9pfs: local: Add support for custom fmode/dmode in 9ps mapped security modes

In mapped security modes, files are created with very restrictive
permissions (600 for files and 700 for directories). This makes
file sharing between virtual machines and users on the host rather
complicated. Imagine eg. a group of users that need to access data
produced by processes on a virtual machine. Giving those users access
to the data will be difficult since the group access mode is always 0.

This patch makes the default mode for both files and directories
configurable. Existing setups that don't know about the new parameters
keep using the current secure behavior.

Signed-off-by: Tobias Schramm <tobleminer@gmail.com>
Signed-off-by: Greg Kurz <groug@kaod.org>

fsdev/file-op-9p.h

@@ -76,6 +76,8 @@ typedef struct FsDriverEntry {
     int export_flags;
     FileOperations *ops;
     FsThrottle fst;
+    mode_t fmode;
+    mode_t dmode;
 } FsDriverEntry;
 
 typedef struct FsContext
@@ -88,6 +90,8 @@ typedef struct FsContext
     FsThrottle *fst;
     /* fs driver specific data */
     void *private;
+    mode_t fmode;
+    mode_t dmode;
 } FsContext;
 
 typedef struct V9fsPath {

fsdev/qemu-fsdev-opts.c

@@ -38,6 +38,12 @@ static QemuOptsList qemu_fsdev_opts = {
         }, {
             .name = "sock_fd",
             .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "fmode",
+            .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "dmode",
+            .type = QEMU_OPT_NUMBER,
         },
 
         THROTTLE_OPTS,
@@ -75,6 +81,12 @@ static QemuOptsList qemu_virtfs_opts = {
         }, {
             .name = "sock_fd",
             .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "fmode",
+            .type = QEMU_OPT_NUMBER,
+        }, {
+            .name = "dmode",
+            .type = QEMU_OPT_NUMBER,
         },
 
         { /*End of list */ }

hw/9pfs/9p-local.c

@@ -633,7 +633,7 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path,
 
     if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
         fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
-        err = mknodat(dirfd, name, SM_LOCAL_MODE_BITS | S_IFREG, 0);
+        err = mknodat(dirfd, name, fs_ctx->fmode | S_IFREG, 0);
         if (err == -1) {
             goto out;
         }
@@ -685,7 +685,7 @@ static int local_mkdir(FsContext *fs_ctx, V9fsPath *dir_path,
 
     if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
         fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
-        err = mkdirat(dirfd, name, SM_LOCAL_DIR_MODE_BITS);
+        err = mkdirat(dirfd, name, fs_ctx->dmode);
         if (err == -1) {
             goto out;
         }
@@ -786,7 +786,7 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name,
     /* Determine the security model */
     if (fs_ctx->export_flags & V9FS_SM_MAPPED ||
         fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
-        fd = openat_file(dirfd, name, flags, SM_LOCAL_MODE_BITS);
+        fd = openat_file(dirfd, name, flags, fs_ctx->fmode);
         if (fd == -1) {
             goto out;
         }
@@ -849,7 +849,7 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath,
         ssize_t oldpath_size, write_size;
 
         fd = openat_file(dirfd, name, O_CREAT | O_EXCL | O_RDWR,
-                         SM_LOCAL_MODE_BITS);
+                         fs_ctx->fmode);
         if (fd == -1) {
             goto out;
         }
@@ -1467,6 +1467,23 @@ static int local_parse_opts(QemuOpts *opts, struct FsDriverEntry *fse)
         return -1;
     }
 
+    if (fse->export_flags & V9FS_SM_MAPPED ||
+        fse->export_flags & V9FS_SM_MAPPED_FILE) {
+        fse->fmode =
+            qemu_opt_get_number(opts, "fmode", SM_LOCAL_MODE_BITS) & 0777;
+        fse->dmode =
+            qemu_opt_get_number(opts, "dmode", SM_LOCAL_DIR_MODE_BITS) & 0777;
+    } else {
+        if (qemu_opt_find(opts, "fmode")) {
+            error_report("fmode is only valid for mapped 9p modes");
+            return -1;
+        }
+        if (qemu_opt_find(opts, "dmode")) {
+            error_report("dmode is only valid for mapped 9p modes");
+            return -1;
+        }
+    }
+
     fse->path = g_strdup(path);
 
     return 0;

hw/9pfs/9p.c

@@ -3533,6 +3533,9 @@ int v9fs_device_realize_common(V9fsState *s, Error **errp)
 
     s->ops = fse->ops;
 
+    s->ctx.fmode = fse->fmode;
+    s->ctx.dmode = fse->dmode;
+
     s->fid_list = NULL;
     qemu_co_rwlock_init(&s->rename_lock);
 

qemu-options.hx

@@ -1010,7 +1010,7 @@ ETEXI
 
 DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
     "-fsdev fsdriver,id=id[,path=path,][security_model={mapped-xattr|mapped-file|passthrough|none}]\n"
-    " [,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd]\n"
+    " [,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd][,fmode=fmode][,dmode=dmode]\n"
     " [[,throttling.bps-total=b]|[[,throttling.bps-read=r][,throttling.bps-write=w]]]\n"
     " [[,throttling.iops-total=i]|[[,throttling.iops-read=r][,throttling.iops-write=w]]]\n"
     " [[,throttling.bps-total-max=bm]|[[,throttling.bps-read-max=rm][,throttling.bps-write-max=wm]]]\n"
@@ -1020,7 +1020,7 @@ DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
 
 STEXI
 
-@item -fsdev @var{fsdriver},id=@var{id},path=@var{path},[security_model=@var{security_model}][,writeout=@var{writeout}][,readonly][,socket=@var{socket}|sock_fd=@var{sock_fd}]
+@item -fsdev @var{fsdriver},id=@var{id},path=@var{path},[security_model=@var{security_model}][,writeout=@var{writeout}][,readonly][,socket=@var{socket}|sock_fd=@var{sock_fd}][,fmode=@var{fmode}][,dmode=@var{dmode}]
 @findex -fsdev
 Define a new file system device. Valid options are:
 @table @option
@@ -1061,6 +1061,12 @@ with virtfs-proxy-helper
 Enables proxy filesystem driver to use passed socket descriptor for
 communicating with virtfs-proxy-helper. Usually a helper like libvirt
 will create socketpair and pass one of the fds as sock_fd
+@item fmode=@var{fmode}
+Specifies the default mode for newly created files on the host. Works only
+with security models "mapped-xattr" and "mapped-file".
+@item dmode=@var{dmode}
+Specifies the default mode for newly created directories on the host. Works
+only with security models "mapped-xattr" and "mapped-file".
 @end table
 
 -fsdev option is used along with -device driver "virtio-9p-pci".
@@ -1077,12 +1083,12 @@ ETEXI
 
 DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
     "-virtfs local,path=path,mount_tag=tag,security_model=[mapped-xattr|mapped-file|passthrough|none]\n"
-    "        [,id=id][,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd]\n",
+    "        [,id=id][,writeout=immediate][,readonly][,socket=socket|sock_fd=sock_fd][,fmode=fmode][,dmode=dmode]\n",
     QEMU_ARCH_ALL)
 
 STEXI
 
-@item -virtfs @var{fsdriver}[,path=@var{path}],mount_tag=@var{mount_tag}[,security_model=@var{security_model}][,writeout=@var{writeout}][,readonly][,socket=@var{socket}|sock_fd=@var{sock_fd}]
+@item -virtfs @var{fsdriver}[,path=@var{path}],mount_tag=@var{mount_tag}[,security_model=@var{security_model}][,writeout=@var{writeout}][,readonly][,socket=@var{socket}|sock_fd=@var{sock_fd}][,fmode=@var{fmode}][,dmode=@var{dmode}]
 @findex -virtfs
 
 The general form of a Virtual File system pass-through options are:
@@ -1124,6 +1130,12 @@ will create socketpair and pass one of the fds as sock_fd
 @item sock_fd
 Enables proxy filesystem driver to use passed 'sock_fd' as the socket
 descriptor for interfacing with virtfs-proxy-helper
+@item fmode=@var{fmode}
+Specifies the default mode for newly created files on the host. Works only
+with security models "mapped-xattr" and "mapped-file".
+@item dmode=@var{dmode}
+Specifies the default mode for newly created directories on the host. Works
+only with security models "mapped-xattr" and "mapped-file".
 @end table
 ETEXI