From 2a453f362d34674b2adfc9f29bb781a0ba7a69c2 Mon Sep 17 00:00:00 2001
From: Evgeny Zinoviev <me@ch1p.com>
Date: Sun, 28 Oct 2018 01:00:03 +0300
Subject: initial

---
 Makefile          |  26 ++++++++++
 README.md         |   1 +
 drm_master_util.c | 151 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 178 insertions(+)
 create mode 100644 Makefile
 create mode 100644 README.md
 create mode 100644 drm_master_util.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..f69be8d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,26 @@
+CC = gcc
+CFLAGS = -O2 -Wall -W
+CFLAGS += `pkg-config --cflags libdrm`
+LDFLAGS = `pkg-config --libs libdrm`
+PROGRAM = drm_master_util
+INSTALL = /usr/bin/install
+PREFIX	= /usr
+
+all: $(PROGRAM)
+
+$(PROGRAM): drm_master_util.o
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
+
+install: $(PROGRAM)
+	$(INSTALL) $(PROGRAM) $(PREFIX)/bin
+	chmod u+s $(PREFIX)/bin/${PROGRAM}
+
+clean:
+	rm -f *.o $(PROGRAM)
+
+distclean: clean
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $^ -I. -o $@
+
+.PHONY: all install clean distclean
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..b923e75
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+# drm_master_util
diff --git a/drm_master_util.c b/drm_master_util.c
new file mode 100644
index 0000000..73884af
--- /dev/null
+++ b/drm_master_util.c
@@ -0,0 +1,151 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <getopt.h>
+#include <errno.h>
+#include <xf86drm.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <string.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <stdbool.h>
+
+#define DRM_HACK_SOCKET_NAME "xorg_drm_master_util"
+
+int recv_fd(int sock)
+{
+    // This function does the arcane magic recving
+    // file descriptors over unix domain sockets
+    struct msghdr msg;
+    struct iovec iov[1];
+    struct cmsghdr *cmsg = NULL;
+    char ctrl_buf[CMSG_SPACE(sizeof(int))];
+    char data[1];
+
+    memset(&msg, 0, sizeof(struct msghdr));
+    memset(ctrl_buf, 0, CMSG_SPACE(sizeof(int)));
+
+    iov[0].iov_base = data;
+    iov[0].iov_len = sizeof(data);
+
+    msg.msg_name = NULL;
+    msg.msg_namelen = 0;
+    msg.msg_control = ctrl_buf;
+    msg.msg_controllen = CMSG_SPACE(sizeof(int));
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+
+    recvmsg(sock, &msg, 0);
+
+    cmsg = CMSG_FIRSTHDR(&msg);
+
+    return *((int *) CMSG_DATA(cmsg));
+}
+
+void usage(const char *name)
+{
+    printf("usage: %s\n", name);
+    printf("\n"
+           "-h, --help:     print this help\n"
+           "-s, --set:      drmSetMaster\n"
+           "-d, --drop:     drmDropMaster\n"
+           "-t, --test:     test\n"
+           "-r, --root:     ensure i'm root\n"
+           "\n");
+}
+
+void check_error(char *prog, int err)
+{
+    if (err) {
+        fprintf(stderr, "%s: %s\n", prog, strerror(errno));
+        exit(err);
+    }
+}
+
+enum action {HELP, SET, DROP, TEST};
+
+int main(int argc, char *argv[])
+{
+    enum action act = HELP;
+    int opt, optindex = 0;
+    int ret = 0;
+    bool ensure_root = false;
+    static struct option longopts[] = {
+        {"help",  0, 0, 'h'},
+        {"set",   0, 0, 's'},
+        {"drop",  0, 0, 'd'},
+        {"test",  0, 0, 't'},
+        {"root",  0, 0, 'r'},
+        {0, 0, 0, 0}
+    };
+
+    if (argv[1] == NULL) {
+        usage(argv[0]);
+        exit(0);
+    }
+
+    while ((opt = getopt_long(argc, argv, "hsdtr",
+                  longopts, &optindex)) != EOF) {
+        switch (opt) {
+        case 's': act = SET;  break;
+        case 'd': act = DROP; break;
+        case 't': act = TEST; break;
+        case 'r': ensure_root = true; break;
+        }
+    }
+
+    if (optind < argc) {
+        fprintf(stderr, "Error: extra parameter found.\n");
+        exit(1);
+    }
+
+    if (ensure_root) {
+        uid_t uid = getuid();
+        uid_t euid = geteuid();
+
+        assert(euid == 0);
+
+        ret = setuid(euid);
+        check_error("setuid", ret);
+
+        uid = getuid();
+        euid = getuid();
+
+        assert(uid == 0);
+    }
+
+    if (act == HELP) {
+        usage(argv[0]);
+        exit(0);
+    }
+
+    struct sockaddr_un addr;
+    int sock;
+
+    // Create and connect a unix domain socket
+    sock = socket(AF_UNIX, SOCK_STREAM, 0);
+    memset(&addr, 0, sizeof(addr));
+    addr.sun_family  = AF_UNIX;
+    strcpy(&addr.sun_path[1], DRM_HACK_SOCKET_NAME);
+    connect(sock, (struct sockaddr *)&addr, sizeof(addr));
+
+    int fd = recv_fd(sock);
+    close(sock);
+
+    assert(fd != 0);
+
+    if (act == SET) {
+        ret = drmSetMaster(fd);
+        check_error("drmSetMaster", ret);
+    } else if (act == DROP) {
+        ret = drmDropMaster(fd);
+        check_error("drmDropMaster", ret);
+    } else if (act == TEST) {
+        printf("received fd: %d\n", fd);
+        dprintf(fd, "drm_master_util: writing to received fd ;)\n");
+    }
+
+    return 0;
+}
-- 
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