[Gruzzberry]

What

fcntl with F_GETLK, F_SETLK, F_SETLKW and the old F_OGETLK, F_OSETLK, F_OSETLKW read the guest struct flock with a raw memcpy. A guest passing an invalid non-null pointer (for example 0x10) crashed the host emulator with an access violation. FreeBSD 11.4's sys_fcntl copies the structure in before kern_fcntl looks at the descriptor, so these commands fail with EFAULT for an unreadable pointer, ahead of EBADF and the other checks. The structure is now read with GuestCopyIn_nid_no_patch (24 bytes for the old commands, 32 for the new ones), and the virtual-directory EINVAL check moved after it. The F_GETLK result copy-out already failed with EFAULT and is unchanged.

Tested

Windows 11 (10.0.26200), WinLibs MinGW-w64 GCC 15.2.0 r7, Ninja, Release, -DBUILD_TESTING=ON, on current main.

• guest_kernel_fcntl: new checks pass 0x10 to all six lock commands on a regular file and to SetLock on descriptor -1, expecting EFAULT. On main the test crashes with a segmentation fault; with this change it passes, three runs out of three.
• Full suite: no failure touches this change. pr_overlap_encoding, agc_host_import_cut_lifetime and agc_driver_depth_plane_partial_store did not fail here. The failures are vulkan_validation_gate_reports and check_compile_test_windows_gcc_response_text_mode_is_not_reinterpreted (the WindowsApps python environment) and the two main_sync_renames_test_*_rename_with_detection_disabled tests (a non-ASCII file name assertion in a git script, 3 of 3 failing alone, not present in the earlier baseline).
• python tools/check_conventions.py --base upstream/main: passes.
• Not tested: Linux and macOS, a console, a title run.
• Not fixed, same on main and here: on non-Windows hosts F_GETLK into readable but read-only guest memory is not caught by the result copy-out.

Overlaps

• feat(libkernel): keep the SIGIO owner of a pipe for F_GETOWN and F_SETOWN #9557 and feat(libkernel): answer tcgetpgrp and tcsetpgrp on a pipe with its SIGIO owner #9566 change lines near RecordLock in DescriptorControl.cpp (feat(libkernel): answer tcgetpgrp and tcsetpgrp on a pipe with its SIGIO owner #9566 touches the virtual-directory check line this PR moves). Both are older, so they go first and this PR rebases.
• tools/pr_overlap.py could not compare DescriptorControl.cpp against feat(libkernel): report open, read and close notes on watched files #7121, feat(libkernel_sys): implement pwrite through the shared POSIX provider #9019, feat(libkernel): cancel blocked POSIX reads with owned operations #12682, fix(libkernel): preserve blocking sockets over nonblocking native transport #12688, feat(libkernel): cancel blocked POSIX writes with partial progress #12700 and feat(libkernel): support deferred cancellation in POSIX accept #12965, which conflict with main themselves. Their diffs do not touch RecordLock.

Checklist

• Based on current main; no other open PR implements the same function
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); no silent stubs added
• No notes, investigation .md files or images added to the repository
• New third-party code is a submodule built from source: none added
• Generic behaviour, not specific to one title
• Depends on: feat(libkernel): keep the SIGIO owner of a pipe for F_GETOWN and F_SETOWN #9557, feat(libkernel): answer tcgetpgrp and tcsetpgrp on a pipe with its SIGIO owner #9566; merge order: after feat(libkernel): keep the SIGIO owner of a pipe for F_GETOWN and F_SETOWN #9557, feat(libkernel): answer tcgetpgrp and tcsetpgrp on a pipe with its SIGIO owner #9566 (neighbouring lines)
• Fixes: none
• Unblocks: none
• GPUs tested: n/a
• AI-assisted: yes

AI-assisted (Claude Code).

🤖 Generated with Claude Code

[BunnyFl]

This matches FreeBSD 11.4's sys_fcntl, which does copyin of the struct flock (and the old struct __oflock) before kern_fcntl looks at the descriptor. So EFAULT now comes before the virtual-directory EINVAL and before a bad descriptor, as the new -1 case pins.

Build and test on Windows (WinLibs GCC, BUILD_TESTING=ON), PR merged into current main:

• guest_kernel_fcntl passes.
• With main's DescriptorControl.cpp restored, it segfaults on the new 0x10 cases.

[github-actions]

Some comparisons could not be completed because a pull request conflicts with the base branch. Review these shared files manually before concluding that there is no overlap.

Pull request	Shared files not compared
PR 7121	core/libs/prx/libkernel/File/src/DescriptorControl.cpp
PR 9019	core/libs/prx/libkernel/File/src/DescriptorControl.cpp
PR 12682	core/libs/prx/libkernel/File/src/DescriptorControl.cpp
PR 12688	core/libs/prx/libkernel/File/src/DescriptorControl.cpp
PR 12700	core/libs/prx/libkernel/File/src/DescriptorControl.cpp
PR 12965	core/libs/prx/libkernel/File/src/DescriptorControl.cpp

[ahmadmuj]

Checked head 97da73eed49dac518ee6e06a8e2df7cd6771cb39, PR base 92d2fdc3438f83e39d624eb65f3195bf2701568c on Linux/WSL. Built the actual libkernel/libc modules; guest_kernel_fcntl passes.

A separate protected-page probe passes all 24 cases: 23/24/31/32 readable bytes, all six lock commands, descriptor -1. It checks exact -1 returns and guest EFAULT/EBADF, including the 24-byte old and 32-byte current cutoffs. This matches the copy-before-descriptor order in FreeBSD.

Forcing the old size to 32 breaks six cases; restoring raw memcpy crashes twelve. After restoring the source, all 24 pass again. The same probe crashes in twelve cases on main 0fbe14c15361c420c65bc22cf2c3dc14cbda81d1.

Looks good to me for input copying. This does not test result copyout, host locking, or console behavior.