Messages in this thread | | | From | Rainer Weikusat <> | Subject | Re: [PATCH] unix: avoid use-after-free in ep_remove_wait_queue (w/ Fixes:) | Date | Tue, 17 Nov 2015 21:37:46 +0000 |
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David Miller <davem@davemloft.net> writes: > From: Rainer Weikusat <rweikusat@mobileactivedefense.com> > Date: Mon, 16 Nov 2015 22:28:40 +0000 > >> 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.
[...]
>> Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com> >> Fixes: ec0d215f9420 ("af_unix: fix 'poll for write'/connected DGRAM sockets") > > So because of a corner case of epoll handling and sender socket release, > every single datagram sendmsg has to do a double lock now? > > I do not dispute the correctness of your fix at this point, but that > added cost in the fast path is really too high.
This leaves only the option of a somewhat incorrect solution and what is or isn't acceptable in this respect is somewhat difficult to decide. The basic options would be
- return EAGAIN even if sending became possible (Jason's most recent suggestions)
- retry sending a limited number of times, eg, once, before returning EAGAIN, on the grounds that this is nicer to the application and that redoing all the stuff up to the _lock in dgram_sendmsg can possibly/ likely be avoided
Which one do you prefer?
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