Rewrite the backlight script into a setuid C program

4 files changed, 163 insertions, 29 deletions

diff --git a/bin/.gitignore b/bin/.gitignore
index b1a17ba..4711d71 100644
--- a/bin/.gitignore
+++ b/bin/.gitignore
@@ -1 +1,2 @@
 zzz
+backlight
diff --git a/bin/Makefile b/bin/Makefile
index c7e37e6..b0a8dd1 100644
--- a/bin/Makefile
+++ b/bin/Makefile
@@ -5,8 +5,11 @@ install-zzz: zzz
 	install -D -o root -g root -m 755 zzz /sbin/
 	chmod 6755 /sbin/zzz
 
+install-linux: backlight
+	install -D -o root -g root -m 755 backlight /sbin/
+	chmod 6755 /sbin/backlight
+
 linux:
-	install backlight $(HOME)/bin
 	install wpa $(HOME)/bin
 
 install:
diff --git a/bin/backlight b/bin/backlight
deleted file mode 100755
index a0d6176..0000000
--- a/bin/backlight
+++ /dev/null
@@ -1,28 +0,0 @@
-#!/bin/sh
-set -e
-set -x
-# Note the trailing slash
-base="/sys/class/backlight/amdgpu_bl0/"
-# base="/sys/class/backlight/intel_backlight/"
-# pinebook
-# base="/sys/class/backlight/backlight/"
-_backlight="${base}brightness"
-_max="${base}max_brightness"
-_max="$(awk '{print $1/100;}' < "$_max")"
-
-percent="$(echo "$1" | awk '{print int($1*'"$_max"');}')"
-
-if ! [ -w "$_backlight" ] ; then
-	sudo chgrp "$(id -g)" "$_backlight"
-	sudo chmod g+w "$_backlight"
-fi
-
-
-sh -c "echo \"$percent\" > $_backlight"
-
-## If you want to do this withotu a password:
-# %wheel ALL=(ALL) NOPASSWD: /usr/bin/chgrp 1001 /sys/class/backlight/amdgpu_bl0/brightness
-# %wheel ALL=(ALL) NOPASSWD: /usr/bin/chmod g+w /sys/class/backlight/amdgpu_bl0/brightness
-# %wheel ALL=(ALL) NOPASSWD: /usr/bin/chgrp 1001 /sys/class/backlight/intel_backlight/brightness
-# %wheel ALL=(ALL) NOPASSWD: /usr/bin/chmod g+w /sys/class/backlight/intel_backlight/brightness
-
diff --git a/bin/backlight.c b/bin/backlight.c
new file mode 100644
index 0000000..5894cd8
--- /dev/null
+++ b/bin/backlight.c
@@ -0,0 +1,158 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <string.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <errno.h>
+
+const char *backlight_f[] = {
+	"/sys/class/backlight/intel_backlight/",
+	"/sys/class/backlight/amdgpu_bl0/",
+};
+
+void
+die(const char *msg)
+{
+	puts(msg);
+	exit(1);
+}
+
+void
+err(const char *msg)
+{
+	perror(msg);
+	exit(1);
+}
+
+void*
+ecalloc(size_t nmemb, size_t size)
+{
+	void *ret = calloc(nmemb, size);
+	if (!ret)
+		err("ecalloc");
+	return ret;
+}
+
+char*
+appendStr(size_t len, const char *a, const char *b)
+{
+	char *buf = ecalloc(len, sizeof(char));
+	int ret = snprintf(buf, len, "%s%s", a, b);
+	if (ret == -1 || ret > len)
+		err("snprintf");
+	return buf;
+}
+
+/* returns errno */
+int
+maxBrightness(const char *prefix, long *max)
+{
+	int e;
+	char *buf = appendStr(256, prefix, "/max_brightness");
+
+	int fd = open(buf, O_RDONLY);
+	if (fd == -1) {
+		e = errno;
+		free(buf);
+		return e;
+	}
+
+	memset(buf, '\0', 256);
+
+	int b = read(fd, buf, 256);
+	if (b==-1) {
+		e = errno;
+		free(buf);
+		close(fd);
+		return e;
+	}
+
+	for (int i=0; i<256 ; i++) {
+		if (buf[i] == '\n') {
+			buf[i] = '\0';
+			break;
+		}
+	}
+
+	long n = strtol(buf, NULL, 10);
+	if (n == LONG_MIN || n == LONG_MAX || n == 0)
+		err("strtol");
+
+	free(buf);
+	buf = NULL;
+	close(fd);
+	*max = n;
+
+	return 0;
+}
+
+int
+setBacklight(const char *prefix, int percent)
+{
+	char *fn = appendStr(256, prefix, "/brightness");
+
+	int fd = open(fn, O_WRONLY);
+	if (fd == -1) {
+		free(fn);
+		return -1;
+	}
+
+	int n = dprintf(fd, "%d\n", percent);
+	if (n == -1) {
+		close(fd);
+		free(fn);
+		return -1;
+	}
+	
+	close(fd);
+	free(fn);
+	fn = NULL;
+}
+
+int
+main(int argc, char **argv)
+{
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+	uid_t euid = geteuid();
+	char **a = argv+1;
+	pid_t pid;
+	int ret;
+
+	if (euid != 0)
+		die("Program must be run as root/setuid");
+
+	if (!*a)
+		die("Brightness percentage must be supplied");
+
+
+	long percent = strtol(*a, NULL, 10);
+	if (percent <= LONG_MIN || percent >= LONG_MAX)
+		err("invalid percent");
+	if (percent < 0 || percent > 100)
+		die("percent must be between 0 and 100");
+
+	
+	for (int i=0; i < sizeof(backlight_f)/sizeof(backlight_f[0]); i++) {
+		int ret;
+		long max = 0;
+		ret = maxBrightness(backlight_f[i], &max);
+		if (ret != 0) {
+			const char *msg = strerror(ret);
+			continue;
+		}
+
+		float p = (double)max*((double)percent/100.0);
+
+		ret = setBacklight(backlight_f[i], (int)p);
+		if (ret != 0) {
+			perror("setBacklight");
+		}
+	}
+	
+
+
+
+}