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qcow: better limits on cluster size

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Add a lower limit because cases such as eight byte clusters aren't
practical and aren't worth handling, tracking a cluster costs 16 bytes.

Also put an upper limit on the cluster size, choose 21 bits to match
qemu.

Change-Id: Ifcab081d0e630b5d26b0eafa552bd7c695821686
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1651458
Reviewed-by: Zach Reizner <zachr@chromium.org>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
(cherry picked from crosvm commit cae80e321acdccb1591124f6bf657758f1e75d1d)
Signed-off-by: Rob Bradford <robert.bradford@intel.com>
This commit is contained in:
Dylan Reid 2019-06-08 18:54:24 -07:00 committed by Samuel Ortiz
parent 0c9547618a
commit f927d1a2d7
1 changed files with 5 additions and 6 deletions
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11
qcow/src/qcow.rs
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@ -112,7 +112,10 @@ pub enum ImageType {
const QCOW_MAGIC: u32 = 0x5146_49fb;
// Default to a cluster size of 2^DEFAULT_CLUSTER_BITS
const DEFAULT_CLUSTER_BITS: u32 = 16;
const MAX_CLUSTER_BITS: u32 = 30;
// Limit clusters to reasonable sizes. Choose the same limits as qemu. Making the clusters smaller
// increases the amount of overhead for book keeping.
const MIN_CLUSTER_BITS: u32 = 9;
const MAX_CLUSTER_BITS: u32 = 21;
// Only support 2 byte refcounts, 2^refcount_order bits.
const DEFAULT_REFCOUNT_ORDER: u32 = 4;
@ -369,14 +372,10 @@ impl QcowFile {
}
let cluster_bits: u32 = header.cluster_bits;
if cluster_bits > MAX_CLUSTER_BITS {
if cluster_bits < MIN_CLUSTER_BITS || cluster_bits > MAX_CLUSTER_BITS {
return Err(Error::InvalidClusterSize);
}
let cluster_size = 0x01u64 << cluster_bits;
if cluster_size < size_of::<u64>() as u64 {
// Can't fit an offset in a cluster, nothing is going to work.
return Err(Error::InvalidClusterSize);
}
// No current support for backing files.
if header.backing_file_offset != 0 {