[PATCH v1 3/3] policycoreutils/setfiles: honor RESTORECON_THREADS

From: Johnny Boero <[email protected]>

Relabeling is invoked from places that cannot reasonably be given a -T
option.  On a Fedora 44 system, 10 installed packages run restorecon
from their scriptlets -- filesystem, kernel-core, container-selinux and
selinux-policy-targeted among them -- and not one of them passes -T:

  restorecon -R /usr/bin /usr/sbin
  restorecon -e /run/media -R /root /var/log /var/run /etc/passwd* ...
  restorecon -R /var/lib/containers

Influencing those means patching every spec file in the distribution,
one merge request at a time, and only covers the packages one happens to
have installed.  The environment is the only knob that reaches them all
at once.

Add RESTORECON_THREADS, with the same meaning as -T, which takes
precedence when both are given:

  RESTORECON_THREADS=1 dnf update  # keep relabeling on a single core
  RESTORECON_THREADS=8 dnf update  # cap parallelism during application load

An invalid value is reported and ignored rather than being fatal, since
the variable is inherited by every child process and should not be able
to break an unrelated caller.

This patch stands on its own: it is the brake for the new default in the
preceding patch, and equally the accelerator if the default is left at a
single thread.

Link: https://github.com/SELinuxProject/selinux/issues/489
Signed-off-by: Johnny Boero <[email protected]>
---
 policycoreutils/setfiles/restorecon.8 | 17 ++++++++++++++++-
 policycoreutils/setfiles/setfiles.8   | 18 +++++++++++++++++-
 policycoreutils/setfiles/setfiles.c   | 19 +++++++++++++++++--
 3 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/policycoreutils/setfiles/restorecon.8 b/policycoreutils/setfiles/restorecon.8
index 8d7b46f0..001039b7 100644
--- a/policycoreutils/setfiles/restorecon.8
+++ b/policycoreutils/setfiles/restorecon.8
@@ -187,8 +187,23 @@ use up to
 .I nthreads
 threads.  Specify 0 to create as many threads as there are available
 CPU cores (default); 1 to use only a single thread; or any positive
-number to use the given number of threads (if possible).
+number to use the given number of threads (if possible).  This option
+overrides the
+.B RESTORECON_THREADS
+environment variable.
+.SH "ENVIRONMENT"
 .TP
+.B RESTORECON_THREADS
+Sets the default number of threads to use, with the same meaning as the
+.B \-T
+option.  This allows the amount of parallelism to be controlled for
+callers that do not pass
+.B \-T
+themselves, such as package installation scripts.  Setting it to 1
+restores the historic single threaded behaviour.  An invalid value is
+ignored with a warning.  The
+.B \-T
+option takes precedence.
 .SH "ARGUMENTS"
 .IR pathname \ ...
 The pathname for the file(s) to be relabeled.
diff --git a/policycoreutils/setfiles/setfiles.8 b/policycoreutils/setfiles/setfiles.8
index 53cb97cc..101556a9 100644
--- a/policycoreutils/setfiles/setfiles.8
+++ b/policycoreutils/setfiles/setfiles.8
@@ -192,12 +192,28 @@ use up to
 .I nthreads
 threads.  Specify 0 to create as many threads as there are available
 CPU cores (default); 1 to use only a single thread; or any positive
-number to use the given number of threads (if possible).
+number to use the given number of threads (if possible).  This option
+overrides the
+.B RESTORECON_THREADS
+environment variable.
 .TP
 .B \-A
 do not track inodes with multiple hard links or bind mounts that would
 match different contexts (saves memory)
 
+.SH "ENVIRONMENT"
+.TP
+.B RESTORECON_THREADS
+Sets the default number of threads to use, with the same meaning as the
+.B \-T
+option.  This allows the amount of parallelism to be controlled for
+callers that do not pass
+.B \-T
+themselves, such as package installation scripts.  Setting it to 1
+restores the historic single threaded behaviour.  An invalid value is
+ignored with a warning.  The
+.B \-T
+option takes precedence.
 .SH "ARGUMENTS"
 .TP
 .I spec_file
diff --git a/policycoreutils/setfiles/setfiles.c b/policycoreutils/setfiles/setfiles.c
index 4c860755..ee0930b7 100644
--- a/policycoreutils/setfiles/setfiles.c
+++ b/policycoreutils/setfiles/setfiles.c
@@ -65,8 +65,8 @@ static void set_rootpath(const char *arg)
 }
 
 /*
- * Parse a thread count, as given by the -T option.  Returns -1 on invalid
- * input.
+ * Parse a thread count, as given by the -T option or the
+ * RESTORECON_THREADS environment variable.  Returns -1 on invalid input.
  */
 static int parse_nthreads(const char *str, size_t *nthreads)
 {
@@ -166,6 +166,7 @@ int main(int argc, char **argv)
 	struct stat sb;
 	int opt, i = 0;
 	const char *input_filename = NULL;
+	const char *env_nthreads;
 	int use_input_file = 0;
 	char *buf = NULL;
 	size_t buf_len = 0, nthreads = 0;
@@ -246,6 +247,20 @@ int main(int argc, char **argv)
 			exit(0);
 	}
 
+	/*
+	 * An explicit -T option takes precedence over the environment.  An
+	 * invalid value is not fatal, so that a bogus setting inherited by
+	 * every child process does not break unrelated callers.
+	 */
+	env_nthreads = getenv("RESTORECON_THREADS");
+	if (env_nthreads && env_nthreads[0] != '\0' &&
+	    parse_nthreads(env_nthreads, &nthreads) < 0) {
+		fprintf(stderr,
+			"%s:  invalid RESTORECON_THREADS value \"%s\", ignoring\n",
+			r_opts.progname, env_nthreads);
+		nthreads = 0;
+	}
+
 	/* Process any options. */
 	while ((opt = getopt(argc, argv, opts)) > 0) {
 		switch (opt) {
-- 
2.55.0