We have a problem with the original utimensat syscall because when we
do call LibC futimens function, internally we provide an empty path,
and the Kernel get_syscall_path_argument method will detect this as an
invalid path.
This happens to spit an error for example in the touch utility, so if a
user is running "touch non_existing_file", it will create that file, but
the user will still see an error coming from LibC futimens function.
This new syscall gets an open file description and it provides the same
functionality as utimensat, on the specified open file description.
The new syscall will be used later by LibC to properly implement LibC
futimens function so the situation described with relation to the
"touch" utility could be fixed.
We were detaching from the jail process list too early. To ensure we
detach properly, leverage the remove_from_secondary_lists method
so the possibly jailed parent process can still see the dying process
and therefore clean it properly.
Instead of setting up the new address space on it's own, and only swap
to the new address space at the end, we now immediately swap to the new
address space (while still keeping the old one alive) and only revert
back to the old one if we fail at any point.
This is done to ensure that the process' active address space (aka the
contents of m_space) always matches actual address space in use by it.
That should allow us to eventually make the page fault handler process-
aware, which will let us properly lock the process address space lock.
The SID was duplicated between the process credentials and protected
data. And to make matters worse, the credentials SID was not updated in
sys$setsid.
This patch fixes this by removing the SID from protected data and
updating the credentials SID everywhere.
Now that it's no longer using LockRefPtr, we can actually move it into
protected data. (LockRefPtr couldn't be stored there because protected
data is immutable at times, and LockRefPtr uses some of its own bits
for locking.)
...and also make the Process tick counters clock_t instead of u32.
It seems harmless to get interrupted in the middle of reading these
counters and reporting slightly fewer ticks in some category.
These were stored in a bunch of places. The main one that's a bit iffy
is the Mutex::m_holder one, which I'm going to simplify in a subsequent
commit.
In Plan9FS and WorkQueue, we can't make the NNRPs const due to
initialization order problems. That's probably doable with further
cleanup, but left as an exercise for our future selves.
Before starting this, I expected the thread blockers to be a problem,
but as it turns out they were super straightforward (for once!) as they
don't mutate the thread after initiating a block, so they can just use
simple const-ified NNRPs.
- Instead of taking the first new thread as an out-parameter, we now
bundle the process and its first thread in a struct and use that
as the return value.
- Make all Process factory functions return ErrorOr. Use this to convert
some places to more TRY().
- Drop the "try_" prefix on Process factory functions.
The only persistent one of these was Thread::m_process and that never
changes after initialization. Make it const to enforce this and switch
everything over to RefPtr & NonnullRefPtr.
It makes much more sense to have these actions being performed via the
prctl syscall, as they both require 2 plain arguments to be passed to
the syscall layer, and in contrast to most syscalls, we don't get in
these removed syscalls an automatic representation of Userspace<T>, but
two FlatPtr(s) to perform casting on them in the prctl syscall which is
suited to what has been done in the removed syscalls.
Also, it makes sense to have these actions in the prctl syscall, because
they are strongly related to the process control concept of the prctl
syscall.
This is done with 2 major steps:
1. Remove JailManagement singleton and use a structure that resembles
what we have with the Process object. This is required later for the
second step in this commit, but on its own, is a major change that
removes this clunky singleton that had no real usage by itself.
2. Use IntrusiveLists to keep references to Process objects in the same
Jail so it will be much more straightforward to iterate on this kind
of objects when needed. Previously we locked the entire Process list
and we did a simple pointer comparison to check if the checked
Process we iterate on is in the same Jail or not, which required
taking multiple Spinlocks in a very clumsy and heavyweight way.
This patch switches away from {Nonnull,}LockRefPtr to the non-locking
smart pointers throughout the kernel.
I've looked at the handful of places where these were being persisted
and I don't see any race situations.
Note that the process file descriptor table (Process::m_fds) was already
guarded via MutexProtected.
Since the ProcFS doesn't hold many global objects within it, the need
for a fully-structured design of backing components and a registry like
with the SysFS is no longer true.
To acommodate this, let's remove all backing store and components of the
ProcFS, so now it resembles what we had in the early days of ProcFS in
the project - a mostly-static filesystem, with very small amount of
kmalloc allocations needed.
We still use the inode index mechanism to understand the role of each
inode, but this is done in a much "static"ier way than before.
This is done by merging all scattered pieces of derived classes from the
ProcFSInode class into that one class, so we don't use inheritance but
rather simplistic checks to determine the proper code for each ProcFS
inode with its specific characteristics.
Before this patch, Core::SessionManagement::parse_path_with_sid() would
figure out the root session ID by sifting through /sys/kernel/processes.
That file can take quite a while to generate (sometimes up to 40ms on my
machine, which is a problem on its own!) and with no caching, many of
our programs were effectively doing this multiple times on startup when
unveiling something in /tmp/session/%sid/
While we should find ways to make generating /sys/kernel/processes fast
again, this patch addresses the specific problem by introducing a new
syscall: sys$get_root_session_id(). This extracts the root session ID
by looking directly at the process table and takes <1ms instead of 40ms.
This cuts WebContent process startup time by ~100ms on my machine. :^)
We really don't want callers of this function to accidentally change
the jail, or even worse - remove the Process from an attached jail.
To ensure this never happens, we can just declare this method as const
so nobody can mutate it this way.
Use this helper function in various places to replace the old code of
acquiring the SpinlockProtected<RefPtr<Jail>> of a Process to do that
validation.
`inline` already assigns vague linkage, so there's no need to
also assign per-TU linkage. Allows the linker to dedup these
functions across TUs (and is almost always just the Right Thing
to do in C++ -- this ain't C).
This step would ideally not have been necessary (increases amount of
refactoring and templates necessary, which in turn increases build
times), but it gives us a couple of nice properties:
- SpinlockProtected inside Singleton (a very common combination) can now
obtain any lock rank just via the template parameter. It was not
previously possible to do this with SingletonInstanceCreator magic.
- SpinlockProtected's lock rank is now mandatory; this is the majority
of cases and allows us to see where we're still missing proper ranks.
- The type already informs us what lock rank a lock has, which aids code
readability and (possibly, if gdb cooperates) lock mismatch debugging.
- The rank of a lock can no longer be dynamic, which is not something we
wanted in the first place (or made use of). Locks randomly changing
their rank sounds like a disaster waiting to happen.
- In some places, we might be able to statically check that locks are
taken in the right order (with the right lock rank checking
implementation) as rank information is fully statically known.
This refactoring even more exposes the fact that Mutex has no lock rank
capabilites, which is not fixed here.
Check if the process we are currently running is in a jail, and if that
is the case, fail early with the EPERM error code.
Also, as Brian noted, we should also disallow attaching to a jail in
case of already running within a setid executable, as this leaves the
user with false thinking of being secure (because you can't exec new
setid binaries), but the current program is still marked setid, which
means that at the very least we gained permissions while we didn't
expect it, so let's block it.
This syscall will be used later on to ensure we can declare virtual
memory mappings as immutable (which means that the underlying Region is
basically immutable for both future annotations or changing the
protection bits of it).
This patch validates that the size of the auxiliary vector does not
exceed `Process::max_auxiliary_size`. The auxiliary vector is a range
of memory in userspace stack where the kernel can pass information to
the process that will be created via `Process:do_exec`.
The reason the kernel needs to validate its size is that the about to
be created process needs to have remaining space on the stack.
Previously only `argv` and `envp` were taken into account for the
size validation, with this patch, the size of `auxv` is also
checked. All three elements contain values that a user (or an
attacker) can specify.
This patch adds the constant `Process::max_auxiliary_size` which is
defined to be one eight of the user-space stack size. This is the
approach taken by `Process:max_arguments_size` and
`Process::max_environment_size` which are used to check the sizes
of `argv` and `envp`.
To accomplish this, we add another VeilState which is called
LockedInherited. The idea is to apply exec unveil data, similar to
execpromises of the pledge syscall, on the current exec'ed program
during the execve sequence. When applying the forced unveil data, the
veil state is set to be locked but the special state of LockedInherited
ensures that if the new program tries to unveil paths, the request will
silently be ignored, so the program will continue running without
receiving an error, but is still can only use the paths that were
unveiled before the exec syscall. This in turn, allows us to use the
unveil syscall with a special utility to sandbox other userland programs
in terms of what is visible to them on the filesystem, and is usable on
both programs that use or don't use the unveil syscall in their code.
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.
The syscalls are renamed as they no longer reflect the exact POSIX
functionality. They can now handle setting/getting scheduler parameters
for both threads and processes.
This is a left-over from back when we didn't have any locking on the
global Process list, nor did we have SMP support, so this acted as some
kind of locking mechanism. We now have proper locks around the Process
list, so this is no longer relevant.
This allows sys$mprotect() to honor the original readable & writable
flags of the open file description as they were at the point we did the
original sys$mmap().
IIUC, this is what Dr. POSIX wants us to do:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/mprotect.html
Also, remove the bogus and racy "W^X" checking we did against mappings
based on their current inode metadata. If we want to do this, we can do
it properly. For now, it was not only racy, but also did blocking I/O
while holding a spinlock.
