peer_list to empty, the peer is added to a temporary list with a head on
the stack of wg_peer_remove_all(). If a netlink dump is resumed and the
cursored peer is one that has been removed via wg_peer_remove_all(), it
will iterate from that peer and then attempt to dump freed peers.

Fix this by instead checking peer->is_dead, which was explictly created
for this purpose. Also move up the device_update_lock lockdep assertion,
since reading is_dead relies on that.

It can be reproduced by a small script like:

echo "Setting config..."
ip link add dev wg0 type wireguard
wg setconf wg0 /big-config
(
        while true; do
                echo "Showing config..."
                wg showconf wg0 > /dev/null
        done
) &
sleep 4
wg setconf wg0 <(printf "[Peer]\nPublicKey=$(wg genkey)\n")

Resulting in:

BUG: KASAN: slab-use-after-free in __lock_acquire+0x182a/0x1b20
Read of size 8 at addr ffff88811956ec70 by task wg/59
CPU: 2 PID: 59 Comm: wg Not tainted 6.8.0-rc2-debug+ #5
Call Trace:
 <TASK>
 dump_stack_lvl+0x47/0x70
 print_address_description.constprop.0+0x2c/0x380
 print_report+0xab/0x250
 kasan_report+0xba/0xf0
 __lock_acquire+0x182a/0x1b20
 lock_acquire+0x191/0x4b0
 down_read+0x80/0x440
 get_peer+0x140/0xcb0
 wg_get_device_dump+0x471/0x1130