ovpn: fix peer refcount leak in TCP error paths
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observed exploitation
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In the Linux kernel, the following vulnerability has been resolved:
ovpn: fix peer refcount leak in TCP error paths
When either the TCP RX or TX error path calls ovpn_peer_hold() followed
by schedule_work(&peer->tcp.defer_del_work), and the work item is already
pending from the other path, schedule_work() returns false and the work
runs only once. Since ovpn_tcp_peer_del_work() calls ovpn_peer_put()
exactly once, the extra reference taken by the losing path is never
dropped, leaking the peer object.
The race window:
CPU0 (strparser/RX error): CPU1 (tcp_tx_work/TX error):
ovpn_peer_hold() <- refcnt+1 ovpn_peer_hold() <- refcnt+2
schedule_work() <- queued schedule_work() <- NO-OP
(work already pending)
ovpn_tcp_peer_del_work runs:
ovpn_peer_del()
ovpn_peer_put() <- refcnt+1
<- peer never freed
Fix by checking the return value of schedule_work() in both paths and
calling ovpn_peer_put() to drop the extra reference if the work was
already pending. ovpn_peer_hold() is kept unconditional in the TX path
as it cannot fail at that point.
Affected products
Linux · Linux