virtio-devices: balloon: Cap inflate and deflate descriptor length - #8177
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Drop inflate or deflate descriptors whose len exceeds the Linux driver maximum of VIRTIO_BALLOON_ARRAY_PFNS_MAX PFN entries of 4 bytes each. Without the cap, a guest can submit a descriptor with a huge len over a small backing and drive an unbounded warn loop in the device thread. Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
rbradford
approved these changes
May 8, 2026
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Hardening. The inflate and deflate queues carry a packed array of 32 bit Page Frame Number (PFN) entries. The spec puts no upper bound on
desc.len. Meaning, for example, a guest can submit a descriptor withdesc.len= 1 GiB over a small backing, and the device thread then walks 256M entries emitting one warn per unmapped PFN. This is a guest driven host log and worker DoS.Cap
desc.lenat the Linux driver maximum ofVIRTIO_BALLOON_ARRAY_PFNS_MAXPFN entries of 4 bytes each. No real driver hits the cap.