From 37295f52bda468527f2a7cbc3aa1fafabb5e8068 Mon Sep 17 00:00:00 2001
From: Mattias Andrée <maandree@kth.se>
Date: Thu, 25 Mar 2021 10:06:27 +0100
Subject: Remove video group membership check and use file permissions and
 ownership instead
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Signed-off-by: Mattias Andrée <maandree@kth.se>
---
 Makefile       |  7 +++++--
 adjbacklight.c | 44 --------------------------------------------
 config.mk      |  2 ++
 3 files changed, 7 insertions(+), 46 deletions(-)

diff --git a/Makefile b/Makefile
index f3b9f72..8cbdd23 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,10 @@ install: adjbacklight
 	cp -- adjbacklight "$(DESTDIR)$(PREFIX)/bin"
 	cp -- adjbacklight.1 "$(DESTDIR)$(MANPREFIX)/man1"
 	cp -- LICENSE "$(DESTDIR)$(PREFIX)/share/licenses/adjbacklight"
-	chmod -- 4755 "$(DESTDIR)$(PREFIX)/bin/adjbacklight"
+
+post-install:
+	chown -- '0:$(VIDEO_GROUP)' "$(DESTDIR)$(PREFIX)/bin/adjbacklight"
+	chmod -- 4754 "$(DESTDIR)$(PREFIX)/bin/adjbacklight"
 
 uninstall:
 	-rm -- "$(DESTDIR)$(PREFIX)/bin/adjbacklight"
@@ -38,4 +41,4 @@ uninstall:
 clean:
 	-rm -rf -- adjbacklight test *.o .testdir
 
-.PHONY: all check install uninstall clean
+.PHONY: all check install post-install uninstall clean
diff --git a/adjbacklight.c b/adjbacklight.c
index 6fa0066..80dd4a5 100644
--- a/adjbacklight.c
+++ b/adjbacklight.c
@@ -226,47 +226,6 @@ handle_device(const char *device, int get, int set, double adj, int inc, const c
 }
 
 
-static void
-check_permissions(void)
-{
-	long int ngroups_max;
-	gid_t *groups;
-	int ngroups;
-	struct group *videogrp = getgrnam("video");
-
-	if (!getuid())
-		return;
-
-	if (!videogrp && errno && errno != ENOENT && errno != ESRCH && errno != EPERM) {
-		/* Note, glibc sets errno to EIO if the group does not exist,
-		 * this is the not the specified behavour by either POSIX or
-		 * glibc, and it would be a security issue to treat it as OK.
-		 * Additionally, EBADF is not treated as OK. */
-		fprintf(stderr, "%s: getgrnam video: %s\n", argv0, strerror(errno));
-		exit(1);
-	} else if (videogrp) {
-		ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
-		if (ngroups_max < 0 || ngroups_max > INT_MAX - 1) {
-			fprintf(stderr, "%s: sysconf _SC_NGROUPS_MAX: %s\n", argv0, strerror(errno));
-			exit(1);
-		}
-		groups = alloca((size_t)ngroups_max * sizeof(*groups));
-		ngroups = getgroups((int)ngroups_max, groups);
-		if (ngroups < 0) {
-			fprintf(stderr, "%s: getgroups: %s\n", argv0, strerror(errno));
-			exit(1);
-		}
-		while (ngroups--)
-			if (groups[ngroups] == videogrp->gr_gid)
-				break;
-		if (ngroups < 0) {
-			fprintf(stderr, "%s: only root and members of the group 'video' may run this command\n", argv0);
-			exit(1);
-		}
-	}
-}
-
-
 static int
 parse_set_argument(const char *str, char *set_prefix, double *set_value, const char **set_suffix)
 {
@@ -429,9 +388,6 @@ main(int argc, char *argv[])
 	if (set && parse_set_argument(set, &set_prefix, &set_value, &set_suffix))
 		usage();
 
-	/* Check permissions (important because the program is installed with set-uid) */
-	check_permissions();
-
 	if (!get && !set) {
 		isinteractive = isatty(STDIN_FILENO);
 		if (isinteractive && init_terminal(&pid, &saved_stty))
diff --git a/config.mk b/config.mk
index 6f50bbb..60571ad 100644
--- a/config.mk
+++ b/config.mk
@@ -1,6 +1,8 @@
 PREFIX = /usr/local
 MANPREFIX = $(PREFIX)/share/man
 
+VIDEO_GROUP = video
+
 CCFLAGS  = -std=c99 -Wall -Wextra -O2
 CPPFLAGS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_XOPEN_SOURCE=700
 LDFLAGS  = -s
-- 
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