net: Allow passing in a configured tap fd on the command line

Allow the process that spawned crosvm to pass in a configured tap file
descriptor for networking.  If this option is provided then crosvm will
ignore the other networking related command line flags (like mac
address, netmask, etc).

Passing in a configured tap device allows us to run crosvm without
having to give it CAP_NET_ADMIN.

BUG=none
TEST=Start a container and verify that networking still works

Change-Id: I70b9e6ae030d66c4882e4e48804dc2f29d9874ba
Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1081394
Reviewed-by: Zach Reizner <zachr@chromium.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/net_util/src/lib.rs b/net_util/src/lib.rs
index 273c1ca..0826729 100644
--- a/net_util/src/lib.rs
+++ b/net_util/src/lib.rs
@@ -449,6 +449,15 @@ impl AsRawFd for Tap {
     }
 }
 
+impl FromRawFd for Tap {
+    unsafe fn from_raw_fd(fd: RawFd) -> Tap {
+        Tap {
+            tap_file: File::from_raw_fd(fd),
+            if_name: [0; 16usize],
+        }
+    }
+}
+
 pub mod fakes {
     use super::*;
     use std::fs::OpenOptions;