Re: [PATCH v7 08/15] fs: add __remove_file_privs() with flags parameter

[Jan Kara <jack@suse.cz>]

On Wed 01-06-22 14:01:34, Stefan Roesch wrote:
> This adds the function __remove_file_privs, which allows the caller to
> pass the kiocb flags parameter.
> 
> No intended functional changes in this patch.
> 
> Signed-off-by: Stefan Roesch <shr@fb.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/inode.c | 57 +++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 37 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 9d9b422504d1..ac1cf5aa78c8 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -2010,36 +2010,43 @@ static int __remove_privs(struct user_namespace *mnt_userns,
>  	return notify_change(mnt_userns, dentry, &newattrs, NULL);
>  }
>  
> -/*
> - * Remove special file priviledges (suid, capabilities) when file is written
> - * to or truncated.
> - */
> -int file_remove_privs(struct file *file)
> +static int __file_remove_privs(struct file *file, unsigned int flags)
>  {
>  	struct dentry *dentry = file_dentry(file);
>  	struct inode *inode = file_inode(file);
> +	int error;
>  	int kill;
> -	int error = 0;
>  
> -	/*
> -	 * Fast path for nothing security related.
> -	 * As well for non-regular files, e.g. blkdev inodes.
> -	 * For example, blkdev_write_iter() might get here
> -	 * trying to remove privs which it is not allowed to.
> -	 */
>  	if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
>  		return 0;
>  
>  	kill = dentry_needs_remove_privs(dentry);
> -	if (kill < 0)
> +	if (kill <= 0)
>  		return kill;
> -	if (kill)
> -		error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
> +
> +	if (flags & IOCB_NOWAIT)
> +		return -EAGAIN;
> +
> +	error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
>  	if (!error)
>  		inode_has_no_xattr(inode);
>  
>  	return error;
>  }
> +
> +/**
> + * file_remove_privs - remove special file privileges (suid, capabilities)
> + * @file: file to remove privileges from
> + *
> + * When file is modified by a write or truncation ensure that special
> + * file privileges are removed.
> + *
> + * Return: 0 on success, negative errno on failure.
> + */
> +int file_remove_privs(struct file *file)
> +{
> +	return __file_remove_privs(file, 0);
> +}
>  EXPORT_SYMBOL(file_remove_privs);
>  
>  /**
> @@ -2090,18 +2097,28 @@ int file_update_time(struct file *file)
>  }
>  EXPORT_SYMBOL(file_update_time);
>  
> -/* Caller must hold the file's inode lock */
> +/**
> + * file_modified - handle mandated vfs changes when modifying a file
> + * @file: file that was modified
> + *
> + * When file has been modified ensure that special
> + * file privileges are removed and time settings are updated.
> + *
> + * Context: Caller must hold the file's inode lock.
> + *
> + * Return: 0 on success, negative errno on failure.
> + */
>  int file_modified(struct file *file)
>  {
> -	int err;
> +	int ret;
>  
>  	/*
>  	 * Clear the security bits if the process is not being run by root.
>  	 * This keeps people from modifying setuid and setgid binaries.
>  	 */
> -	err = file_remove_privs(file);
> -	if (err)
> -		return err;
> +	ret = __file_remove_privs(file, 0);
> +	if (ret)
> +		return ret;
>  
>  	if (unlikely(file->f_mode & FMODE_NOCMTIME))
>  		return 0;
> -- 
> 2.30.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR