[PATCH 3/9] setpriv: dump user and group info

[Patrick Steinhardt]

setpriv from util-linux has an option to dump the current state
regarding privilege settings via `--dump`. It prints out information on
the real and effective user and group IDs, supplementary groups, the
no-new-privs flag, the capability sets as well as secure bits.

This patch is the start of supporting this mode. To make introduction of
the `--dump` easier to reason about, its introduction has been split
into multiple patches. This particular one introduces the ability to
print out user and group information of the current process.
---
 util-linux/setpriv.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 2 deletions(-)

diff --git a/util-linux/setpriv.c b/util-linux/setpriv.c
index 24e577131..ca31c0a77 100644
--- a/util-linux/setpriv.c
+++ b/util-linux/setpriv.c
@@ -24,6 +24,7 @@
 //usage:	"[OPTIONS] PROG [ARGS]"
 //usage:#define setpriv_full_usage "\n\n"
 //usage:       "Run PROG with different privilege settings\n"
+//usage:     "\n-d,--dump		Show current capabilities"
 //usage:     "\n--nnp,--no-new-privs	Ignore setuid/setgid bits and file capabilities"
 
 //setpriv from util-linux 2.28:
@@ -45,6 +46,7 @@
 // --apparmor-profile <pr>  set AppArmor profile
 
 #include <sys/prctl.h>
+#include <unistd.h>
 #include "libbb.h"
 
 #ifndef PR_SET_NO_NEW_PRIVS
@@ -52,13 +54,56 @@
 #endif
 
 enum {
-	OPT_NNP = (1 << 0),
+	OPT_DUMP = (1 << 0),
+	OPT_NNP  = (1 << 1),
 };
 
+static int dump(void)
+{
+	uid_t ruid, euid, suid;
+	gid_t rgid, egid, sgid;
+	gid_t *gids;
+	int ngids;
+
+	if (getresuid(&ruid, &euid, &suid) < 0)
+		bb_simple_perror_msg_and_die("getresgid");
+
+	if (getresgid(&rgid, &egid, &sgid) < 0)
+		bb_simple_perror_msg_and_die("getresgid");
+
+	if ((ngids = getgroups(0, NULL)) < 0)
+		bb_simple_perror_msg_and_die("getgroups");
+	gids = xmalloc(ngids * sizeof(*gids));
+	if ((ngids = getgroups(ngids, gids)) < 0)
+		bb_simple_perror_msg_and_die("getgroups");
+
+	printf("uid: %d\n", ruid);
+	printf("euid: %d\n", euid);
+	printf("gid: %d\n", rgid);
+	printf("egid: %d\n", egid);
+
+	printf("Supplementary groups: ");
+	if (ngids == 0) {
+		printf("[none]");
+	} else {
+		int i;
+		for (i = 0; i < ngids; i++) {
+			if (i)
+				putchar(',');
+			printf("%d", gids[i]);
+		}
+	}
+	putchar('\n');
+
+	free(gids);
+	return 0;
+}
+
 int setpriv_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int setpriv_main(int argc UNUSED_PARAM, char **argv)
 {
 	static const char setpriv_longopts[] ALIGN1 =
+		"dump\0"         No_argument	"d"
 		"nnp\0"          No_argument	"\xff"
 		"no-new-privs\0" No_argument	"\xff"
 		;
@@ -66,11 +111,18 @@ int setpriv_main(int argc UNUSED_PARAM, char **argv)
 
 	opt_complementary = "";
 	applet_long_options = setpriv_longopts;
-	opts = getopt32(argv, "+");
+	opts = getopt32(argv, "+d");
 
 	argc -= optind;
 	argv += optind;
 
+	if (opts & OPT_DUMP) {
+		if ((opts & ~OPT_DUMP) || argc)
+			bb_error_msg_and_die("setpriv: --dump is incompatible with all other options");
+
+		return dump();
+	}
+
 	if (!argc)
 		bb_error_msg_and_die("no program specified");
 
-- 
2.13.2