1 files changed, 241 insertions, 0 deletions
diff --git a/backend/session/direct-ipc.c b/backend/session/direct-ipc.c
new file mode 100644
index 00000000..885662e0
--- /dev/null
+++ b/backend/session/direct-ipc.c
@@ -0,0 +1,241 @@
+#define _POSIX_C_SOURCE 200809L
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/sysmacros.h>
+#include <sys/wait.h>
+#include <xf86drm.h>
+#include <linux/major.h>
+#include <wlr/util/log.h>
+#include "session/direct-ipc.h"
+
+enum { DRM_MAJOR = 226 };
+
+#ifdef HAS_LIBCAP
+#include <sys/capability.h>
+
+static bool have_permissions(void) {
+	cap_t cap = cap_get_proc();
+	cap_flag_value_t val;
+
+	if (!cap || cap_get_flag(cap, CAP_SYS_ADMIN, CAP_PERMITTED, &val) || val != CAP_SET) {
+		wlr_log(L_ERROR, "Do not have CAP_SYS_ADMIN; cannot become DRM master");
+		cap_free(cap);
+		return false;
+	}
+
+	cap_free(cap);
+	return true;
+}
+#else
+static bool have_permissions(void) {
+	if (geteuid() != 0) {
+		wlr_log(L_ERROR, "Do not have root privileges; cannot become DRM master");
+		return false;
+	}
+
+	return true;
+}
+#endif
+
+static void send_msg(int sock, int fd, void *buf, size_t buf_len) {
+	char control[CMSG_SPACE(sizeof(fd))] = {0};
+	struct iovec iovec = { .iov_base = buf, .iov_len = buf_len };
+	struct msghdr msghdr = {0};
+
+	if (buf) {
+		msghdr.msg_iov = &iovec;
+		msghdr.msg_iovlen = 1;
+	}
+
+	if (fd >= 0) {
+		msghdr.msg_control = &control;
+		msghdr.msg_controllen = sizeof(control);
+
+		struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msghdr);
+		*cmsg = (struct cmsghdr) {
+			.cmsg_level = SOL_SOCKET,
+			.cmsg_type = SCM_RIGHTS,
+			.cmsg_len = CMSG_LEN(sizeof(fd)),
+		};
+		memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
+	}
+
+	ssize_t ret;
+	do {
+		ret = sendmsg(sock, &msghdr, 0);
+	} while (ret < 0 && errno == EINTR);
+}
+
+static ssize_t recv_msg(int sock, int *fd_out, void *buf, size_t buf_len) {
+	char control[CMSG_SPACE(sizeof(*fd_out))] = {0};
+	struct iovec iovec = { .iov_base = buf, .iov_len = buf_len };
+	struct msghdr msghdr = {0};
+
+	if (buf) {
+		msghdr.msg_iov = &iovec;
+		msghdr.msg_iovlen = 1;
+	}
+
+	if (fd_out) {
+		msghdr.msg_control = &control;
+		msghdr.msg_controllen = sizeof(control);
+	}
+
+	ssize_t ret;
+	do {
+		ret = recvmsg(sock, &msghdr, MSG_CMSG_CLOEXEC);
+	} while (ret < 0 && errno == EINTR);
+
+	if (fd_out) {
+		struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msghdr);
+		if (cmsg) {
+			memcpy(fd_out, CMSG_DATA(cmsg), sizeof(*fd_out));
+		} else {
+			*fd_out = -1;
+		}
+	}
+
+	return ret;
+}
+
+enum msg_type {
+	MSG_OPEN,
+	MSG_SETMASTER,
+	MSG_DROPMASTER,
+	MSG_END,
+};
+
+struct msg {
+	enum msg_type type;
+	char path[256];
+};
+
+static void communicate(int sock) {
+	struct msg msg;
+	int drm_fd = -1;
+	bool running = true;
+
+	while (running && recv_msg(sock, &drm_fd, &msg, sizeof(msg)) >= 0) {
+		switch (msg.type) {
+		case MSG_OPEN:
+			errno = 0;
+
+			// These are the same flags that logind opens files with
+			int fd = open(msg.path, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
+			int ret = errno;
+			if (fd == -1) {
+				goto error;
+			}
+
+			struct stat st;
+			if (fstat(fd, &st) < 0) {
+				ret = errno;
+				goto error;
+			}
+
+			uint32_t maj = major(st.st_rdev);
+			if (maj != INPUT_MAJOR && maj != DRM_MAJOR) {
+				ret = ENOTSUP;
+				goto error;
+			}
+
+			if (maj == DRM_MAJOR && drmSetMaster(fd)) {
+				ret = errno;
+			}
+error:
+			send_msg(sock, ret ? -1 : fd, &ret, sizeof(ret));
+			close(fd);
+
+			break;
+
+		case MSG_SETMASTER:
+			drmSetMaster(drm_fd);
+			close(drm_fd);
+			send_msg(sock, -1, NULL, 0);
+			break;
+
+		case MSG_DROPMASTER:
+			drmDropMaster(drm_fd);
+			close(drm_fd);
+			send_msg(sock, -1, NULL, 0);
+			break;
+
+		case MSG_END:
+			running = false;
+			send_msg(sock, -1, NULL, 0);
+			break;
+		}
+	}
+
+	close(sock);
+}
+
+int direct_ipc_open(int sock, const char *path) {
+	struct msg msg = { .type = MSG_OPEN };
+	snprintf(msg.path, sizeof(msg.path), "%s", path);
+
+	send_msg(sock, -1, &msg, sizeof(msg));
+
+	int fd, err;
+	recv_msg(sock, &fd, &err, sizeof(err));
+
+	return err ? -err : fd;
+}
+
+void direct_ipc_setmaster(int sock, int fd) {
+	struct msg msg = { .type = MSG_SETMASTER };
+
+	send_msg(sock, fd, &msg, sizeof(msg));
+	recv_msg(sock, NULL, NULL, 0);
+}
+
+void direct_ipc_dropmaster(int sock, int fd) {
+	struct msg msg = { .type = MSG_DROPMASTER };
+
+	send_msg(sock, fd, &msg, sizeof(msg));
+	recv_msg(sock, NULL, NULL, 0);
+}
+
+void direct_ipc_finish(int sock, pid_t pid) {
+	struct msg msg = { .type = MSG_END };
+
+	send_msg(sock, -1, &msg, sizeof(msg));
+	recv_msg(sock, NULL, NULL, 0);
+
+	waitpid(pid, NULL, 0);
+}
+
+int direct_ipc_start(pid_t *pid_out) {
+	if (!have_permissions()) {
+		return -1;
+	}
+
+	int sock[2];
+	if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sock) < 0) {
+		wlr_log_errno(L_ERROR, "Failed to create socket pair");
+		return -1;
+	}
+
+	pid_t pid = fork();
+	if (pid < 0) {
+		wlr_log_errno(L_ERROR, "Fork failed");
+		close(sock[0]);
+		close(sock[1]);
+		return -1;
+	} else if (pid == 0) {
+		close(sock[0]);
+		communicate(sock[1]);
+		_Exit(0);
+	}
+
+	close(sock[1]);
+	*pid_out = pid;
+	return sock[0];
+}