Re: [PATCH v3 01/10] xattr: break delegations in {set,remove}xattr

[Frank van der Linden <fllinden@amazon.com>]

Hi Al,

Do you have any comments / concerns about this patch? It's part of nfs
server side user xattr support, full series here:

https://lore.kernel.org/linux-nfs/20200623223927.31795-1-fllinden@amazon.com/

I copied this one to linux-fsdevel and you, just giving you an extra
ping. Bruce/Chuck are OK with the rest of the series, so I just need
your ACK on this one, and the next one (will send the ping separately).

Thanks,

- Frank


On Tue, Jun 23, 2020 at 10:39:18PM +0000, Frank van der Linden wrote:
> set/removexattr on an exported filesystem should break NFS delegations.
> This is true in general, but also for the upcoming support for
> RFC 8726 (NFSv4 extended attribute support). Make sure that they do.
> 
> Additonally, they need to grow a _locked variant, since callers might
> call this with i_rwsem held (like the NFS server code).
> 
> Cc: stable@vger.kernel.org
> Cc: linux-fsdevel@vger.kernel.org
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> ---
>  fs/xattr.c            | 84 +++++++++++++++++++++++++++++++++++++++----
>  include/linux/xattr.h |  2 ++
>  2 files changed, 79 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index 91608d9bfc6a..95f38f57347f 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -204,10 +204,22 @@ int __vfs_setxattr_noperm(struct dentry *dentry, const char *name,
>  	return error;
>  }
>  
> -
> +/**
> + * __vfs_setxattr_locked: set an extended attribute while holding the inode
> + * lock
> + *
> + *  @dentry - object to perform setxattr on
> + *  @name - xattr name to set
> + *  @value - value to set @name to
> + *  @size - size of @value
> + *  @flags - flags to pass into filesystem operations
> + *  @delegated_inode - on return, will contain an inode pointer that
> + *  a delegation was broken on, NULL if none.
> + */
>  int
> -vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> -		size_t size, int flags)
> +__vfs_setxattr_locked(struct dentry *dentry, const char *name,
> +		const void *value, size_t size, int flags,
> +		struct inode **delegated_inode)
>  {
>  	struct inode *inode = dentry->d_inode;
>  	int error;
> @@ -216,15 +228,40 @@ vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
>  	if (error)
>  		return error;
>  
> -	inode_lock(inode);
>  	error = security_inode_setxattr(dentry, name, value, size, flags);
>  	if (error)
>  		goto out;
>  
> +	error = try_break_deleg(inode, delegated_inode);
> +	if (error)
> +		goto out;
> +
>  	error = __vfs_setxattr_noperm(dentry, name, value, size, flags);
>  
>  out:
> +	return error;
> +}
> +EXPORT_SYMBOL_GPL(__vfs_setxattr_locked);
> +
> +int
> +vfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> +		size_t size, int flags)
> +{
> +	struct inode *inode = dentry->d_inode;
> +	struct inode *delegated_inode = NULL;
> +	int error;
> +
> +retry_deleg:
> +	inode_lock(inode);
> +	error = __vfs_setxattr_locked(dentry, name, value, size, flags,
> +	    &delegated_inode);
>  	inode_unlock(inode);
> +
> +	if (delegated_inode) {
> +		error = break_deleg_wait(&delegated_inode);
> +		if (!error)
> +			goto retry_deleg;
> +	}
>  	return error;
>  }
>  EXPORT_SYMBOL_GPL(vfs_setxattr);
> @@ -378,8 +415,18 @@ __vfs_removexattr(struct dentry *dentry, const char *name)
>  }
>  EXPORT_SYMBOL(__vfs_removexattr);
>  
> +/**
> + * __vfs_removexattr_locked: set an extended attribute while holding the inode
> + * lock
> + *
> + *  @dentry - object to perform setxattr on
> + *  @name - name of xattr to remove
> + *  @delegated_inode - on return, will contain an inode pointer that
> + *  a delegation was broken on, NULL if none.
> + */
>  int
> -vfs_removexattr(struct dentry *dentry, const char *name)
> +__vfs_removexattr_locked(struct dentry *dentry, const char *name,
> +		struct inode **delegated_inode)
>  {
>  	struct inode *inode = dentry->d_inode;
>  	int error;
> @@ -388,11 +435,14 @@ vfs_removexattr(struct dentry *dentry, const char *name)
>  	if (error)
>  		return error;
>  
> -	inode_lock(inode);
>  	error = security_inode_removexattr(dentry, name);
>  	if (error)
>  		goto out;
>  
> +	error = try_break_deleg(inode, delegated_inode);
> +	if (error)
> +		goto out;
> +
>  	error = __vfs_removexattr(dentry, name);
>  
>  	if (!error) {
> @@ -401,12 +451,32 @@ vfs_removexattr(struct dentry *dentry, const char *name)
>  	}
>  
>  out:
> +	return error;
> +}
> +EXPORT_SYMBOL_GPL(__vfs_removexattr_locked);
> +
> +int
> +vfs_removexattr(struct dentry *dentry, const char *name)
> +{
> +	struct inode *inode = dentry->d_inode;
> +	struct inode *delegated_inode = NULL;
> +	int error;
> +
> +retry_deleg:
> +	inode_lock(inode);
> +	error = __vfs_removexattr_locked(dentry, name, &delegated_inode);
>  	inode_unlock(inode);
> +
> +	if (delegated_inode) {
> +		error = break_deleg_wait(&delegated_inode);
> +		if (!error)
> +			goto retry_deleg;
> +	}
> +
>  	return error;
>  }
>  EXPORT_SYMBOL_GPL(vfs_removexattr);
>  
> -
>  /*
>   * Extended attribute SET operations
>   */
> diff --git a/include/linux/xattr.h b/include/linux/xattr.h
> index 47eaa34f8761..a2f3cd02653c 100644
> --- a/include/linux/xattr.h
> +++ b/include/linux/xattr.h
> @@ -51,8 +51,10 @@ ssize_t vfs_getxattr(struct dentry *, const char *, void *, size_t);
>  ssize_t vfs_listxattr(struct dentry *d, char *list, size_t size);
>  int __vfs_setxattr(struct dentry *, struct inode *, const char *, const void *, size_t, int);
>  int __vfs_setxattr_noperm(struct dentry *, const char *, const void *, size_t, int);
> +int __vfs_setxattr_locked(struct dentry *, const char *, const void *, size_t, int, struct inode **);
>  int vfs_setxattr(struct dentry *, const char *, const void *, size_t, int);
>  int __vfs_removexattr(struct dentry *, const char *);
> +int __vfs_removexattr_locked(struct dentry *, const char *, struct inode **);
>  int vfs_removexattr(struct dentry *, const char *);
>  
>  ssize_t generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size);
> -- 
> 2.17.2
>