You can now bind-mount files and directories. This essentially exposes an
existing part of the file system in another place, and can be used as an
alternative to symlinks or hardlinks.
Here's an example of doing this:
# mkdir /tmp/foo
# mount /home/anon/myfile.txt /tmp/foo -o bind
# cat /tmp/foo
This is anon's file.
We now support these mount flags:
* MS_NODEV: disallow opening any devices from this file system
* MS_NOEXEC: disallow executing any executables from this file system
* MS_NOSUID: ignore set-user-id bits on executables from this file system
The fourth flag, MS_BIND, is defined, but currently ignored.
O_EXEC is mentioned by POSIX, so let's have it. Currently, it is only used
inside the kernel to ensure the process has the right permissions when opening
an executable.
At the moment, the actual flags are ignored, but we correctly propagate them all
the way from the original mount() syscall to each custody that resides on the
mounted FS.
No need to pass around RefPtr<>s and NonnullRefPtr<>s and no need to
heap-allocate them.
Also remove VFS::mount(NonnullRefPtr<FS>&&, StringView path) - it has been
unused for a long time.
In order to preserve the absolute path of the process root, we save the
custody used by chroot() before stripping it to become the new "/".
There's probably a better way to do this.
The chroot() syscall now allows the superuser to isolate a process into
a specific subtree of the filesystem. This is not strictly permanent,
as it is also possible for a superuser to break *out* of a chroot, but
it is a useful mechanism for isolating unprivileged processes.
The VFS now uses the current process's root_directory() as the root for
path resolution purposes. The root directory is stored as an uncached
Custody in the Process object.
As Sergey pointed out, it's silly to have proper entries for . and ..
in TmpFS when we can just synthesize them on the fly.
Note that we have to tolerate removal of . and .. via remove_child()
to keep VFS::rmdir() happy.
This encourages callers to strongly reference file descriptions while
working with them.
This fixes a use-after-free issue where one thread would close() an
open fd while another thread was blocked on it becoming readable.
Test: Kernel/uaf-close-while-blocked-in-read.cpp
Instead of using the FIFO's memory address as part of its absolute path
identity, just use an incrementing FIFO index instead.
Note that this is not used for anything other than debugging (it helps
you identify which file descriptors refer to the same FIFO by looking
at /proc/PID/fds
Supervisor Mode Access Prevention (SMAP) is an x86 CPU feature that
prevents the kernel from accessing userspace memory. With SMAP enabled,
trying to read/write a userspace memory address while in the kernel
will now generate a page fault.
Since it's sometimes necessary to read/write userspace memory, there
are two new instructions that quickly switch the protection on/off:
STAC (disables protection) and CLAC (enables protection.)
These are exposed in kernel code via the stac() and clac() helpers.
There's also a SmapDisabler RAII object that can be used to ensure
that you don't forget to re-enable protection before returning to
userspace code.
THis patch also adds copy_to_user(), copy_from_user() and memset_user()
which are the "correct" way of doing things. These functions allow us
to briefly disable protection for a specific purpose, and then turn it
back on immediately after it's done. Going forward all kernel code
should be moved to using these and all uses of SmapDisabler are to be
considered FIXME's.
Note that we're not realizing the full potential of this feature since
I've used SmapDisabler quite liberally in this initial bring-up patch.
This has been a FIXME for a long time. We now apply the provided
read/write permissions to the constructed FileDescription when opening
a File object via File::open().
We were running without the sticky bit and mode 777, which meant that
the /tmp directory was world-writable *without* protection.
With this fixed, it's no longer possible for everyone to steal root's
files in /tmp.
In order to ensure a specific owner and mode when the local socket
filesystem endpoint is instantiated, we need to be able to call
fchmod() and fchown() on a socket fd between socket() and bind().
This is because until we call bind(), there is no filesystem inode
for the socket yet.
If we're creating something that should have a different owner than the
current process's UID/GID, we need to plumb that all the way through
VFS down to the FS functions.
To accomodate file creation, path resolution optionally returns the
last valid parent directory seen while traversing the path.
Clients will then interpret "ENOENT, but I have a parent for you" as
meaning that the file doesn't exist, but its immediate parent directory
does. The client then goes ahead and creates a new file.
In the case of "/foo/bar/baz" where there is no "/foo", it would fail
with ENOENT and "/" as the last seen parent directory, causing e.g the
open() syscall to create "/baz".
Covered by test_io.
It was previously possible to write to read-only file descriptors,
and read from write-only file descriptors.
All FileDescription objects now start out non-readable + non-writable,
and whoever is creating them has to "manually" enable reading/writing
by calling set_readable() and/or set_writable() on them.
This code never worked, as was never used for anything. We can build
a much better SHM implementation on top of TmpFS or similar when we
get to the point when we need one.
The new PCI subsystem is initialized during runtime.
PCI::Initializer is supposed to be called during early boot, to
perform a few tests, and initialize the proper configuration space
access mechanism. Kernel boot parameters can be specified by a user to
determine what tests will occur, to aid debugging on problematic
machines.
After that, PCI::Initializer should be dismissed.
PCI::IOAccess is a class that is derived from PCI::Access
class and implements PCI configuration space access mechanism via x86
IO ports.
PCI::MMIOAccess is a class that is derived from PCI::Access
and implements PCI configurtaion space access mechanism via memory
access.
The new PCI subsystem also supports determination of IO/MMIO space
needed by a device by checking a given BAR.
In addition, Every device or component that use the PCI subsystem has
changed to match the last changes.
This patch hardens /proc a bit by making many things only accessible
to UID 0, and also disallowing access to /proc/PID/ for anyone other
than the UID of that process (and superuser, obviously.)
Threads now have numeric priorities with a base priority in the 1-99
range.
Whenever a runnable thread is *not* scheduled, its effective priority
is incremented by 1. This is tracked in Thread::m_extra_priority.
The effective priority of a thread is m_priority + m_extra_priority.
When a runnable thread *is* scheduled, its m_extra_priority is reset to
zero and the effective priority returns to base.
This means that lower-priority threads will always eventually get
scheduled to run, once its effective priority becomes high enough to
exceed the base priority of threads "above" it.
The previous values for ThreadPriority (Low, Normal and High) are now
replaced as follows:
Low -> 10
Normal -> 30
High -> 50
In other words, it will take 20 ticks for a "Low" priority thread to
get to "Normal" effective priority, and another 20 to reach "High".
This is not perfect, and I've used some quite naive data structures,
but I think the mechanism will allow us to build various new and
interesting optimizations, and we can figure out better data structures
later on. :^)
This is memory that's loaded from an inode (file) but not modified in
memory, so still identical to what's on disk. This kind of memory can
be freed and reloaded transparently from disk if needed.
