descriptor_utils: check for size overflow in new()

Move the check for length overflow that was in available_bytes() into
Reader::new() and Writer::new().  This simplifies callers, since they
can assume that once a valid Reader or Writer has been constructed,
available_bytes() cannot fail.  Since we are walking the descriptor
chain during new() anyway, this extra check should be essentially free.

BUG=None
TEST=cargo test -p devices descriptor_utils

Change-Id: Ibeb1defd3728e7b71356650094b0885f3419ed47
Signed-off-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/1873142
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Stephen Barber <smbarber@chromium.org>

1 files changed, 1 insertions, 9 deletions

diff --git a/devices/src/virtio/balloon.rs b/devices/src/virtio/balloon.rs
index 4f2e692..460aba5 100644
--- a/devices/src/virtio/balloon.rs
+++ b/devices/src/virtio/balloon.rs
@@ -105,15 +105,7 @@ impl Worker {
                         continue;
                     }
                 };
-                let data_length = match reader.available_bytes() {
-                    Ok(l) => l,
-                    Err(e) => {
-                        error!("balloon: failed to get available bytes: {}", e);
-                        queue.add_used(&self.mem, index, 0);
-                        needs_interrupt = true;
-                        continue;
-                    }
-                };
+                let data_length = reader.available_bytes();
 
                 if data_length % 4 != 0 {
                     error!("invalid inflate buffer size: {}", data_length);