Remove precondition on result of IOCTL_VM_SOCKETS_GET_LOCAL_CID

[simonjbeaumont]

Motivation:

When using the IOCTL_VM_SOCKETS_GET_LOCAL_CID call to get the local Context ID for a VSOCK socket, we precondition that the resulting Context ID is not VMADDR_CID_ANY. This probably was an assumption too far and we've seen an issue¹ where this led to a crash in the tests.

Digging a little more on this and it looks like we've been too strict:

• Based on the tests in XNU it looks like it expects the result of this call to not be VMADDR_CID_ANY².
• The HyperV transport in the Linux kernel always returns VMADDR_CID_ANY³.
• Loopback transport always returns VMADDR_CID_LOCAL⁴.
• Virtio transport seems to return VMADDR_CID_ANY in the error path⁵.
• The VMCI transport sends a control message datagram to the host⁶.

All that to say... we probably shouldn't make any precondition on the result of IOCTL_VM_SOCKETS_GET_LOCAL_CID since it appears to tightly coupled to the VSOCK transport, and I don't think we can confidently say anything about what the value should be.

Additionally, while investigating this I found that the tests actually crash when we don't have /dev/vsock available, which was an oversight:

❯ docker run --privileged --rm -v $PWD:/code -w /code -it swift:5.9.1-jammy ls /dev/vsock
/dev/vsock

❯ docker run --privileged --rm -v $PWD:/code -w /code -it swift:5.9.1-jammy swift test --filter VsockAddressTest.testGetLocalCID
Building for debugging...
Build complete! (6.90s)
Test Suite 'Selected tests' started at 2023-11-06 13:18:07.422
Test Suite 'VsockAddressTest' started at 2023-11-06 13:18:07.424
Test Case 'VsockAddressTest.testGetLocalCID' started at 2023-11-06 13:18:07.424
Test Case 'VsockAddressTest.testGetLocalCID' passed (0.004 seconds)
Test Suite 'VsockAddressTest' passed at 2023-11-06 13:18:07.427
         Executed 1 test, with 0 failures (0 unexpected) in 0.004 (0.004) seconds
Test Suite 'Selected tests' passed at 2023-11-06 13:18:07.427
         Executed 1 test, with 0 failures (0 unexpected) in 0.004 (0.004) seconds

❯ docker run --rm -v $PWD:/code -w /code -it swift:5.9.1-jammy ls /dev/vsock
ls: cannot access '/dev/vsock': No such file or directory

❯ docker run --rm -v $PWD:/code -w /code -it swift:5.9.1-jammy swift test --filter VsockAddressTest.testGetLocalCID
Building for debugging...
Build complete! (6.90s)
Test Suite 'Selected tests' started at 2023-11-06 13:18:43.133
Test Suite 'VsockAddressTest' started at 2023-11-06 13:18:43.134
Test Case 'VsockAddressTest.testGetLocalCID' started at 2023-11-06 13:18:43.134
NIOPosix/VsockAddress.swift:223: Fatal error: 'try!' expression unexpectedly raised an error: open(file:oFlag:): No such file or directory (errno: 2)
...[crash dump]...

These tests should be skipped by virtue of try XCTSkipUnless(System.supportsVsock), which checks that we can create a socket with AF_VSOCK. However, on Linux, this is not enough of a guard and we should probably also check for the presence of /dev/vsock.

Modifications:

1. Remove the precondition that checks that the local CID as returned by the ioctl() is not VMADDR_CID_ANY.
2. Don't force-try to open /dev/vsock, instead let this fail, which will propagate up to through the Channel.getOption path.
3. Update the hasVsockSupport guard that conditionally runs the test to include checking for the presence of /dev/vsock when on Linux.

Result:

The tests no longer crash when /dev/vsock is not available on Linux. Note that we don't currently exercise these tests in CI because the CI runner doesn't have a new enough Linux kernel, but I've included some logs below from some manual runs.

Linux, with /dev/vsock (still runs and passes)

❯ docker run --privileged --rm -v $PWD:/code -w /code -it swift:5.9.0-jammy swift test --filter VsockAddressTest.testGetLocalCID
...
Test Suite 'Selected tests' started at 2023-11-07 18:11:09.259
Test Suite 'VsockAddressTest' started at 2023-11-07 18:11:09.262
Test Case 'VsockAddressTest.testGetLocalCID' started at 2023-11-07 18:11:09.262
Test Case 'VsockAddressTest.testGetLocalCID' passed (0.004 seconds)
Test Suite 'VsockAddressTest' passed at 2023-11-07 18:11:09.266
         Executed 1 test, with 0 failures (0 unexpected) in 0.004 (0.004) seconds
Test Suite 'Selected tests' passed at 2023-11-07 18:11:09.266
         Executed 1 test, with 0 failures (0 unexpected) in 0.004 (0.004) seconds

Linux, without /dev/vsock (skips, no longer crashes)

❯ docker run --rm -v $PWD:/code -w /code -it swift:5.9.0-jammy swift test --filter VsockAddressTest.testGetLocalCID
Test Suite 'Selected tests' started at 2023-11-07 18:12:00.285
Test Suite 'VsockAddressTest' started at 2023-11-07 18:12:00.287
Test Case 'VsockAddressTest.testGetLocalCID' started at 2023-11-07 18:12:00.287
/code/Tests/NIOPosixTests/VsockAddressTest.swift:57: VsockAddressTest.testGetLocalCID : Test skipped: required false value but got true
Test Case 'VsockAddressTest.testGetLocalCID' skipped (0.002 seconds)
Test Suite 'VsockAddressTest' passed at 2023-11-07 18:12:00.289
         Executed 1 test, with 1 test skipped and 0 failures (0 unexpected) in 0.002 (0.002) seconds
Test Suite 'Selected tests' passed at 2023-11-07 18:12:00.289
         Executed 1 test, with 1 test skipped and 0 failures (0 unexpected) in 0.002 (0.002) seconds

macOS (skips, as before)

❯ uname
Darwin

❯ swift test --filter VsockAddressTest.testGetLocalCID
Test Suite 'Selected tests' started at 2023-11-07 18:14:46.468.
Test Suite 'swift-nioPackageTests.xctest' started at 2023-11-07 18:14:46.469.
Test Suite 'VsockAddressTest' started at 2023-11-07 18:14:46.469.
Test Case '-[NIOPosixTests.VsockAddressTest testGetLocalCID]' started.
/Users/Si/work/code/swift-nio/Tests/NIOPosixTests/VsockAddressTest.swift:57: -[NIOPosixTests.VsockAddressTest testGetLocalCID] : Test skipped
Test Case '-[NIOPosixTests.VsockAddressTest testGetLocalCID]' skipped (0.001 seconds).
Test Suite 'VsockAddressTest' passed at 2023-11-07 18:14:46.471.
         Executed 1 test, with 1 test skipped and 0 failures (0 unexpected) in 0.001 (0.001) seconds
Test Suite 'swift-nioPackageTests.xctest' passed at 2023-11-07 18:14:46.471.
         Executed 1 test, with 1 test skipped and 0 failures (0 unexpected) in 0.001 (0.001) seconds
Test Suite 'Selected tests' passed at 2023-11-07 18:14:46.471.
         Executed 1 test, with 1 test skipped and 0 failures (0 unexpected) in 0.001 (0.002) seconds

Related issues

• Resolves VsockAddressTest.testGetLocalCID crashes in jammy with Swift 5.9.1 #2585.

Footnotes

1. VsockAddressTest.testGetLocalCID crashes in jammy with Swift 5.9.1 #2585 ↩

2. https://opensource.apple.com/source/xnu/xnu-7195.50.7.100.1/tests/vsock.c.auto.html ↩

3. https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/net/vmw_vsock/hyperv_transport.c#L437-L440 ↩

4. https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/net/vmw_vsock/vsock_loopback.c#L24-L27 ↩

5. https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/net/vmw_vsock/virtio_transport.c#L79-L95 ↩

6. https://github.com/torvalds/linux/blob/d2f51b3516dade79269ff45eae2a7668ae711b25/drivers/misc/vmw_vmci/vmci_guest.c#L88-L100 ↩

[FranzBusch]

Nice catches and thanks for the detailed explanation. Those changes make sense to me!