[PATCH v3 08/20] Introduce passt-repair

[Stefano Brivio <sbrivio@redhat.com>]

A privileged helper to set/clear TCP_REPAIR on sockets on behalf of
passt. Not used yet.

From David's patch: add it to .gitignore, like our other executable
targets.

Co-authored-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 .gitignore     |   1 +
 Makefile       |  10 +++--
 passt-repair.c | 117 +++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 125 insertions(+), 3 deletions(-)
 create mode 100644 passt-repair.c

diff --git a/.gitignore b/.gitignore
index d1c8be9..5824a71 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 /passt.avx2
 /pasta
 /pasta.avx2
+/passt-repair
 /qrap
 /pasta.1
 /seccomp.h
diff --git a/Makefile b/Makefile
index 1383875..1b71cb0 100644
--- a/Makefile
+++ b/Makefile
@@ -42,7 +42,8 @@ PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c flow.c fwd.c \
 	tcp.c tcp_buf.c tcp_splice.c tcp_vu.c udp.c udp_flow.c udp_vu.c util.c \
 	vhost_user.c virtio.c vu_common.c
 QRAP_SRCS = qrap.c
-SRCS = $(PASST_SRCS) $(QRAP_SRCS)
+PASST_REPAIR_SRCS = passt-repair.c
+SRCS = $(PASST_SRCS) $(QRAP_SRCS) $(PASST_REPAIR_SRCS)
 
 MANPAGES = passt.1 pasta.1 qrap.1
 
@@ -72,9 +73,9 @@ mandir		?= $(datarootdir)/man
 man1dir		?= $(mandir)/man1
 
 ifeq ($(TARGET_ARCH),x86_64)
-BIN := passt passt.avx2 pasta pasta.avx2 qrap
+BIN := passt passt.avx2 pasta pasta.avx2 qrap passt-repair
 else
-BIN := passt pasta qrap
+BIN := passt pasta qrap passt-repair
 endif
 
 all: $(BIN) $(MANPAGES) docs
@@ -101,6 +102,9 @@ pasta.avx2 pasta.1 pasta: pasta%: passt%
 qrap: $(QRAP_SRCS) passt.h
 	$(CC) $(FLAGS) $(CFLAGS) $(CPPFLAGS) -DARCH=\"$(TARGET_ARCH)\" $(QRAP_SRCS) -o qrap $(LDFLAGS)
 
+passt-repair: $(PASST_REPAIR_SRCS)
+	$(CC) $(FLAGS) $(CFLAGS) $(CPPFLAGS) $(PASST_REPAIR_SRCS) -o passt-repair $(LDFLAGS)
+
 valgrind: EXTRA_SYSCALLS += rt_sigprocmask rt_sigtimedwait rt_sigaction	\
 			    rt_sigreturn getpid gettid kill clock_gettime mmap \
 			    mmap2 munmap open unlink gettimeofday futex statx \
diff --git a/passt-repair.c b/passt-repair.c
new file mode 100644
index 0000000..988a52c
--- /dev/null
+++ b/passt-repair.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *  for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ *  for network namespace/tap device mode
+ *
+ * passt-repair.c - Privileged helper to set/clear TCP_REPAIR on sockets
+ *
+ * Copyright (c) 2025 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ *
+ * Connect to passt via UNIX domain socket, receive sockets via SCM_RIGHTS along
+ * with byte commands mapping to TCP_REPAIR values, and switch repair mode on or
+ * off. Reply by echoing the command. Exit on EOF.
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <unistd.h>
+#include <netdb.h>
+
+#include <netinet/tcp.h>
+
+#define SCM_MAX_FD 253 /* From Linux kernel (include/net/scm.h), not in UAPI */
+
+int main(int argc, char **argv)
+{
+	char buf[CMSG_SPACE(sizeof(int) * SCM_MAX_FD)]
+	     __attribute__ ((aligned(__alignof__(struct cmsghdr))));
+	struct sockaddr_un a = { AF_UNIX, "" };
+	int fds[SCM_MAX_FD], s, ret, i, n;
+	int8_t cmd = INT8_MAX;
+	struct cmsghdr *cmsg;
+	struct msghdr msg;
+	struct iovec iov;
+
+	iov = (struct iovec){ &cmd, sizeof(cmd) };
+	msg = (struct msghdr){ NULL, 0, &iov, 1, buf, sizeof(buf), 0 };
+	cmsg = CMSG_FIRSTHDR(&msg);
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s PATH\n", argv[0]);
+		return -1;
+	}
+
+	ret = snprintf(a.sun_path, sizeof(a.sun_path), "%s", argv[1]);
+	if (ret <= 0 || ret >= (int)sizeof(a.sun_path)) {
+		fprintf(stderr, "Invalid socket path: %s\n", argv[1]);
+		return -1;
+	}
+
+	if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
+		perror("Failed to create AF_UNIX socket");
+		return -1;
+	}
+
+	if (connect(s, (struct sockaddr *)&a, sizeof(a))) {
+		fprintf(stderr, "Failed to connect to %s: %s\n", argv[1],
+			strerror(errno));
+		return -1;
+	}
+
+loop:
+	ret = recvmsg(s, &msg, 0);
+	if (ret < 0) {
+		perror("Failed to receive message");
+		return -1;
+	}
+
+	if (!ret)	/* Done */
+		return 0;
+
+	if (!cmsg ||
+	    cmsg->cmsg_len < CMSG_LEN(sizeof(int)) ||
+	    cmsg->cmsg_len > CMSG_LEN(sizeof(int) * SCM_MAX_FD) ||
+	    cmsg->cmsg_type != SCM_RIGHTS)
+		return -1;
+
+	n = cmsg->cmsg_len / CMSG_LEN(sizeof(int));
+	memcpy(fds, CMSG_DATA(cmsg), sizeof(int) * n);
+
+	if (cmd != TCP_REPAIR_ON && cmd != TCP_REPAIR_OFF &&
+	    cmd != TCP_REPAIR_OFF_NO_WP) {
+		fprintf(stderr, "Unsupported command 0x%04x\n", cmd);
+		return -1;
+	}
+
+	for (i = 0; i < n; i++) {
+		int o = cmd;
+
+		if (setsockopt(fds[i], SOL_TCP, TCP_REPAIR, &o, sizeof(o))) {
+			fprintf(stderr,
+				"Setting TCP_REPAIR to %i on socket %i: %s", o,
+				fds[i], strerror(errno));
+			return -1;
+		}
+
+		/* Confirm setting by echoing the command back */
+		if (send(s, &cmd, sizeof(cmd), 0) < 0) {
+			fprintf(stderr, "Reply to command %i: %s\n",
+				o, strerror(errno));
+			return -1;
+		}
+	}
+
+	goto loop;
+
+	return 0;
+}
-- 
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ *  for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ *  for network namespace/tap device mode
+ *
+ * passt-repair.c - Privileged helper to set/clear TCP_REPAIR on sockets
+ *
+ * Copyright (c) 2025 Red Hat GmbH
+ * Author: Stefano Brivio <sbrivio@redhat.com>
+ *
+ * Connect to passt via UNIX domain socket, receive sockets via SCM_RIGHTS along
+ * with byte commands mapping to TCP_REPAIR values, and switch repair mode on or
+ * off. Reply by echoing the command. Exit on EOF.
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+#include <unistd.h>
+#include <netdb.h>
+
+#include <netinet/tcp.h>
+
+#define SCM_MAX_FD 253 /* From Linux kernel (include/net/scm.h), not in UAPI */
+
+int main(int argc, char **argv)
+{
+	char buf[CMSG_SPACE(sizeof(int) * SCM_MAX_FD)]
+	     __attribute__ ((aligned(__alignof__(struct cmsghdr))));
+	struct sockaddr_un a = { AF_UNIX, "" };
+	int fds[SCM_MAX_FD], s, ret, i, n;
+	int8_t cmd = INT8_MAX;
+	struct cmsghdr *cmsg;
+	struct msghdr msg;
+	struct iovec iov;
+
+	iov = (struct iovec){ &cmd, sizeof(cmd) };
+	msg = (struct msghdr){ NULL, 0, &iov, 1, buf, sizeof(buf), 0 };
+	cmsg = CMSG_FIRSTHDR(&msg);
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s PATH\n", argv[0]);
+		return -1;
+	}
+
+	ret = snprintf(a.sun_path, sizeof(a.sun_path), "%s", argv[1]);
+	if (ret <= 0 || ret >= (int)sizeof(a.sun_path)) {
+		fprintf(stderr, "Invalid socket path: %s\n", argv[1]);
+		return -1;
+	}
+
+	if ((s = socket(AF_UNIX, SOCK_STREAM, 0)) < 0) {
+		perror("Failed to create AF_UNIX socket");
+		return -1;
+	}
+
+	if (connect(s, (struct sockaddr *)&a, sizeof(a))) {
+		fprintf(stderr, "Failed to connect to %s: %s\n", argv[1],
+			strerror(errno));
+		return -1;
+	}
+
+loop:
+	ret = recvmsg(s, &msg, 0);
+	if (ret < 0) {
+		perror("Failed to receive message");
+		return -1;
+	}
+
+	if (!ret)	/* Done */
+		return 0;
+
+	if (!cmsg ||
+	    cmsg->cmsg_len < CMSG_LEN(sizeof(int)) ||
+	    cmsg->cmsg_len > CMSG_LEN(sizeof(int) * SCM_MAX_FD) ||
+	    cmsg->cmsg_type != SCM_RIGHTS)
+		return -1;
+
+	n = cmsg->cmsg_len / CMSG_LEN(sizeof(int));
+	memcpy(fds, CMSG_DATA(cmsg), sizeof(int) * n);
+
+	if (cmd != TCP_REPAIR_ON && cmd != TCP_REPAIR_OFF &&
+	    cmd != TCP_REPAIR_OFF_NO_WP) {
+		fprintf(stderr, "Unsupported command 0x%04x\n", cmd);
+		return -1;
+	}
+
+	for (i = 0; i < n; i++) {
+		int o = cmd;
+
+		if (setsockopt(fds[i], SOL_TCP, TCP_REPAIR, &o, sizeof(o))) {
+			fprintf(stderr,
+				"Setting TCP_REPAIR to %i on socket %i: %s", o,
+				fds[i], strerror(errno));
+			return -1;
+		}
+
+		/* Confirm setting by echoing the command back */
+		if (send(s, &cmd, sizeof(cmd), 0) < 0) {
+			fprintf(stderr, "Reply to command %i: %s\n",
+				o, strerror(errno));
+			return -1;
+		}
+	}
+
+	goto loop;
+
+	return 0;
+}
-- 
2.43.0