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Kernel: Inherit shared buffers when forking

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We need to create a reference for the new PID for each shared buffer
that the process had a reference to. If the process subsequently
get replaced through exec, those references will be dropped again.
But if exec for some reason fails then other code, such as global
destructors could still expect having access to them.

Fixes #4076
This commit is contained in:
Tom 2020-11-22 15:25:48 -07:00 committed by Andreas Kling
parent 48369194d2
commit a89648e159
Notes: sideshowbarker 2024-07-19 01:18:19 +09:00 
Author: https://github.com/tomuta
Commit: https://github.com/SerenityOS/serenity/commit/a89648e1598
Pull-request: https://github.com/SerenityOS/serenity/pull/4144
Issue: https://github.com/SerenityOS/serenity/issues/4076
3 changed files with 20 additions and 0 deletions
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16
Kernel/SharedBuffer.cpp
View file

@ -121,6 +121,22 @@ void SharedBuffer::share_with(ProcessID peer_pid)
sanity_check("share_with (new ref)");
}
void SharedBuffer::share_all_shared_buffers(Process& from_process, Process& with_process)
{
LOCKER(shared_buffers().lock());
for (auto& shbuf : shared_buffers().resource()) {
auto& shared_buffer = *shbuf.value;
if (shared_buffer.m_global)
continue;
for (auto& ref : shared_buffer.m_refs) {
if (ref.pid == from_process.pid()) {
shared_buffer.share_with(with_process.pid());
break;
}
}
}
}
void SharedBuffer::deref_for_process(Process& process)
{
LOCKER(shared_buffers().lock());

1
Kernel/SharedBuffer.h
View file

@ -70,6 +70,7 @@ public:
void share_globally() { m_global = true; }
void deref_for_process(Process& process);
void disown(ProcessID pid);
static void share_all_shared_buffers(Process& from_process, Process& with_process);
size_t size() const { return m_vmobject->size(); }
void destroy_if_unused();
void seal();

3
Kernel/Syscalls/fork.cpp
View file

@ -27,6 +27,7 @@
#include <Kernel/FileSystem/Custody.h>
#include <Kernel/FileSystem/FileDescription.h>
#include <Kernel/Process.h>
#include <Kernel/SharedBuffer.h>
#include <Kernel/VM/Region.h>
//#define FORK_DEBUG
@ -79,6 +80,8 @@ pid_t Process::sys$fork(RegisterState& regs)
dbg() << "fork: child will begin executing at " << String::format("%w", child_tss.cs) << ":" << String::format("%x", child_tss.eip) << " with stack " << String::format("%w", child_tss.ss) << ":" << String::format("%x", child_tss.esp) << ", kstack " << String::format("%w", child_tss.ss0) << ":" << String::format("%x", child_tss.esp0);
#endif
SharedBuffer::share_all_shared_buffers(*this, *child);
{
ScopedSpinLock lock(m_lock);
for (auto& region : m_regions) {