net_mana: Added validation for ContiguousBufferMemory construction

vm/devices/net/net_mana/src/lib.rs

@@ -1492,6 +1492,15 @@ struct OutOfMemory;
 
 impl ContiguousBufferManager {
     pub fn new(dma_client: Arc<dyn DmaClient>, page_limit: u32) -> anyhow::Result<Self> {
+        anyhow::ensure!(
+            page_limit.is_power_of_two(),
+            anyhow::anyhow!("page_limit must be a power of two, {page_limit} is not.")
+        );
+        anyhow::ensure!(
+            PAGE_SIZE64 * Into::<u64>::into(page_limit) <= Into::<u64>::into(u32::MAX),
+            anyhow::anyhow!("{page_limit} will overflow the len field")
+        );
+
         let len = PAGE_SIZE32 * page_limit;
         let mem = dma_client.allocate_dma_buffer(len as usize)?;
         Ok(Self {
@@ -1526,3 +1535,33 @@ impl Inspect for ContiguousBufferManager {
             .counter("failed_allocations", self.failed_allocations);
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use anyhow::{Result, anyhow, ensure};
+    use user_driver_emulated_mock::DeviceTestMemory;
+
+    #[test]
+    fn page_counts_powers_of_two_only() -> Result<()> {
+        for i in 1..35 {
+            let dtm = DeviceTestMemory::new(Into::<u64>::into(i) * 2, false, "test");
+            match ContiguousBufferManager::new(dtm.dma_client(), i) {
+                Ok(_) => {
+                    ensure!(
+                        i.is_power_of_two(),
+                        anyhow!("The CBM should only work for powers of 2")
+                    );
+                }
+                Err(_) => {
+                    ensure!(
+                        !i.is_power_of_two(),
+                        anyhow!("Powers of 2 should get CBMs, failed for {i} pages.")
+                    );
+                }
+            }
+        }
+
+        Ok(())
+    }
+}