afs: fix sget() races, close leak on umount

* set ->s_fs_info in set() callback passed to sget()
* allocate the thing and set it up enough for afs_test_super() before
making it visible
* have it freed in ->kill_sb() (current tree simply leaks it)
* have ->put_super() leave ->s_fs_info->volume alone; it's too early for
dropping it; do that from ->kill_sb() after having called kill_anon_super().

Signed-off-by: Al Viro <[e-mail]>

fs/afs/super.c

···
 static void afs_i_init_once(void *foo);
 static struct dentry *afs_mount(struct file_system_type *fs_type,
 		      int flags, const char *dev_name, void *data);
+static void afs_kill_super(struct super_block *sb);
 static struct inode *afs_alloc_inode(struct super_block *sb);
-static void afs_put_super(struct super_block *sb);
 static void afs_destroy_inode(struct inode *inode);
 static int afs_statfs(struct dentry *dentry, struct kstatfs *buf);
 
···
 	.owner		= THIS_MODULE,
 	.name		= "afs",
 	.mount		= afs_mount,
-	.kill_sb	= kill_anon_super,
+	.kill_sb	= afs_kill_super,
 	.fs_flags	= 0,
 };
 
···
 	.drop_inode	= afs_drop_inode,
 	.destroy_inode	= afs_destroy_inode,
 	.evict_inode	= afs_evict_inode,
-	.put_super	= afs_put_super,
 	.show_options	= generic_show_options,
 };
 
···
  */
 static int afs_test_super(struct super_block *sb, void *data)
 {
-	struct afs_mount_params *params = data;
+	struct afs_super_info *as1 = data;
 	struct afs_super_info *as = sb->s_fs_info;
 
-	return as->volume == params->volume;
+	return as->volume == as1->volume;
+}
+
+static int afs_set_super(struct super_block *sb, void *data)
+{
+	sb->s_fs_info = data;
+	return set_anon_super(sb, NULL);
 }
 
 /*
  * fill in the superblock
  */
-static int afs_fill_super(struct super_block *sb, void *data)
+static int afs_fill_super(struct super_block *sb,
+			  struct afs_mount_params *params)
 {
-	struct afs_mount_params *params = data;
-	struct afs_super_info *as = NULL;
+	struct afs_super_info *as = sb->s_fs_info;
 	struct afs_fid fid;
 	struct dentry *root = NULL;
 	struct inode *inode = NULL;
···
 
 	_enter("");
 
-	/* allocate a superblock info record */
-	as = kzalloc(sizeof(struct afs_super_info), GFP_KERNEL);
-	if (!as) {
-		_leave(" = -ENOMEM");
-		return -ENOMEM;
-	}
-
-	afs_get_volume(params->volume);
-	as->volume = params->volume;
-
 	/* fill in the superblock */
 	sb->s_blocksize		= PAGE_CACHE_SIZE;
 	sb->s_blocksize_bits	= PAGE_CACHE_SHIFT;
 	sb->s_magic		= AFS_FS_MAGIC;
 	sb->s_op		= &afs_super_ops;
-	sb->s_fs_info		= as;
 	sb->s_bdi		= &as->volume->bdi;
 
 	/* allocate the root inode and dentry */
···
 	fid.unique	= 1;
 	inode = afs_iget(sb, params->key, &fid, NULL, NULL);
 	if (IS_ERR(inode))
-		goto error_inode;
+		return PTR_ERR(inode);
 
 	if (params->autocell)
 		set_bit(AFS_VNODE_AUTOCELL, &AFS_FS_I(inode)->flags);
···
 	_leave(" = 0");
 	return 0;
 
-error_inode:
-	ret = PTR_ERR(inode);
-	inode = NULL;
 error:
 	iput(inode);
-	afs_put_volume(as->volume);
-	kfree(as);
-
-	sb->s_fs_info = NULL;
-
 	_leave(" = %d", ret);
 	return ret;
 }
···
 	struct afs_volume *vol;
 	struct key *key;
 	char *new_opts = kstrdup(options, GFP_KERNEL);
+	struct afs_super_info *as;
 	int ret;
 
 	_enter(",,%s,%p", dev_name, options);
···
 		ret = PTR_ERR(vol);
 		goto error;
 	}
-	params.volume = vol;
+
+	/* allocate a superblock info record */
+	as = kzalloc(sizeof(struct afs_super_info), GFP_KERNEL);
+	if (!as) {
+		ret = -ENOMEM;
+		afs_put_volume(vol);
+		goto error;
+	}
+	as->volume = vol;
 
 	/* allocate a deviceless superblock */
-	sb = sget(fs_type, afs_test_super, set_anon_super, &params);
+	sb = sget(fs_type, afs_test_super, afs_set_super, as);
 	if (IS_ERR(sb)) {
 		ret = PTR_ERR(sb);
+		afs_put_volume(vol);
+		kfree(as);
 		goto error;
 	}
 
···
 	} else {
 		_debug("reuse");
 		ASSERTCMP(sb->s_flags, &, MS_ACTIVE);
+		afs_put_volume(vol);
+		kfree(as);
 	}
 
-	afs_put_volume(params.volume);
 	afs_put_cell(params.cell);
 	kfree(new_opts);
 	_leave(" = 0 [%p]", sb);
 	return dget(sb->s_root);
 
 error:
-	afs_put_volume(params.volume);
 	afs_put_cell(params.cell);
 	key_put(params.key);
 	kfree(new_opts);
···
 	return ERR_PTR(ret);
 }
 
-/*
- * finish the unmounting process on the superblock
- */
-static void afs_put_super(struct super_block *sb)
+static void afs_kill_super(struct super_block *sb)
 {
 	struct afs_super_info *as = sb->s_fs_info;
-
-	_enter("");
-
+	kill_anon_super(sb);
 	afs_put_volume(as->volume);
-
-	_leave("");
+	kfree(as);
 }
 
 /*