On Tue, Apr 25, 2023 at 09:43:38AM -0500, Jonathon Jongsma wrote:
On 4/25/23 8:11 AM, Erik Skultety wrote:
On Mon, Apr 24, 2023 at 03:50:48PM -0500, Jonathon Jongsma wrote:
When running libvirt from the build directory with the 'run' script, it will run as unconfined_t. This can result in unexpected behavior when selinux is enforcing due to the fact that the selinux policies are written assuming that libvirt is running with the system_u:system_r:virtd_t context. This patch adds a new --selinux option to the run script. When this option is specified, it will launch the specified binary using the 'runcon' utility to set its selinux context to the one mentioned above. Since this requires root privileges, setting the selinux context is not the default behavior and must be enabled with the command line switch.
A fiddled with writing custom selinux transition rules to achieve the same thing a couple years back, but never finished it. No wonder, this is a much cleaner approach. I will only comment on the Python side of things, leaving the overall approach and idea commenting to someone else.
Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com> --- run.in | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 50 insertions(+), 6 deletions(-)
diff --git a/run.in b/run.in index c6d3411082..4aa458b791 100644 --- a/run.in +++ b/run.in @@ -40,6 +40,7 @@ # # ---------------------------------------------------------------------- +import argparse import os import os.path import random @@ -59,15 +60,20 @@ def prepend(env, varname, extradir): here = "@abs_builddir@" -if len(sys.argv) < 2: - print("syntax: %s BINARY [ARGS...]" % sys.argv[0], file=sys.stderr)
Since you decided to use argparse (yes please), we can drop ^this if we properly set the arguments with argparse, it'll even generate the help for us. This way it looks only like a partial solution. Argparse has great documentation so you can just take one of the examples they list.
Yeah, I probably should have commented on why I used this 'partial' approach. I tried a few different ways, including adding a positional argument to argparse that would capture the target executable and its arguments like so:
argsparse.add_argument("args", nargs="+")
and then parsing with parser.parse_args() rather than parse_known_args(). But that prevented me from passing arguments to the target binary without inserting a '--' in to indicate that the run script should stop parsing:
Fails: # ./_build/run --selinux ./_build/src/libvirtd --verbose usage: run [--selinux] args [args ...] run: error: unrecognized arguments: --verbose
Works: # ./_build/run --selinux -- ./_build/src/libvirtd --verbose 2023-04-25 14:26:32.175+0000: 1530463: info : libvirt version: 9.3.0 ...
That seemed annoying to me.
Maybe we could keep using parse_known_args() with the 'args' argument defined above, but I have a vague recollection that this caused some other undesirable behavior so I switched back to the version I submitted. I'll try to refresh my memory.
+parser = argparse.ArgumentParser(add_help=False)
Why don't we want the automatic help?
Because then the run script would intercept the --help option and prevent us from passing it to e.g. libvirt or virsh. Maybe that's not something that we really care about, but I made the choice to pass as much through to the executable as possible.
Right, good point. Without trying it myself, could we utilize subparsers for this? IOW, have: ./run binary <binary> <args> where 'binary' is a keyword arg for the run script. Since --help is positional in argparse when you use subparsers, we could have the main parser with help, but the 'binary' subparser without it - that way we could theoretically pass --help to whatever binary we actually want the run script to wrap. Like I said though, I haven't tried ^this so I'm just tossing in whatever I just made up in my head.
+parser.add_argument('--selinux', + action='store_true', + help='Run in the appropriate selinux context') + +opts, args = parser.parse_known_args()
If you want to use ^this, then you need to be aware of prefix matching on the options recognized by Argparse. IOW if one is to pass <args> to the <binary> then none of the <args> can be a prefix of any of the long options argeparse knows about (in this case --selinux), otherwise it'll consume it. Altough unlikely, we should stay on the safe side and use: argparse.ArgumentParser(..., allow_abbrev=False) [1]
[2] https://docs.python.org/3.11/library/argparse.html?highlight=argparse#allow-...
ok, I wasn't aware of that option.
+ +if len(args) < 1: + print("syntax: %s [--selinux] BINARY [ARGS...]" % sys.argv[0], file=sys.stderr) sys.exit(1)
Same here, with argparse ^this is not needed if the args/options are defined correctly.
-prog = sys.argv[1] -args = sys.argv[1:] +prog = args[0]
argparse's parser obj has a 'prog' attribute [2].
I think that's the wrong 'prog' though. That would give me the './run' script, whereas I want the 'libvirtd' program (or whatever) that the user wants to execute.
Sorry, I completely overlooked the lack of 'sys.' in there, you're absolutely right. Erik