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authorChristian Krinitsin <mail@krinitsin.com>2025-06-30 12:24:58 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-06-30 12:27:06 +0000
commit33606b41d35115f887ea688b1a16f2ff85bf2fe4 (patch)
tree406b2c7b19a087ba437c68f3dbf0b589fa1d6150 /results/scraper/launchpad-without-comments/1054180
parentadedf8771bc4de3113041ca21bd4d0d1c0014b6a (diff)
downloadqemu-analysis-33606b41d35115f887ea688b1a16f2ff85bf2fe4.tar.gz
qemu-analysis-33606b41d35115f887ea688b1a16f2ff85bf2fe4.zip
add launchpad bug reports without comments
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+DNS activity in slirp (user networking) mode quickly depletes file descriptors and crashes qemu
+
+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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