From: Stefan Hajnoczi <stefa...@redhat.com>

fuse_fill_super() includes code to process the fd= option and link the
struct fuse_dev to the fd's struct file.  In virtio-fs there is no file
descriptor because /dev/fuse is not used.

This patch extracts fuse_fill_super_common() so that both classic fuse
and virtio-fs can share the code to initialize a mount.

parse_fuse_opt() is also extracted so that the fuse_fill_super_common()
caller has access to the mount options.  This allows classic fuse to
handle the fd= option outside fuse_fill_super_common().

Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Signed-off-by: Miklos Szeredi <mszer...@redhat.com>
---
 fs/fuse/fuse_i.h |  33 ++++++++++++
 fs/fuse/inode.c  | 137 ++++++++++++++++++++++++-----------------------
 2 files changed, 103 insertions(+), 67 deletions(-)

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 38a572ba650d..84f094e4ac36 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -56,6 +56,25 @@ extern struct mutex fuse_mutex;
 extern unsigned max_user_bgreq;
 extern unsigned max_user_congthresh;
 
+/** Mount options */
+struct fuse_mount_data {
+       int fd;
+       unsigned rootmode;
+       kuid_t user_id;
+       kgid_t group_id;
+       unsigned fd_present:1;
+       unsigned rootmode_present:1;
+       unsigned user_id_present:1;
+       unsigned group_id_present:1;
+       unsigned default_permissions:1;
+       unsigned allow_other:1;
+       unsigned max_read;
+       unsigned blksize;
+
+       /* fuse_dev pointer to fill in, should contain NULL on entry */
+       void **fudptr;
+};
+
 /* One forget request */
 struct fuse_forget_link {
        struct fuse_forget_one forget_one;
@@ -989,6 +1008,20 @@ struct fuse_dev *fuse_dev_alloc(struct fuse_conn *fc);
 void fuse_dev_free(struct fuse_dev *fud);
 void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req);
 
+/**
+ * Parse a mount options string
+ */
+int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
+                               struct user_namespace *user_ns);
+
+/**
+ * Fill in superblock and initialize fuse connection
+ * @sb: partially-initialized superblock to fill in
+ * @mount_data: mount parameters
+ */
+int fuse_fill_super_common(struct super_block *sb,
+                          struct fuse_mount_data *mount_data);
+
 /**
  * Add connection to control filesystem
  */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index f02291469518..baf2966a753a 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -59,21 +59,6 @@ MODULE_PARM_DESC(max_user_congthresh,
 /** Congestion starts at 75% of maximum */
 #define FUSE_DEFAULT_CONGESTION_THRESHOLD (FUSE_DEFAULT_MAX_BACKGROUND * 3 / 4)
 
-struct fuse_mount_data {
-       int fd;
-       unsigned rootmode;
-       kuid_t user_id;
-       kgid_t group_id;
-       unsigned fd_present:1;
-       unsigned rootmode_present:1;
-       unsigned user_id_present:1;
-       unsigned group_id_present:1;
-       unsigned default_permissions:1;
-       unsigned allow_other:1;
-       unsigned max_read;
-       unsigned blksize;
-};
-
 struct fuse_forget_link *fuse_alloc_forget(void)
 {
        return kzalloc(sizeof(struct fuse_forget_link), GFP_KERNEL);
@@ -482,7 +467,7 @@ static int fuse_match_uint(substring_t *s, unsigned int 
*res)
        return err;
 }
 
-static int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
+int parse_fuse_opt(char *opt, struct fuse_mount_data *d, int is_bdev,
                          struct user_namespace *user_ns)
 {
        char *p;
@@ -559,12 +544,13 @@ static int parse_fuse_opt(char *opt, struct 
fuse_mount_data *d, int is_bdev,
                }
        }
 
-       if (!d->fd_present || !d->rootmode_present ||
-           !d->user_id_present || !d->group_id_present)
+       if (!d->rootmode_present || !d->user_id_present ||
+           !d->group_id_present)
                return 0;
 
        return 1;
 }
+EXPORT_SYMBOL_GPL(parse_fuse_opt);
 
 static int fuse_show_options(struct seq_file *m, struct dentry *root)
 {
@@ -1079,15 +1065,13 @@ void fuse_dev_free(struct fuse_dev *fud)
 }
 EXPORT_SYMBOL_GPL(fuse_dev_free);
 
-static int fuse_fill_super(struct super_block *sb, void *data, int silent)
+int fuse_fill_super_common(struct super_block *sb,
+                          struct fuse_mount_data *mount_data)
 {
        struct fuse_dev *fud;
        struct fuse_conn *fc;
        struct inode *root;
-       struct fuse_mount_data d;
-       struct file *file;
        struct dentry *root_dentry;
-       struct fuse_req *init_req;
        int err;
        int is_bdev = sb->s_bdev != NULL;
 
@@ -1097,13 +1081,10 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
 
        sb->s_flags &= ~(SB_NOSEC | SB_I_VERSION);
 
-       if (!parse_fuse_opt(data, &d, is_bdev, sb->s_user_ns))
-               goto err;
-
        if (is_bdev) {
 #ifdef CONFIG_BLOCK
                err = -EINVAL;
-               if (!sb_set_blocksize(sb, d.blksize))
+               if (!sb_set_blocksize(sb, mount_data->blksize))
                        goto err;
 #endif
        } else {
@@ -1120,19 +1101,6 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
        if (sb->s_user_ns != &init_user_ns)
                sb->s_iflags |= SB_I_UNTRUSTED_MOUNTER;
 
-       file = fget(d.fd);
-       err = -EINVAL;
-       if (!file)
-               goto err;
-
-       /*
-        * Require mount to happen from the same user namespace which
-        * opened /dev/fuse to prevent potential attacks.
-        */
-       if (file->f_op != &fuse_dev_operations ||
-           file->f_cred->user_ns != sb->s_user_ns)
-               goto err_fput;
-
        /*
         * If we are not in the initial user namespace posix
         * acls must be translated.
@@ -1143,7 +1111,7 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
        fc = kmalloc(sizeof(*fc), GFP_KERNEL);
        err = -ENOMEM;
        if (!fc)
-               goto err_fput;
+               goto err;
 
        fuse_conn_init(fc, sb->s_user_ns);
        fc->release = fuse_free_conn;
@@ -1163,17 +1131,17 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
                fc->dont_mask = 1;
        sb->s_flags |= SB_POSIXACL;
 
-       fc->default_permissions = d.default_permissions;
-       fc->allow_other = d.allow_other;
-       fc->user_id = d.user_id;
-       fc->group_id = d.group_id;
-       fc->max_read = max_t(unsigned, 4096, d.max_read);
+       fc->default_permissions = mount_data->default_permissions;
+       fc->allow_other = mount_data->allow_other;
+       fc->user_id = mount_data->user_id;
+       fc->group_id = mount_data->group_id;
+       fc->max_read = max_t(unsigned, 4096, mount_data->max_read);
 
        /* Used by get_root_inode() */
        sb->s_fs_info = fc;
 
        err = -ENOMEM;
-       root = fuse_get_root_inode(sb, d.rootmode);
+       root = fuse_get_root_inode(sb, mount_data->rootmode);
        sb->s_d_op = &fuse_root_dentry_operations;
        root_dentry = d_make_root(root);
        if (!root_dentry)
@@ -1181,20 +1149,15 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
        /* Root dentry doesn't have .d_revalidate */
        sb->s_d_op = &fuse_dentry_operations;
 
-       init_req = fuse_request_alloc(0);
-       if (!init_req)
-               goto err_put_root;
-       __set_bit(FR_BACKGROUND, &init_req->flags);
-
        if (is_bdev) {
                fc->destroy_req = fuse_request_alloc(0);
                if (!fc->destroy_req)
-                       goto err_free_init_req;
+                       goto err_put_root;
        }
 
        mutex_lock(&fuse_mutex);
        err = -EINVAL;
-       if (file->private_data)
+       if (*mount_data->fudptr)
                goto err_unlock;
 
        err = fuse_ctl_add_conn(fc);
@@ -1203,23 +1166,12 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
 
        list_add_tail(&fc->entry, &fuse_conn_list);
        sb->s_root = root_dentry;
-       file->private_data = fud;
+       *mount_data->fudptr = fud;
        mutex_unlock(&fuse_mutex);
-       /*
-        * atomic_dec_and_test() in fput() provides the necessary
-        * memory barrier for file->private_data to be visible on all
-        * CPUs after this
-        */
-       fput(file);
-
-       fuse_send_init(fc, init_req);
-
        return 0;
 
  err_unlock:
        mutex_unlock(&fuse_mutex);
- err_free_init_req:
-       fuse_request_free(init_req);
  err_put_root:
        dput(root_dentry);
  err_dev_free:
@@ -1227,11 +1179,62 @@ static int fuse_fill_super(struct super_block *sb, void 
*data, int silent)
  err_put_conn:
        fuse_conn_put(fc);
        sb->s_fs_info = NULL;
- err_fput:
-       fput(file);
  err:
        return err;
 }
+EXPORT_SYMBOL_GPL(fuse_fill_super_common);
+
+static int fuse_fill_super(struct super_block *sb, void *data, int silent)
+{
+       struct fuse_mount_data d;
+       struct file *file;
+       int is_bdev = sb->s_bdev != NULL;
+       int err;
+       struct fuse_req *init_req;
+
+       err = -EINVAL;
+       if (!parse_fuse_opt(data, &d, is_bdev, sb->s_user_ns))
+               goto err;
+       if (!d.fd_present)
+               goto err;
+
+       file = fget(d.fd);
+       if (!file)
+               goto err;
+
+       /*
+        * Require mount to happen from the same user namespace which
+        * opened /dev/fuse to prevent potential attacks.
+        */
+       if ((file->f_op != &fuse_dev_operations) ||
+           (file->f_cred->user_ns != sb->s_user_ns))
+               goto err_fput;
+
+       init_req = fuse_request_alloc(0);
+       if (!init_req)
+               goto err_fput;
+       __set_bit(FR_BACKGROUND, &init_req->flags);
+
+       d.fudptr = &file->private_data;
+       err = fuse_fill_super_common(sb, &d);
+       if (err < 0)
+               goto err_free_init_req;
+       /*
+        * atomic_dec_and_test() in fput() provides the necessary
+        * memory barrier for file->private_data to be visible on all
+        * CPUs after this
+        */
+       fput(file);
+       fuse_send_init(get_fuse_conn_super(sb), init_req);
+       return 0;
+
+err_free_init_req:
+       fuse_request_free(init_req);
+err_fput:
+       fput(file);
+err:
+       return err;
+}
 
 static struct dentry *fuse_mount(struct file_system_type *fs_type,
                       int flags, const char *dev_name,
-- 
2.20.1

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