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ladybird/Kernel/Syscalls/disown.cpp

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Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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/*
* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
*
Everything: Move to SPDX license identifiers in all files. SPDX License Identifiers are a more compact / standardized way of representing file license information. See: https://spdx.dev/resources/use/#identifiers This was done with the `ambr` search and replace tool. ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
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* SPDX-License-Identifier: BSD-2-Clause
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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*/
Kernel: Move all tasks-related code to the Tasks subdirectory
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#include <Kernel/Tasks/Process.h>
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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namespace Kernel {
Kernel: Replace KResult and KResultOr<T> with Error and ErrorOr<T> We now use AK::Error and AK::ErrorOr<T> in both kernel and userspace! This was a slightly tedious refactoring that took a long time, so it's not unlikely that some bugs crept in. Nevertheless, it does pass basic functionality testing, and it's just real nice to finally see the same pattern in all contexts. :^)
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ErrorOr<FlatPtr> Process::sys$disown(ProcessID pid)
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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{
Kernel: Make sys$disown not require the big lock This syscall had a TOCTOU where it checked the peer's PPID before locking the protected data (where the PPID is stored). After closing the race window, we can mark the syscall as not needing the big lock.
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VERIFY_NO_PROCESS_BIG_LOCK(this);
Kernel: Handle promise violations in the syscall handler Previously we would crash the process immediately when a promise violation was found during a syscall. This is error prone, as we don't unwind the stack. This means that in certain cases we can leak resources, like an OwnPtr / RefPtr tracked on the stack. Or even leak a lock acquired in a ScopeLockLocker. To remedy this situation we move the promise violation handling to the syscall handler, right before we return to user space. This allows the code to follow the normal unwind path, and grantees there is no longer any cleanup that needs to occur. The Process::require_promise() and Process::require_no_promises() functions were modified to return ErrorOr<void> so we enforce that the errors are always propagated by the caller.
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TRY(require_promise(Pledge::proc));
Kernel: Add support for jails Our implementation for Jails resembles much of how FreeBSD jails are working - it's essentially only a matter of using a RefPtr in the Process class to a Jail object. Then, when we iterate over all processes in various cases, we could ensure if either the current process is in jail and therefore should be restricted what is visible in terms of PID isolation, and also to be able to expose metadata about Jails in /sys/kernel/jails node (which does not reveal anything to a process which is in jail). A lifetime model for the Jail object is currently plain simple - there's simpy no way to manually delete a Jail object once it was created. Such feature should be carefully designed to allow safe destruction of a Jail without the possibility of releasing a process which is in Jail from the actual jail. Each process which is attached into a Jail cannot leave it until the end of a Process (i.e. when finalizing a Process). All jails are kept being referenced in the JailManagement. When a last attached process is finalized, the Jail is automatically destroyed.
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auto process = Process::from_pid_in_same_jail(pid);
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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if (!process)
Kernel: Make all syscall functions return KResultOr<T> This makes it a lot easier to return errors since we no longer have to worry about negating EFOO errors and can just return them flat.
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return ESRCH;
Kernel: Make sys$disown not require the big lock This syscall had a TOCTOU where it checked the peer's PPID before locking the protected data (where the PPID is stored). After closing the race window, we can mark the syscall as not needing the big lock.
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TRY(process->with_mutable_protected_data([this](auto& protected_data) -> ErrorOr<void> {
if (protected_data.ppid != this->pid())
return ECHILD;
Kernel: Guard Process "protected data" with a spinlock This ensures that both mutable and immutable access to the protected data of a process is serialized. Note that there may still be multiple TOCTOU issues around this, as we have a bunch of convenience accessors that make it easy to introduce them. We'll need to audit those as well.
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protected_data.ppid = 0;
Kernel: Make sys$disown not require the big lock This syscall had a TOCTOU where it checked the peer's PPID before locking the protected data (where the PPID is stored). After closing the race window, we can mark the syscall as not needing the big lock.
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return {};
}));
Kernel: disown should unblock any potential waiters This is necessary because if a process changes the state to Stopped or resumes from that state, a wait entry is created in the parent process. So, if a child process does this before disown is called, we need to clear those entries to avoid leaking references/zombies that won't be cleaned up until the former parent exits. This also should solve an even more unlikely corner case where another thread is waiting on a pid that is being disowned by another thread.
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process->disowned_by_waiter(*this);
Kernel+LibC: Add sys$disown() for disowning child processes This syscall allows a parent process to disown a child process, setting its parent PID to 0. Unparented processes are automatically reaped by the kernel upon exit, and no sys$waitid() is required. This will make it much nicer to do spawn-and-forget which is common in the GUI environment.
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return 0;
}
}
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