virtio-9p: Security model for chown

mapped model changes the owner in the extended attributes.
passthrough model does the change through lchown() as the
server don't need to follow the link and client will send the
actual filesystem object.
Signed-off-by: NVenkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/file-op-9p.h

@@ -50,7 +50,7 @@ typedef struct FileOperations
     int (*lstat)(FsContext *, const char *, struct stat *);
     ssize_t (*readlink)(FsContext *, const char *, char *, size_t);
     int (*chmod)(FsContext *, const char *, FsCred *);
-    int (*chown)(FsContext *, const char *, uid_t, gid_t);
+    int (*chown)(FsContext *, const char *, FsCred *);
     int (*mknod)(FsContext *, const char *, mode_t, dev_t);
     int (*mksock)(FsContext *, const char *);
     int (*utime)(FsContext *, const char *, const struct utimbuf *);

hw/virtio-9p-local.c

@@ -240,9 +240,14 @@ static int local_rename(FsContext *ctx, const char *oldpath,
 
 }
 
-static int local_chown(FsContext *ctx, const char *path, uid_t uid, gid_t gid)
+static int local_chown(FsContext *fs_ctx, const char *path, FsCred *credp)
 {
-    return chown(rpath(ctx, path), uid, gid);
+    if (fs_ctx->fs_sm == SM_MAPPED) {
+        return local_set_xattr(rpath(fs_ctx, path), credp);
+    } else if (fs_ctx->fs_sm == SM_PASSTHROUGH) {
+        return lchown(rpath(fs_ctx, path), credp->fc_uid, credp->fc_gid);
+    }
+    return -1;
 }
 
 static int local_utime(FsContext *ctx, const char *path,

hw/virtio-9p.c

@@ -209,7 +209,12 @@ static int v9fs_do_rename(V9fsState *s, V9fsString *oldpath,
 
 static int v9fs_do_chown(V9fsState *s, V9fsString *path, uid_t uid, gid_t gid)
 {
-    return s->ops->chown(&s->ctx, path->data, uid, gid);
+    FsCred cred;
+    cred_init(&cred);
+    cred.fc_uid = uid;
+    cred.fc_gid = gid;
+
+    return s->ops->chown(&s->ctx, path->data, &cred);
 }
 
 static int v9fs_do_utime(V9fsState *s, V9fsString *path,
@@ -2014,7 +2019,7 @@ static void v9fs_wstat_post_utime(V9fsState *s, V9fsWstatState *vs, int err)
         goto out;
     }
 
-    if (vs->v9stat.n_gid != -1) {
+    if (vs->v9stat.n_gid != -1 || vs->v9stat.n_uid != -1) {
         if (v9fs_do_chown(s, &vs->fidp->path, vs->v9stat.n_uid,
                     vs->v9stat.n_gid)) {
             err = -errno;