This makes these sandboxing methods stricter when no files are
created or deleted. That is, it's a middle ground between the
initial sandbox and the strictest single-file-to-stdout sandbox:
this allows opening files for reading but output has to go to stdout.
Linux 6.7 added support for ABI version 4 which restricts
TCP connections which xz won't need and thus those can be
forbidden now. Since the ABI version is handled at runtime,
supporting version 4 won't cause any compatibility issues.
Note that new enough kernel headers are required to get
version 4 support enabled at build time.
Landlock is now always used just like pledge(2) is: first in more
permissive mode and later (under certain common conditions) in
a strict mode that doesn't allow opening more files.
I put pledge(2) first in sandbox.c because it's the simplest API
to use and still somewhat fine-grained for basic applications.
So it's the simplest thing to understand for anyone reading sandbox.c.
Also explicitly initialize progress_automatic to make it clear
that it can be read before message_init() sets it. Static variable
was initialized to false by default already so this is only for
clarity.
GCC docs promise that it works and a few other compilers do
too. Clang/LLVM is documented source code only but unsurprisingly
it behaves the same as others on x86-64 at least. But the
certainly-portable way is good enough here so use that.
The x32 port has a x86-64 ABI in term of all registers but uses only
32bit pointer like x86-32. The assembly optimisation fails to compile on
x32. Given the state of x32 I suggest to exclude it from the
optimisation rather than trying to fix it.
Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
It's used only for basic bittrees and fixed-size reverse bittree
because those showed a clear benefit on x86-64 with GCC and Clang.
The other methods were more mixed and thus are commented out but
they should be tested on other archs.
