[RFC PATCH] tools/virtiofsd: add support for --socket-group

["Alex Bennée" <alex.bennee@linaro.org>]

If you like running QEMU as a normal user (very common for TCG runs)
but you have to run virtiofsd as a root user you run into connection
problems. Adding support for an optional --socket-group allows the
users to keep using the command line.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 docs/tools/virtiofsd.rst        |  4 ++++
 tools/virtiofsd/fuse_i.h        |  1 +
 tools/virtiofsd/fuse_lowlevel.c |  6 ++++++
 tools/virtiofsd/fuse_virtio.c   | 20 ++++++++++++++++++--
 4 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
index 378594c422a..6d2342f74d4 100644
--- a/docs/tools/virtiofsd.rst
+++ b/docs/tools/virtiofsd.rst
@@ -85,6 +85,10 @@ Options
 
   Listen on vhost-user UNIX domain socket at PATH.
 
+.. option:: --socket-group=GROUP
+
+  Also make vhost-user UNIX domain socket accessible to GROUP.
+
 .. option:: --fd=FDNUM
 
   Accept connections from vhost-user UNIX domain socket file descriptor FDNUM.
diff --git a/tools/virtiofsd/fuse_i.h b/tools/virtiofsd/fuse_i.h
index 1240828208a..492e002181e 100644
--- a/tools/virtiofsd/fuse_i.h
+++ b/tools/virtiofsd/fuse_i.h
@@ -68,6 +68,7 @@ struct fuse_session {
     size_t bufsize;
     int error;
     char *vu_socket_path;
+    char *vu_socket_group;
     int   vu_listen_fd;
     int   vu_socketfd;
     struct fv_VuDev *virtio_dev;
diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
index 2dd36ec03b6..4d1ba2925d1 100644
--- a/tools/virtiofsd/fuse_lowlevel.c
+++ b/tools/virtiofsd/fuse_lowlevel.c
@@ -2523,6 +2523,7 @@ static const struct fuse_opt fuse_ll_opts[] = {
     LL_OPTION("--debug", debug, 1),
     LL_OPTION("allow_root", deny_others, 1),
     LL_OPTION("--socket-path=%s", vu_socket_path, 0),
+    LL_OPTION("--socket-group=%s", vu_socket_group, 0),
     LL_OPTION("--fd=%d", vu_listen_fd, 0),
     LL_OPTION("--thread-pool-size=%d", thread_pool_size, 0),
     FUSE_OPT_END
@@ -2630,6 +2631,11 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,
                  "fuse: --socket-path and --fd cannot be given together\n");
         goto out4;
     }
+    if (se->vu_socket_group && !se->vu_socket_path) {
+        fuse_log(FUSE_LOG_ERR,
+                 "fuse: --socket-group can only be used with --socket-path\n");
+        goto out4;
+    }
 
     se->bufsize = FUSE_MAX_MAX_PAGES * getpagesize() + FUSE_BUFFER_HEADER_SIZE;
 
diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
index 3b6d16a0417..13d69525646 100644
--- a/tools/virtiofsd/fuse_virtio.c
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -31,6 +31,8 @@
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
+#include <sys/types.h>
+#include <grp.h>
 #include <unistd.h>
 
 #include "contrib/libvhost-user/libvhost-user.h"
@@ -924,15 +926,29 @@ static int fv_create_listen_socket(struct fuse_session *se)
 
     /*
      * Unfortunately bind doesn't let you set the mask on the socket,
-     * so set umask to 077 and restore it later.
+     * so set umask to appropriately and restore it later.
      */
-    old_umask = umask(0077);
+    if (se->vu_socket_group) {
+        old_umask = umask(S_IROTH | S_IWOTH | S_IXOTH);
+    } else {
+        old_umask = umask(S_IRGRP | S_IWGRP | S_IXGRP | S_IROTH | S_IWOTH | S_IXOTH);
+    }
     if (bind(listen_sock, (struct sockaddr *)&un, addr_len) == -1) {
         fuse_log(FUSE_LOG_ERR, "vhost socket bind: %m\n");
         close(listen_sock);
         umask(old_umask);
         return -1;
     }
+    if (se->vu_socket_group) {
+        struct group *g = getgrnam(se->vu_socket_group);
+        if (g) {
+            if (!chown(se->vu_socket_path, -1, g->gr_gid)) {
+                fuse_log(FUSE_LOG_WARNING,
+                         "vhost socket failed to set group to %s (%d)\n",
+                         se->vu_socket_group, g->gr_gid);
+            }
+        }
+    }
     umask(old_umask);
 
     if (listen(listen_sock, 1) == -1) {
-- 
2.20.1