This avoids having to do the symlink chasing in GetEmulatedFDPath, since
the kernel does it for us. On top of that, with a merged RootFS
setup, this will correctly handle symlinks from user directories into
the RootFS, fixing wine on Fedora.
With a merged RootFS, all binaries are executed through the RootFS. When
executing a binary that is actually a native binary, we want to do so
outside the RootFS. Handle this by stripping the RootFS prefix in that
case.
If a RootFS symlink links to an absolute path within the RootFS, we need
to strip the RootFS prefix. This would not normally happen with a plain
RootFS, but it can happen if /proc is mounted within the RootFS.
If there's a symlink to / within the RootFS, don't attempt to follow it,
since that will end up trying to look up the empty string within the
RootFS (which is not legal). Just return the symlink.
To locate whether a path is in the emulated list, EmulatedFDManager::OpenAt()
attemps to resolve the path. realpath() ends up calling readlinkat() on
every path component, which is a lot of syscalls for every open()
variant syscall. It also makes interaction with the rootfs complex and
error-prone.
There's a much easier way to do this: We just open the file without
emulation and check its real path via get_fdpath(). This is just one
readlink() syscall per open, instead of one per path component. If the
file turns out to be emulated (uncommon case), we swap out the fds.
This also decouples EmulatedFDManager from guest path resolution
entirely, so it will never fall out of sync with the RootFS logic.
Apparently Chromium/CEF can chroot or otherwise sandbox the filesystem
away before forking and checking for directory FDs, making /proc
inaccessible, which means we can't stat it for our inode check, breaking
the hiding.
So, double down on things and do what Chromium does: open an fd to /proc
ahead of time, so that continues to work. Then we use it to update the
inode of our RootFS fd instead, and finally, also do the /proc fd itself
to hide that one too.
We also don't need to check the st_dev of /proc more than once, since
that's not expected to change anyway.
Fixes cefsimple.
Chromium/CEF has code that iterates through all open FDs and bails if
any are directories (apparently a sandboxing sanity check). To avoid
this check, we need to hide the RootFS FD. This requires hooking all the
getdents variants to skip that entry.
To keep the runtime cost low, we keep track of the inode of
/proc/self/fd/<rootfs fd> (note: not the RootFS inode, the inode of the
magic symlink in /proc), and first do a quick check on that. If it
matches, then we stat the dirfd we are reading and check against the
procfs device, to complete the inode equality check.
As an extra benefit, this also fixes code that tries to iterate and
close all/extra FDs and ends up closing the RootFS fd.
Upstream has rejected this flag which would have let FEX close the gap
in functionality between binfmt_misc interpreters and PT_INTERP
interpreters for how `/proc/exe` is handled. Since we are unable to
change their opinions, just remove the code from FEX since it's never
going to happen.
Removes a little bit of confusing behaviour in execveat and
filemanagement handling. Leaving us with only the regular confusing
behaviour of trying to track accesses to `/proc/exe` instead.
Fixes#3691
We weren't checking if the file was empty before using its `at` function
member. This was causing an early crash if the config file existed but
was empty.
Consolidates the three locations that copy and pasted the json allocator
tools and adds an empty check for all of them.
Also adds two missing checks to the ThunksDB handler that could have
resulted in the same crash if ThunksDB was an empty file.
When asked to not follow the symlink, FEX needs to return data about the
symlink itself rather than following to the target executable. In that
case we need to return symlink information otherwise games that sanity
check can break.
This is what happened with Darwinia in #3662.
We return the FEXInterpreter symlink information in this case since it
doesn't return any information that is relevent to leaking emulator
state. Once the application asks to follow through to the symlink target
is when we will replace.
Also adds a unit test to ensure we don't break it.
This environment variable had an incorrect priority on the configuration
system. The expectation was higher priority than most other layers.
Now the only layer that has higher priority is the environment
variables.
I remember seeing some application last year where they closed a FEX
owned FD but now I don't remember what it was. This can really mess us
up so add some debug tracking so we can try and find it again.
Might be something specifically around flatpack, appimage, or chrome's
sandbox. I have some ideas about how to work around these problems if
they crop up but need to find the problem applications again.
Which requires moving LinuxEmulation to its own independent folder as
well. Since both IRLoader and FEXLoader rely on it.
No functional change, just moves the the code around.
Asahi Lina