linux-kernel - Re: [PATCH] fuse: Ensure posix acls are translated outside of init_user

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Date:   Wed, 23 May 2018 11:11:24 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Miklos Szeredi <mszeredi@...hat.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alban Crequy <alban@...volk.io>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Dongsu Park <dongsu@...volk.io>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH] fuse: Ensure posix acls are translated outside of init_user_ns

ebiederm@...ssion.com (Eric W. Biederman) writes:

> Ensure the translation happens by failing to read or write
> posix acls when the filesystem has not indicated it supports
> posix acls.
>
> This ensures that modern cached posix acl support is available
> and used when dealing with posix acls.  This is important
> because only that path has the code to convernt the uids and
> gids in posix acls into the user namespace of a fuse filesystem.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---

ping.

Miklos are you around where you can look at this?

> Miklos after several attempts to handle this better last cycle.  I
> figure we should go with the stupid version for now.  I think I know
> how to do better but I don't want that to gate forward progress on
> fully unprivileged fuse mounts.  Especially as this is the last known
> issue to deal with.
>
>  fs/fuse/fuse_i.h |  1 +
>  fs/fuse/inode.c  |  7 +++++++
>  fs/fuse/xattr.c  | 43 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 51 insertions(+)
>
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index f630951df8dc..5256ad333b05 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -985,6 +985,7 @@ ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size);
>  int fuse_removexattr(struct inode *inode, const char *name);
>  extern const struct xattr_handler *fuse_xattr_handlers[];
>  extern const struct xattr_handler *fuse_acl_xattr_handlers[];
> +extern const struct xattr_handler *fuse_no_acl_xattr_handlers[];
>  
>  struct posix_acl;
>  struct posix_acl *fuse_get_acl(struct inode *inode, int type);
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 1643043d4fe5..22c76cf8c2e3 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1100,6 +1100,13 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
>  	    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.
> +	 */
> +	if (sb->s_user_ns != &init_user_ns)
> +		sb->s_xattr = fuse_no_acl_xattr_handlers;
> +
>  	fc = kmalloc(sizeof(*fc), GFP_KERNEL);
>  	err = -ENOMEM;
>  	if (!fc)
> diff --git a/fs/fuse/xattr.c b/fs/fuse/xattr.c
> index 3caac46b08b0..433717640f78 100644
> --- a/fs/fuse/xattr.c
> +++ b/fs/fuse/xattr.c
> @@ -192,6 +192,26 @@ static int fuse_xattr_set(const struct xattr_handler *handler,
>  	return fuse_setxattr(inode, name, value, size, flags);
>  }
>  
> +static bool no_xattr_list(struct dentry *dentry)
> +{
> +	return false;
> +}
> +
> +static int no_xattr_get(const struct xattr_handler *handler,
> +			struct dentry *dentry, struct inode *inode,
> +			const char *name, void *value, size_t size)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int no_xattr_set(const struct xattr_handler *handler,
> +			struct dentry *dentry, struct inode *nodee,
> +			const char *name, const void *value,
> +			size_t size, int flags)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  static const struct xattr_handler fuse_xattr_handler = {
>  	.prefix = "",
>  	.get    = fuse_xattr_get,
> @@ -209,3 +229,26 @@ const struct xattr_handler *fuse_acl_xattr_handlers[] = {
>  	&fuse_xattr_handler,
>  	NULL
>  };
> +
> +static const struct xattr_handler fuse_no_acl_access_xattr_handler = {
> +	.name  = XATTR_NAME_POSIX_ACL_ACCESS,
> +	.flags = ACL_TYPE_ACCESS,
> +	.list  = no_xattr_list,
> +	.get   = no_xattr_get,
> +	.set   = no_xattr_set,
> +};
> +
> +static const struct xattr_handler fuse_no_acl_default_xattr_handler = {
> +	.name  = XATTR_NAME_POSIX_ACL_DEFAULT,
> +	.flags = ACL_TYPE_ACCESS,
> +	.list  = no_xattr_list,
> +	.get   = no_xattr_get,
> +	.set   = no_xattr_set,
> +};
> +
> +const struct xattr_handler *fuse_no_acl_xattr_handlers[] = {
> +	&fuse_no_acl_access_xattr_handler,
> +	&fuse_no_acl_default_xattr_handler,
> +	&fuse_xattr_handler,
> +	NULL
> +};