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Kernel: Track allocated FileDescriptionAndFlag elements in each Process

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The way the Process::FileDescriptions::allocate() API works today means
that two callers who allocate back to back without associating a
FileDescription with the allocated FD, will receive the same FD and thus
one will stomp over the other.

Naively tracking which FileDescriptions are allocated and moving onto
the next would introduce other bugs however, as now if you "allocate"
a fd and then return early further down the control flow of the syscall
you would leak that fd.

This change modifies this behavior by tracking which descriptions are
allocated and then having an RAII type to "deallocate" the fd if the
association is not setup the end of it's scope.
This commit is contained in:
Brian Gianforcaro 2021-07-27 23:59:24 -07:00 • committed by Andreas Kling
parent ba03b6ad02
commit 4b2651ddab
11 changed files with 104 additions and 45 deletions
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23
Kernel/Process.cpp
View file

@ -169,9 +169,14 @@ RefPtr<Process> Process::create_user_process(RefPtr<Thread>& first_thread, const
}
auto& device_to_use_as_tty = tty ? (CharacterDevice&)*tty : NullDevice::the();
auto description = device_to_use_as_tty.open(O_RDWR).value();
process->m_fds[0].set(*description);
process->m_fds[1].set(*description);
process->m_fds[2].set(*description);
auto setup_description = [&process, &description](int fd) {
process->m_fds.m_fds_metadatas[fd].allocate();
process->m_fds[fd].set(*description);
};
setup_description(0);
setup_description(1);
setup_description(2);
error = process->exec(path, move(arguments), move(environment));
if (error != 0) {
@ -411,11 +416,13 @@ RefPtr<Process> Process::from_pid(ProcessID pid)
const Process::FileDescriptionAndFlags& Process::FileDescriptions::at(size_t i) const
{
ScopedSpinLock lock(m_fds_lock);
VERIFY(m_fds_metadatas[i].is_allocated());
return m_fds_metadatas[i];
}
Process::FileDescriptionAndFlags& Process::FileDescriptions::at(size_t i)
{
ScopedSpinLock lock(m_fds_lock);
VERIFY(m_fds_metadatas[i].is_allocated());
return m_fds_metadatas[i];
}
@ -465,14 +472,16 @@ size_t Process::FileDescriptions::open_count() const
return count;
}
KResultOr<int> Process::FileDescriptions::allocate(int first_candidate_fd)
KResultOr<Process::ScopedDescriptionAllocation> Process::FileDescriptions::allocate(int first_candidate_fd)
{
ScopedSpinLock lock(m_fds_lock);
for (size_t i = first_candidate_fd; i < max_open(); ++i) {
if (!m_fds_metadatas[i])
return i;
if (!m_fds_metadatas[i].is_allocated()) {
m_fds_metadatas[i].allocate();
return Process::ScopedDescriptionAllocation { static_cast<int>(i), &m_fds_metadatas[i] };
}
}
return KResult(EMFILE);
return EMFILE;
}
Time kgettimeofday()