taps: MVE

- TUNSETIFF works, the interface is indeed created.
- An fd is indeed passed over the unix socket,
- and is a valid (enough) fd because it can fed into `dup2`.
- `nix run -f . --offline pkgs.taps -- pass sleep 5` works, the
  interface exists for 5 seconds and disappears
- `nix run -f . --offline pkgs.taps -- pass ch-remote --api-socket=$HOME/uvms/nixos/vmm.sock add-net fd=3`
  obscurely fails, killing the VMM with:

  ```console
  [root@nixos:~]# cloud-hypervisor:  12.388270s: <_net1_qp0> ERROR:/build/source/net_util/src/queue_pair.rs:112 -- net: tx: failed writing to tap: Input/output error (os er
  ror 5)
  cloud-hypervisor:  12.388459s: <_net1_qp0> ERROR:virtio-devices/src/thread_helper.rs:54 -- Error running worker: HandleEvent(Error processing TX queue: NetQueuePair(Write
  Tap(Os { code: 5, kind: Uncategorized, message: "Input/output error" })))
  ```

pkgs/ch-proxy/sendfd.c

@@ -36,3 +36,39 @@ ssize_t send_fd(int dst_fd, int fd, const struct iovec *iov) {
 
     return (sendmsg(dst_fd, &msg, 0));
 }
+
+int recv_fd(int sock, int flags) {
+    int out = -1;
+
+    struct msghdr msg = { 0 };
+    struct cmsghdr *cmsg = NULL;
+    struct iovec iov = { 0 };
+    char dummy = 0;
+
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+
+    iov.iov_base = &dummy;
+    iov.iov_len = sizeof(dummy);
+
+    union {
+        struct cmsghdr align;
+        char buf[CMSG_SPACE(sizeof(int))];
+    } u;
+
+    msg.msg_control = u.buf;
+    msg.msg_controllen = sizeof(u.buf);
+
+    int bytes = 0;
+    if ((bytes = recvmsg(sock, &msg, flags)) < 0) {
+        perror("recv_fd: recvmsg");
+        return -1;
+    }
+    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+        if (cmsg->cmsg_level != SOL_SOCKET) { continue; }
+        if (cmsg->cmsg_type != SCM_RIGHTS) { continue; }
+        if (CMSG_LEN(cmsg) < sizeof(out)) { continue; }
+        out = *(int*)CMSG_DATA(cmsg);
+    }
+    return out;
+}

pkgs/ch-proxy/sendfd.h

@@ -5,7 +5,23 @@
 #include <sys/types.h> /* ssize_t */
 #include <sys/uio.h> /* iovec */
 
-ssize_t send_fd(int dst_fd, int fd, const struct iovec *);
+
+/* send_fd(chanFd, fd, *iov)
+ *
+ * chanFd: fd to sendmsg over;
+ * fd: fd to send;
+ * iov: extra data to send or NULL;
+ *
+ * returns: result of sendmsg,
+ * i.e. the number of bytes sent */
+ssize_t send_fd(int chanFd, int fd, const struct iovec *);
+
+/* recv_fd(chanFd, flags)
+ *
+ * chanFd: fd to recvmsg from;
+ * flags: recvmsg flags e.g. 0, or MSG_CMSG_CLOEXEC?
+ *
+ * returns: the received fd or -1 */
+int recv_fd(int chanFd, int flags);
 
 #endif /* _CH_PROXY_SENFD */
-

pkgs/taps/main.c

@@ -10,10 +10,11 @@
 #include <pwd.h>
 #include <fnmatch.h>
 #include <fcntl.h> /* open, O_NONBLOCK, &c */
-#include <stdio.h> /* perror */
+#include <err.h>
+#include <error.h>
 #include <errno.h>
 #include <sys/ioctl.h>
-
+#include <signal.h>
 
 #define __UAPI_DEF_IF_IFNAMSIZ 1
 #include <linux/if_tun.h>
@@ -25,14 +26,19 @@
 #define SUN_PATH_SZ 108
 #define N_CONNS 16
 
-#define IFR_FLAGS_ALLOWED (IFF_NO_PI | IFF_TAP | IFF_TUN | IFF_VNET_HDR | IFF_MULTI_QUEUE)
-#define IFR_FLAGS_DEFAULT (IFF_NO_PI | IFF_TAP | IFF_VNET_HDR)
+char *TEMP_PATHS[1024] = { 0 }; 
+int LAST_TEMP_PATH = -1;
 
-#define DO_OR_DIE(expr) DO_OR_DIE_X((expr) == 0)
-#define DO_OR_DIE_X(expr) \
+#define IFR_FLAGS_ALLOWED (IFF_NO_PI | IFF_TAP | IFF_TUN | IFF_VNET_HDR | IFF_MULTI_QUEUE | IFF_PERSIST)
+#define IFR_FLAGS_DEFAULT (IFF_NO_PI | IFF_TAP | IFF_VNET_HDR | IFF_PERSIST)
+
+#define PTR_OR_DIE(expr) TRUE_OR_DIE((expr) != NULL)
+#define DO_OR_DIE(expr) TRUE_OR_DIE((expr) != -1)
+#define TRUE_OR_DIE(expr, ...) TRUE_OR_(EXIT_FAILURE, expr, __VA_ARGS__)
+#define TRUE_OR_WARN(expr, ...) TRUE_OR_(0, expr, __VA_ARGS__)
+#define TRUE_OR_(status, expr, ...) \
     do if (!(expr)) { \
-        perror((#expr)); \
-        exit(EXIT_FAILURE); \
+        error(status, errno, "Failed assertion: " #expr "." __VA_ARGS__); \
     } while(false)
 
 struct allow_pattern {
@@ -78,33 +84,29 @@ bool match_mask(const char *test_addr, const char *expected_addr, const char *ma
  *           IFF_NO_PI - Do not provide packet information
  */
 int tuntap_alloc(char *dev, short openFlags, short ifrFlags, int *out_fd) {
-  struct ifreq ifr;
-  int fd, err;
+  struct ifreq ifr = { 0 };
+  int fd = -1, err = 0;
 
-  // if ((fd = open("/dev/net/tun", O_RDWR)) < 0) {
-  //   return tun_alloc_old(dev);
-  // }
+  DO_OR_DIE(fd = open("/dev/net/tun", openFlags));
 
-  DO_OR_DIE_X((fd = open("/dev/net/tun", openFlags)) >= 0);
-
-  memset(&ifr, 0, sizeof(ifr));
-
-  if (*dev) {
+  if (dev != NULL) {
     int devLen = strlen(dev);
     if (devLen >= IFNAMSIZ) {
       /* If client requests a name, we do want the entire name to fit */
       errno = EINVAL;
       return EINVAL;
     }
-    strncpy(ifr.ifr_name, dev, IFNAMSIZ);
+    strncpy(ifr.ifr_name, dev, IFNAMSIZ - 1);
   }
+  ifr.ifr_flags = ifrFlags;
 
-  if ((err = ioctl(fd, TUNSETIFF, (void *)&ifr)) < 0) {
+  TRUE_OR_WARN((err = ioctl(fd, TUNSETIFF, (void *)&ifr)) == 0);
+  if (err != 0) {
     close(fd);
     return err;
   }
 
-  strcpy(dev, ifr.ifr_name);
+  strncpy(dev, ifr.ifr_name, IFNAMSIZ);
   *out_fd = fd;
   return 0;
 }
@@ -112,18 +114,20 @@ int tuntap_alloc(char *dev, short openFlags, short ifrFlags, int *out_fd) {
 int acceptRequests(const char *requestsPath, const struct allow_patterns *patterns) {
     int listener;
     struct sockaddr_un addr;
-    const bool t = 1;
+    const int t = 1;
 
     DO_OR_DIE(listener = socket(AF_UNIX, SOCK_SEQPACKET, 0));
-    DO_OR_DIE(setsockopt(listener, SOL_SOCKET, SO_PASSCRED, &t, 1) != 0);
+    DO_OR_DIE(setsockopt(listener, SOL_SOCKET, SO_PASSCRED, &t, sizeof(t)));
 
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, requestsPath, SUN_PATH_SZ);
-    DO_OR_DIE (bind(listener, &addr, sizeof(addr)) == -1);
+    strncpy(addr.sun_path, requestsPath, SUN_PATH_SZ - 1);
+    DO_OR_DIE (bind(listener, &addr, sizeof(addr)));
+    PTR_OR_DIE(TEMP_PATHS[++LAST_TEMP_PATH] = strdup(requestsPath));
 
     DO_OR_DIE(listen(listener, N_CONNS));
 
     for (;;) {
+        /* Already changed my mind about looking at ucred, but keeping the code around for now */
         int sock = -1;
         struct ucred cred = { 0 };
         struct msghdr msg = { 0 };
@@ -137,13 +141,14 @@ int acceptRequests(const char *requestsPath, const struct allow_patterns *patter
         iov.iov_base = &req;
         iov.iov_len = sizeof(struct tap_request);
 
-        DO_OR_DIE(sock = accept(listener, NULL, NULL));
+        DO_OR_DIE((sock = accept(listener, NULL, NULL)));
 
-        DO_OR_DIE_X(recvmsg(sock, &msg, 0) > 0);
+        TRUE_OR_DIE(recvmsg(sock, &msg, 0) > 0);
+        req.name[IFNAMSIZ] = 0;
         for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
-            if (!(cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_CREDENTIALS)) {
-                continue;
-            }
+            if (cmsg->cmsg_level != SOL_SOCKET) { continue; }
+            if (cmsg->cmsg_type != SCM_CREDENTIALS) { continue; }
+            if (CMSG_LEN(cmsg) < sizeof(struct ucred)) { continue; }
             memcpy(&cred, CMSG_DATA(cmsg), sizeof(struct ucred));
             break;
         }
@@ -163,12 +168,13 @@ int acceptRequests(const char *requestsPath, const struct allow_patterns *patter
         if (!allowed) { reply.status = AUTH_ERROR; }
         if (allowed) {
             /* O_CLOEXEC? */
-            int fd = 0;
-            DO_OR_DIE(tuntap_alloc(req.name, O_RDWR | O_NONBLOCK, req.ifrFlags, &fd));
+            int fd = -1;
+            TRUE_OR_DIE(tuntap_alloc(req.name, O_RDWR | O_NONBLOCK, req.ifrFlags, &fd) == 0);
             struct iovec iov = { 0 };
             iov.iov_base = &reply;
             iov.iov_len = sizeof(struct tap_reply);
-            DO_OR_DIE_X(send_fd(sock, fd, &iov) > 0);
+            TRUE_OR_DIE(send_fd(sock, fd, &iov) > 0);
+            close(fd); 
         }
         close(sock);
     }
@@ -186,7 +192,8 @@ struct allow_patterns parsePatterns(const char *raw) {
         if (start < i) { ++nPatterns; }
     }
 
-    struct allow_pattern *patterns = calloc(nPatterns, sizeof(struct allow_pattern));
+    struct allow_pattern *patterns = NULL;
+    PTR_OR_DIE(patterns = calloc(nPatterns, sizeof(struct allow_pattern)));
 
     int iPattern = 0;
     for (int i = 0; i < rawLen; ++i) {
@@ -195,8 +202,8 @@ struct allow_patterns parsePatterns(const char *raw) {
         {
             const int start = i;
             for (; i < rawLen && !isspace(raw[i]); ++i) { }
-            if (i < rawLen) {
-                patterns[iPattern].name = strndup(&raw[start], i - start);
+            if (start < i) {
+                PTR_OR_DIE(patterns[iPattern].name = strndup(&raw[start], i - start));
                 iPattern += 1;
             }
         }
@@ -208,34 +215,112 @@ struct allow_patterns parsePatterns(const char *raw) {
     return out;
 }
 
+int get(const char *servePath, const char *ifname, short ifrFlags) {
+    /* TODO: sock: move out */
+    int sock;
+    struct sockaddr_un addr;
+
+    DO_OR_DIE(sock = socket(AF_UNIX, SOCK_SEQPACKET, 0));
+
+    addr.sun_family = AF_UNIX;
+    strncpy(addr.sun_path, servePath, SUN_PATH_SZ - 1);
+    DO_OR_DIE (connect(sock, &addr, sizeof(addr)));
+
+    struct msghdr msg = { 0 };
+    struct cmsghdr *cmsg = NULL;
+    struct iovec iov = { 0 };
+    struct tap_request req = { 0 };
+    strncpy(req.name, ifname, IFNAMSIZ - 1);
+    req.ifrFlags = ifrFlags;
+
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+
+    iov.iov_base = &req;
+    iov.iov_len = sizeof(struct tap_request);
+
+    TRUE_OR_DIE(sendmsg(sock, &msg, 0) > 0);
+
+    int tunFd = -1;
+    DO_OR_DIE(tunFd = recv_fd(sock, 0));
+    close(sock);
+    return tunFd;
+}
+
+void cleanup(int signo, siginfo_t *info, void *_context) {
+    for (int i = 0; i <= LAST_TEMP_PATH; ++i) {
+        TRUE_OR_DIE(unlink(TEMP_PATHS[i]) != -1 || errno == ENOENT);
+    }
+    if (signo == SIGINT) {
+        exit(EXIT_SUCCESS);
+    }
+    errx(EXIT_FAILURE, "Exiting with signal %d", signo);
+}
+
 int main(int argc, char **argv) {
+    struct sigaction act = { 0 };
+    act.sa_flags = SA_SIGINFO;
+    act.sa_sigaction = cleanup;
+    DO_OR_DIE(sigaction(SIGINT, &act, NULL));
+    DO_OR_DIE(sigaction(SIGSEGV, &act, NULL));
+
     bool cmdServe = false;
-    bool cmdGet = false;
+    bool cmdPass = false;
+    char *ifname = "vt%d";
 
     char **rest = argv + 1;
+    char **end = argv + argc;
 
+    TRUE_OR_DIE(argc > 1);
     if (strcmp(rest[0], "serve") == 0) {
         cmdServe = true;
         ++rest;
-    } else if (strcmp(rest[0], "get") == 0) {
-        cmdGet = true;
+    } else if (strcmp(rest[0], "pass") == 0) {
+        cmdPass = true;
         ++rest;
+        for (; rest != end && rest[0][0] == '-'; ++rest) {
+            if (strcmp(rest[0], "--")) { break; }
+            else if (strncmp(rest[0], "--ifname=", sizeof("--ifname="))) {
+                ifname = rest[0] + sizeof("--ifname=");
+            }
+        }
     } else {
-        exit(EXIT_FAILURE);
+        error(EINVAL, EINVAL, "no subcommand \"%s\"", rest[0]);
     }
 
+    int nextArgc = argc - (rest - argv);
+    char * const* nextArgv = rest;
+
     const char *patternsRaw = secure_getenv("TAPS_ALLOW");
+    if (patternsRaw == NULL) {
+        patternsRaw = "*";
+    }
+
     struct allow_patterns patterns = { 0 };
-    if (cmdServe && patternsRaw != NULL) { patterns = parsePatterns(patternsRaw); }
-    DO_OR_DIE_X(patterns.patterns != NULL);
+    if (cmdServe) {
+        PTR_OR_DIE((patterns = parsePatterns(patternsRaw)).patterns);
+    }
 
     const char *servePath = secure_getenv("TAPS_SOCK");
+    if (servePath == NULL) {
+        servePath = "taps.sock";
+    }
 
-    if (cmdServe && patterns.patterns != NULL) {
+    if (cmdServe) {
         acceptRequests(servePath, &patterns);
-    } else if (cmdGet) {
+    } else if (cmdPass) {
+        TRUE_OR_DIE(nextArgc > 0);
+        int fd = -1;
+        DO_OR_DIE(fd = get(servePath, ifname, 0));
+        if (fd != 3) {
+            DO_OR_DIE(dup2(fd, 3));
+            close(fd);
+            fd = 3;
+        }
+        DO_OR_DIE(execvp(nextArgv[0], nextArgv));
     } else {
-        exit(EXIT_FAILURE); }
+        error(EINVAL, EINVAL, "subcommand args");
+    }
 
     return 0;
 }

shell.nix

@@ -6,5 +6,8 @@ mkShell.override { stdenv = stdenvNoCC; } {
     virtiofsd
     crosvm # virtio-gpu
     npins
+  ] ++ [
+    man-pages
+    linux-manual
   ];
 }