Re: git-daemon --inetd

From

Linus Torvalds <torvalds@osdl.org>

Date

Sep 15, 2005, 16:03 UTC

Message-ID

<Pine.LNX.4.58.0509150829090.26803@g5.osdl.org>

In-Reply-To

<43290EFF.3070604@zytor.com>

On Wed, 14 Sep 2005, H. Peter Anvin wrote:

> 
> On that note, though, it would be very nice if there was a way to run 
> git-daemon in a chroot, or otherwise restrict it to a specific 
> subhierarchy of the filesystem.

It compiles. That's just about all I can say about it.

		Linus

---

diff --git a/daemon.c b/daemon.c
--- a/daemon.c
+++ b/daemon.c
@@ -1,11 +1,19 @@
+/* setresuid/setresgid. GNU? Who are you kidding, glibc? */
+#define _GNU_SOURCE
+
 #include "cache.h"
 #include "pkt-line.h"
 #include <signal.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
 #include <sys/time.h>
+#include <sys/types.h>
 #include <netdb.h>
 #include <netinet/in.h>
+#include <unistd.h>
+
+#include <pwd.h>
+#include <grp.h>
 
 static const char daemon_usage[] = "git-daemon [--inetd | --port=n]";
 
@@ -326,10 +334,50 @@ static int serve(int port)
 	}
 }
 
+/*
+ * This will drop our effective uid/gid to the real one,
+ * even if no "--user=" or "--group=" arguments were used.
+ *
+ * So it's not a no-op even without that.
+ */
+static void set_user_group(const char *user, const char *group)
+{
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+	char *end;
+
+	if (user) {
+		struct passwd *pw = getpwnam(user);
+		if (pw) {
+			uid = pw->pw_uid;
+			gid = pw->pw_gid;
+		} else {
+			uid = strtol(user, &end, 10);
+			if (*end || end == user)
+				die("invalid user name '%s'", user);
+		}
+	}
+	if (group) {
+		struct group *grp = getgrnam(group);
+		if (grp) {
+			gid = grp->gr_gid;
+		} else {
+			gid = strtol(group, &end, 10);
+			if (*end || end == group)
+				die("invalid group name '%s'", group);
+		}
+	}
+	if (!uid || !gid)
+		die("I refuse to run as root");
+	if (setresgid(gid, gid, gid) || setresuid(uid, uid, uid))
+		die("I can't run as %d:%d", uid, gid);
+}
+
 int main(int argc, char **argv)
 {
 	int port = DEFAULT_GIT_PORT;
 	int inetd_mode = 0;
+	const char *user = NULL, *group = NULL;
 	int i;
 
 	for (i = 1; i < argc; i++) {
@@ -350,9 +398,32 @@ int main(int argc, char **argv)
 			continue;
 		}
 
+		if (!strncmp(arg, "--chroot=", 9)) {
+			if (chroot(arg+9) < 0)
+				die("unable to chroot to '%s': %s", arg+9, strerror(errno));
+			if (chdir("/") < 0)
+				die("unable to chdir to new root");
+
+			user = user ? user : "nobody";
+			group = group ? group : "nobody";
+			continue;
+		}
+
+		if (!strncmp(arg, "--user=", 7)) {
+			user = arg+7;
+			continue;
+		}
+
+		if (!strncmp(arg, "--group=", 8)) {
+			group = arg + 8;
+			continue;
+		}
+
 		usage(daemon_usage);
 	}
 
+	set_user_group(user, group);
+
 	if (inetd_mode) {
 		fclose(stderr); //FIXME: workaround
 		return execute();