virtio: validate descriptor index from avail ring #2780
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Pull request overview
This PR hardens the virtio queue implementation against malicious or buggy guests by validating that descriptor indices read from the guest-provided avail ring are within the configured queue size, returning a specific error on violation.
Changes:
- Add a new
QueueError::InvalidDescriptorIndex(u16)error variant for invalid avail-ring descriptor indices. - Validate the descriptor index read from the avail ring against
queue_sizebefore using it.
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The descriptor index read from the guest's available ring was used directly without checking it against queue_size. A malicious or buggy guest could supply an out-of-range index. Add an explicit bounds check with a clear error message.
A queue_size of 0 causes division-by-zero panics in get_available_descriptor_index and set_used_descriptor, which both compute modulo queue_size. Reject it early in QueueCore::new.
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| #[error("descriptor index {0} is out of range")] | ||
| InvalidDescriptorIndex(u16), |
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The InvalidDescriptorIndex error message doesn’t include the queue size / valid range, which makes debugging guest issues harder. Consider including queue_size in the variant (e.g., store both the index and queue_size) and mention the valid range in the error text.
| mem: GuestMemory, | ||
| params: QueueParams, | ||
| ) -> Result<Self, QueueError> { | ||
| if params.size == 0 { |
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This new params.size == 0 check is redundant with QueueCoreGetWork::new’s is_power_of_two() validation (which already rejects 0), and it only checks for 0 (not other invalid sizes). To avoid inconsistent validation if SplitQueueGetWork::new is ever called directly, either remove this check (rely on the outer validation) or validate the full invariant here (non-zero power-of-two).
| if params.size == 0 { | |
| if !params.size.is_power_of_two() { |
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The descriptor index read from the guest's available ring was used directly without checking it against queue_size. A malicious or buggy guest could supply an out-of-range index. Add an explicit bounds check with a clear error message.