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[Qemu-devel] [Bug 1054180] Re: DNS activity in slirp (user networking) m
From: |
Thomas Huth |
Subject: |
[Qemu-devel] [Bug 1054180] Re: DNS activity in slirp (user networking) mode quickly depletes file descriptors and crashes qemu |
Date: |
Mon, 21 Aug 2017 07:48:39 -0000 |
Also could you please provide the exact command line that you use to
start QEMU?
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https://bugs.launchpad.net/bugs/1054180
Title:
DNS activity in slirp (user networking) mode quickly depletes file
descriptors and crashes qemu
Status in QEMU:
Incomplete
Bug description:
Hi, we have encountered quite some trouble with filedescriptor
depletion of the qemu process. We have figured out that it can be
demonstrated easily by doing a lot of DNS queries inside the VM -- in
our real world scenario this is caused by running centos network
install with a fast mirror.
This situation is further problematic because qemu can't handle fd depletion
very well:
1) if ulimit is 1024 then qemu hangs in infinite loop whenever it tries to
open the 1025th fd
2) setting ulimit >1024 does not help that much because qemu uses select and
max. fd set size is 1024 per default => qemu crashes because of buffer overflow
in select()
3) setting ulimit > 1024 AND recompiling with large enough fd set size AND
disabling gcc's fortify source seems to work, but that's really just a hot-fix
The problem can be replicated quite easily by running something like
while :; do echo >/dev/udp/10.0.2.3/53; done
inside a Linux VM -- crash comes very soon.
This problem is present in current qemu (1.2.0) and in earlier as
well.
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