path: root/net/hsr/hsr_device.c
diff options
authorRainer Weikusat <rweikusat@mobileactivedefense.com>2015-11-20 22:07:23 +0000
committerDavid S. Miller <davem@davemloft.net>2015-11-23 12:29:58 -0500
commit7d267278a9ece963d77eefec61630223fce08c6c (patch)
tree307652e3130a7a5d9537ac1d53f98754af8bb0a0 /net/hsr/hsr_device.c
parentcgroups: Allow dynamically changing net_classid (diff)
unix: avoid use-after-free in ep_remove_wait_queue
Rainer Weikusat <rweikusat@mobileactivedefense.com> writes: An AF_UNIX datagram socket being the client in an n:1 association with some server socket is only allowed to send messages to the server if the receive queue of this socket contains at most sk_max_ack_backlog datagrams. This implies that prospective writers might be forced to go to sleep despite none of the message presently enqueued on the server receive queue were sent by them. In order to ensure that these will be woken up once space becomes again available, the present unix_dgram_poll routine does a second sock_poll_wait call with the peer_wait wait queue of the server socket as queue argument (unix_dgram_recvmsg does a wake up on this queue after a datagram was received). This is inherently problematic because the server socket is only guaranteed to remain alive for as long as the client still holds a reference to it. In case the connection is dissolved via connect or by the dead peer detection logic in unix_dgram_sendmsg, the server socket may be freed despite "the polling mechanism" (in particular, epoll) still has a pointer to the corresponding peer_wait queue. There's no way to forcibly deregister a wait queue with epoll. Based on an idea by Jason Baron, the patch below changes the code such that a wait_queue_t belonging to the client socket is enqueued on the peer_wait queue of the server whenever the peer receive queue full condition is detected by either a sendmsg or a poll. A wake up on the peer queue is then relayed to the ordinary wait queue of the client socket via wake function. The connection to the peer wait queue is again dissolved if either a wake up is about to be relayed or the client socket reconnects or a dead peer is detected or the client socket is itself closed. This enables removing the second sock_poll_wait from unix_dgram_poll, thus avoiding the use-after-free, while still ensuring that no blocked writer sleeps forever. Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com> Fixes: ec0d215f9420 ("af_unix: fix 'poll for write'/connected DGRAM sockets") Reviewed-by: Jason Baron <jbaron@akamai.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/hsr/hsr_device.c')
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