This adds support for MS_RDONLY, a mount flag that tells the kernel to disallow
any attempts to write to the newly mounted filesystem. As this flag is
per-mount, and different mounts of the same filesystems (such as in case of bind
mounts) can have different mutability settings, you have to go though a custody
to find out if the filesystem is mounted read-only, instead of just asking the
filesystem itself whether it's inherently read-only.
This also adds a lot of checks we were previously missing; and moves some of
them to happen after more specific checks (such as regular permission checks).
One outstanding hole in this system is sys$mprotect(PROT_WRITE), as there's no
way we can know if the original file description this region has been mounted
from had been opened through a readonly mount point. Currently, we always allow
such sys$mprotect() calls to succeed, which effectively allows anyone to
circumvent the effect of MS_RDONLY. We should solve this one way or another.
VFS no longer deals with inodes in public API, only with custodies and file
descriptions. Talk directly to the file system if you need to operate on a
inode. In most cases you actually want to go though VFS, to get proper
permission check and other niceties. For this to work, you have to provide a
custody, which describes *how* you have opened the inode, not just what the
inode is.
And move canonicalized_path() to a static method on LexicalPath.
This is to make it clear that FileSystemPath/canonicalized_path() only
perform *lexical* canonicalization.
In contrast to the previous patchset that was reverted, this time we use
a "special" method to access a file with block size of 512 bytes (like
a harddrive essentially).
Also, duplicate data in dbg() and klog() calls were removed.
In addition, leakage of virtual address to kernel log is prevented.
This is done by replacing kprintf() calls to dbg() calls with the
leaked data instead.
Also, other kprintf() calls were replaced with klog().
If we get an -ENOENT when resolving the target because of some part, that is not
the very last part, missing, we should just return the error instead of panicking
later :^)
To test:
$ mkdir /tmp/foo/
$ mv /tmp/foo/ /tmp/bar/
Related to https://github.com/SerenityOS/serenity/issues/1253
This is apparently a special case unlike any other, so let's handle it
directly in VFS::mkdir() instead of adding an alternative code path into
VFS::resolve_path().
Fixes https://github.com/SerenityOS/serenity/issues/1253
Previously this API would return an InodeIdentifier, which meant that
there was a race in path resolution where an inode could be unlinked
in between finding the InodeIdentifier for a path component, and
actually resolving that to an Inode object.
Attaching a test that would quickly trip an assertion before.
Test: Kernel/path-resolution-race.cpp
When using dbg() in the kernel, the output is automatically prefixed
with [Process(PID:TID)]. This makes it a lot easier to understand which
thread is generating the output.
This patch also cleans up some common logging messages and removes the
now-unnecessary "dbg() << *current << ..." pattern.
Sergey suggested that having a non-zero O_RDONLY would make some things
less confusing, and it seems like he's right about that.
We can now easily check read/write permissions separately instead of
dancing around with the bits.
This patch also fixes unveil() validation for O_RDWR which previously
forgot to check for "r" permission.
This syscall is a complement to pledge() and adds the same sort of
incremental relinquishing of capabilities for filesystem access.
The first call to unveil() will "drop a veil" on the process, and from
now on, only unveiled parts of the filesystem are visible to it.
Each call to unveil() specifies a path to either a directory or a file
along with permissions for that path. The permissions are a combination
of the following:
- r: Read access (like the "rpath" promise)
- w: Write access (like the "wpath" promise)
- x: Execute access
- c: Create/remove access (like the "cpath" promise)
Attempts to open a path that has not been unveiled with fail with
ENOENT. If the unveiled path lacks sufficient permissions, it will fail
with EACCES.
Like pledge(), subsequent calls to unveil() with the same path can only
remove permissions, not add them.
Once you call unveil(nullptr, nullptr), the veil is locked, and it's no
longer possible to unveil any more paths for the process, ever.
This concept comes from OpenBSD, and their implementation does various
things differently, I'm sure. This is just a first implementation for
SerenityOS, and we'll keep improving on it as we go. :^)
Previously, VFS::open() would only use the passed flags for permission checking
purposes, and Process::sys$open() would set them on the created FileDescription
explicitly. Now, they should be set by VFS::open() on any files being opened,
including files that the kernel opens internally.
This also lets us get rid of the explicit check for whether or not the returned
FileDescription was a preopen fd, and in fact, fixes a bug where a read-only
preopen fd without any other flags would be considered freshly opened (due to
O_RDONLY being indistinguishable from 0) and granted a new set of flags.
As suggested by Joshua, this commit adds the 2-clause BSD license as a
comment block to the top of every source file.
For the first pass, I've just added myself for simplicity. I encourage
everyone to add themselves as copyright holders of any file they've
added or modified in some significant way. If I've added myself in
error somewhere, feel free to replace it with the appropriate copyright
holder instead.
Going forward, all new source files should include a license header.
Symlink resolution is now a virtual method on an inode,
Inode::resolve_as_symlink(). The default implementation just reads the stored
inode contents, treats them as a path and calls through to VFS::resolve_path().
This will let us support other, magical files that appear to be plain old
symlinks but resolve to something else. This is particularly useful for ProcFS.
It turns out we don't even need to store the whole custody chain, as we only
ever access its last element. So we can just store one custody. This also fixes
a performance FIXME :^)
Also, rename parent_custody to out_parent.
This makes the implementation easier to follow, but also fixes multiple issues
with the old implementation. In particular, it now deals properly with . and ..
in paths, including around mount points.
Hopefully there aren't many new bugs this introduces :^)
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.
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.
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.
