diff options
author | Jason Baron <jbaron@akamai.com> | 2018-08-03 17:24:53 -0400 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2018-08-03 16:44:19 -0700 |
commit | 51f7e95187f127d5eadf50541943813ff57f12ba (patch) | |
tree | bc23c743b9cf6bed86cd611cdc16e31b4bb4fb70 /net/unix/af_unix.c | |
parent | a394b3af206c211b80b02e47c19aab763fd33b3d (diff) |
af_unix: ensure POLLOUT on remote close() for connected dgram socket
Applications use -ECONNREFUSED as returned from write() in order to
determine that a socket should be closed. However, when using connected
dgram unix sockets in a poll/write loop, a final POLLOUT event can be
missed when the remote end closes. Thus, the poll is stuck forever:
thread 1 (client) thread 2 (server)
connect() to server
write() returns -EAGAIN
unix_dgram_poll()
-> unix_recvq_full() is true
close()
->unix_release_sock()
->wake_up_interruptible_all()
unix_dgram_poll() (due to the
wake_up_interruptible_all)
-> unix_recvq_full() still is true
->free all skbs
Now thread 1 is stuck and will not receive anymore wakeups. In this
case, when thread 1 gets the -EAGAIN, it has not queued any skbs
otherwise the 'free all skbs' step would in fact cause a wakeup and
a POLLOUT return. So the race here is probably fairly rare because
it means there are no skbs that thread 1 queued and that thread 1
schedules before the 'free all skbs' step.
This issue was reported as a hang when /dev/log is closed.
The fix is to signal POLLOUT if the socket is marked as SOCK_DEAD, which
means a subsequent write() will get -ECONNREFUSED.
Reported-by: Ian Lance Taylor <iant@golang.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/unix/af_unix.c')
-rw-r--r-- | net/unix/af_unix.c | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index 1772a0e32665..d1edfa3cad61 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -430,7 +430,12 @@ static int unix_dgram_peer_wake_me(struct sock *sk, struct sock *other) connected = unix_dgram_peer_wake_connect(sk, other); - if (unix_recvq_full(other)) + /* If other is SOCK_DEAD, we want to make sure we signal + * POLLOUT, such that a subsequent write() can get a + * -ECONNREFUSED. Otherwise, if we haven't queued any skbs + * to other and its full, we will hang waiting for POLLOUT. + */ + if (unix_recvq_full(other) && !sock_flag(other, SOCK_DEAD)) return 1; if (connected) |