linux-kernel - Re: [PATCH RFC 5/6] exportfs: add permission method

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Message-ID: <20241202160452.2pg3qe4jymugp3su@quack3>
Date: Mon, 2 Dec 2024 17:04:52 +0100
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: Erin Shepherd <erin.shepherd@....eu>,
	Amir Goldstein <amir73il@...il.com>,
	Jeff Layton <jlayton@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
	Chuck Lever <chuck.lever@...cle.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: Re: [PATCH RFC 5/6] exportfs: add permission method

On Fri 29-11-24 14:38:04, Christian Brauner wrote:
> This allows filesystems such as pidfs to provide their custom permission
> checks.
> 
> Signed-off-by: Christian Brauner <brauner@...nel.org>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/fhandle.c             | 21 +++++++--------------
>  include/linux/exportfs.h | 17 ++++++++++++++++-
>  2 files changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/fhandle.c b/fs/fhandle.c
> index 031ad5592a0beabcc299436f037ad5fe626332e6..23491094032ec037066a271873ea8ff794616bee 100644
> --- a/fs/fhandle.c
> +++ b/fs/fhandle.c
> @@ -187,17 +187,6 @@ static int get_path_from_fd(int fd, struct path *root)
>  	return 0;
>  }
>  
> -enum handle_to_path_flags {
> -	HANDLE_CHECK_PERMS   = (1 << 0),
> -	HANDLE_CHECK_SUBTREE = (1 << 1),
> -};
> -
> -struct handle_to_path_ctx {
> -	struct path root;
> -	enum handle_to_path_flags flags;
> -	unsigned int fh_flags;
> -};
> -
>  static int vfs_dentry_acceptable(void *context, struct dentry *dentry)
>  {
>  	struct handle_to_path_ctx *ctx = context;
> @@ -335,15 +324,19 @@ static int handle_to_path(int mountdirfd, struct file_handle __user *ufh,
>  	struct file_handle f_handle;
>  	struct file_handle *handle = NULL;
>  	struct handle_to_path_ctx ctx = {};
> +	const struct export_operations *eops;
>  
>  	retval = get_path_from_fd(mountdirfd, &ctx.root);
>  	if (retval)
>  		goto out_err;
>  
> -	if (!may_decode_fh(&ctx, o_flags)) {
> -		retval = -EPERM;
> +	eops = ctx.root.mnt->mnt_sb->s_export_op;
> +	if (eops && eops->permission)
> +		retval = eops->permission(&ctx, o_flags);
> +	else
> +		retval = may_decode_fh(&ctx, o_flags);
> +	if (retval)
>  		goto out_path;
> -	}
>  
>  	if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) {
>  		retval = -EFAULT;
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index c69b79b64466d5bc32ffe9b2796a388130fe72d8..a087606ace194ccc9d1250f990ce55627aaf8dc5 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -3,6 +3,7 @@
>  #define LINUX_EXPORTFS_H 1
>  
>  #include <linux/types.h>
> +#include <linux/path.h>
>  
>  struct dentry;
>  struct iattr;
> @@ -10,7 +11,6 @@ struct inode;
>  struct iomap;
>  struct super_block;
>  struct vfsmount;
> -struct path;
>  
>  /* limit the handle size to NFSv4 handle size now */
>  #define MAX_HANDLE_SZ 128
> @@ -157,6 +157,17 @@ struct fid {
>  	};
>  };
>  
> +enum handle_to_path_flags {
> +	HANDLE_CHECK_PERMS   = (1 << 0),
> +	HANDLE_CHECK_SUBTREE = (1 << 1),
> +};
> +
> +struct handle_to_path_ctx {
> +	struct path root;
> +	enum handle_to_path_flags flags;
> +	unsigned int fh_flags;
> +};
> +
>  #define EXPORT_FH_CONNECTABLE	0x1 /* Encode file handle with parent */
>  #define EXPORT_FH_FID		0x2 /* File handle may be non-decodeable */
>  #define EXPORT_FH_DIR_ONLY	0x4 /* Only decode file handle for a directory */
> @@ -226,6 +237,9 @@ struct fid {
>   *    is also a directory.  In the event that it cannot be found, or storage
>   *    space cannot be allocated, a %ERR_PTR should be returned.
>   *
> + * permission:
> + *    Allow filesystems to specify a custom permission function.
> + *
>   * open:
>   *    Allow filesystems to specify a custom open function.
>   *
> @@ -255,6 +269,7 @@ struct export_operations {
>  			  bool write, u32 *device_generation);
>  	int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
>  			     int nr_iomaps, struct iattr *iattr);
> +	int (*permission)(struct handle_to_path_ctx *ctx, unsigned int oflags);
>  	struct file * (*open)(struct path *path, unsigned int oflags);
>  #define	EXPORT_OP_NOWCC			(0x1) /* don't collect v3 wcc data */
>  #define	EXPORT_OP_NOSUBTREECHK		(0x2) /* no subtree checking */
> 
> -- 
> 2.45.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR