From: Michal Svoboda <pht@spatium.org>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [Bug 1054180] [NEW] DNS activity in slirp (user networking) mode quickly depletes file descriptors and crashes qemu
Date: Fri, 21 Sep 2012 16:13:23 -0000 [thread overview]
Message-ID: <20120921161324.22633.34633.malonedeb@chaenomeles.canonical.com> (raw)
In-Reply-To: 20120921161324.22633.34633.malonedeb@chaenomeles.canonical.com
Public bug reported:
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.
** Affects: qemu
Importance: Undecided
Status: New
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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:
New
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.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1054180/+subscriptions
next parent reply other threads:[~2012-09-21 16:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-21 16:13 Michal Svoboda [this message]
2017-08-21 7:47 ` [Qemu-devel] [Bug 1054180] Re: DNS activity in slirp (user networking) mode quickly depletes file descriptors and crashes qemu Thomas Huth
2017-08-21 7:48 ` Thomas Huth
2017-10-21 4:17 ` Launchpad Bug Tracker
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