diff options
Diffstat (limited to 'passt-repair.c')
| -rw-r--r-- | passt-repair.c | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/passt-repair.c b/passt-repair.c new file mode 100644 index 0000000..767a821 --- /dev/null +++ b/passt-repair.c @@ -0,0 +1,154 @@ +// 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/prctl.h> +#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> + +#include <linux/audit.h> +#include <linux/capability.h> +#include <linux/filter.h> +#include <linux/seccomp.h> + +#include "seccomp_repair.h" + +#define SCM_MAX_FD 253 /* From Linux kernel (include/net/scm.h), not in UAPI */ + +/** + * main() - Entry point and whole program with loop + * @argc: Argument count, must be 2 + * @argv: Argument: path of UNIX domain socket to connect to + * + * Return: 0 on success (EOF), 1 on error, 2 on usage error + * + * #syscalls:repair connect setsockopt write exit_group + * #syscalls:repair socket s390x:socketcall i686:socketcall + * #syscalls:repair recvfrom recvmsg arm:recv ppc64le:recv + * #syscalls:repair sendto sendmsg arm:send ppc64le:send + */ +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; + struct sock_fprog prog; + int8_t cmd = INT8_MAX; + struct cmsghdr *cmsg; + struct msghdr msg; + struct iovec iov; + + prctl(PR_SET_DUMPABLE, 0); + + prog.len = (unsigned short)sizeof(filter_repair) / + sizeof(filter_repair[0]); + prog.filter = filter_repair; + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) || + prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) { + fprintf(stderr, "Failed to apply seccomp filter"); + return 1; + } + + 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 2; + } + + 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 2; + } + + 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) { + fprintf(stderr, "No/bad ancillary data from peer\n"); + 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; + } + + /* Close _our_ copy */ + close(fds[i]); + + /* 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; +} |