** Also affects: ubuntu
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1687653
Title:
QEMU-KVM / detect_zeroes causes KVM to start unlimited number of
threads on Guest-Sided High-IO with big Blocksize
Status in QEMU:
Confirmed
Status in Ubuntu:
New
Bug description:
QEMU-KVM in combination with "detect_zeroes=on" makes a Guest able to
DoS the Host. This is possible if the Host itself has "detect_zeroes"
enabled and the Guest writes a large Chunk of data with a huge
blocksize onto the drive.
E.g.: dd if=/dev/zero of=/tmp/DoS bs=1G count=1 oflag=direct
All QEMU-Versions after implementation of detect_zeroes are affected.
Prior are unaffected. This is absolutely critical, please fix this
ASAP!
#####
Provided by Dominik Csapak:
source , bs , count , O_DIRECT, behaviour
urandom , bs 1M, count 1024, O_DIRECT: OK
file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1M, count 1024, O_DIRECT: OK
zero file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1G, count 1, O_DIRECT: NOT OK
zero file , bs 1G, count 1, O_DIRECT: NOT OK
zero file , bs 1G, count 1, no O_DIRECT: NOT OK
rand file , bs 1G, count 1, O_DIRECT: OK
rand file , bs 1G, count 1, no O_DIRECT: OK
discard on:
urandom , bs 1M, count 1024, O_DIRECT: OK
rand file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1M, count 1024, O_DIRECT: OK
zero file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1G, count 1, O_DIRECT: NOT OK
zero file , bs 1G, count 1, O_DIRECT: NOT OK
zero file , bs 1G, count 1, no O_DIRECT: NOT OK
rand file , bs 1G, count 1, O_DIRECT: OK
rand file , bs 1G, count 1, no O_DIRECT: OK
detect_zeros off:
urandom , bs 1M, count 1024, O_DIRECT: OK
rand file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1M, count 1024, O_DIRECT: OK
zero file , bs 1M, count 1024, O_DIRECT: OK
/dev/zero , bs 1G, count 1, O_DIRECT: OK
zero file , bs 1G, count 1, O_DIRECT: OK
zero file , bs 1G, count 1, no O_DIRECT: OK
rand file , bs 1G, count 1, O_DIRECT: OK
rand file , bs 1G, count 1, no O_DIRECT: OK
#####
Provided by Florian Strankowski
bs - count - io-threads
512K - 2048 - 2
1M - 1024 - 2
2M - 512 - 4
4M - 256 - 6
8M - 128 - 10
16M - 64 - 18
32M - 32 - uncountable
Please refer to further information here:
https://bugzilla.proxmox.com/show_bug.cgi?id=1368
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