Add comprehensive overlayfs copy-up test suite to gVisor

[milantracy]

Description

Problem / Missing Coverage

Currently, gVisor's open-source test suite (test/syscalls / test/e2e) lacks comprehensive tests for overlayfs copy-up behaviors and edge cases. The only existing test is a basic container integration test (images/basic/integrationtest/test_copy_up.c) covering open(O_RDWR) and mmap on regular files.

Important edge cases in overlayfs copy-up are currently untested in the repository, including:

1. Non-copy-upable lower files (FIFOs / Sockets): Verifying that open(O_WRONLY) or access(..., W_OK) on lower-layer FIFOs/sockets that cannot be copied up fail cleanly with EPERM / EACCES rather than hanging or attempting invalid copy-up operations.
2. Copy-up triggers: Operations like truncate, chmod, chown, utimes, link, symlink, mknod, and mkdir on lower-layer dentries.
3. Permission checks: Ensuring read-only files (0444) on lower layers do not get copied up when O_RDWR open attempts fail with EACCES.
4. Special files on read-only mounts / overlayfs: Verifying that character devices (/dev/null) and pipes behave correctly across overlay layers and read-only mounts.

Proposed Solution

Add a dedicated CopyUpTest test suite to gVisor's test suite (under test/syscalls or test/e2e) to cover these overlayfs copy-up scenarios.

• Prevents regressions in overlayfs copy-up handling (e.g., deadlocks/hangs when opening lower FIFOs for write access or incorrect mount/copy-up permissions).
• Ensures consistent behavior between gVisor overlayfs implementation and native Linux kernel overlayfs.

Is this feature related to a specific bug?

No response

Do you have a specific solution in mind?

No response

[wpan36]

Hi! I’d like to work on this issue. I’m planning to start with tests for non-copy-upable lower FIFOs and Unix sockets, covering writable open() and access(W_OK) behavior.