linux-kernel - Re: [PATCH 2/2] cifs: Create native Window socket file compatible also with WSL subsystem

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Message-ID: <20250831094410.igrsfze7ci5mxkla@pali>
Date: Sun, 31 Aug 2025 11:44:10 +0200
From: Pali Rohár <pali@...nel.org>
To: Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@...guebit.com>
Cc: linux-cifs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] cifs: Create native Window socket file compatible
 also with WSL subsystem

Hello, I would like to remind this change.

On Saturday 12 July 2025 18:10:12 Pali Rohár wrote:
> After creating a native socket via the IO_REPARSE_TAG_AF_UNIX reparse
> point, try to set also the WSL EA $LXMOD.
> 
> This makes the native Win32 / NT socket file recognized also under
> WSL subsystem. WSL subsystem uses same reparse point tag but requires also
> to be EA $LXMOD set.
> 
> Fixes: 45a99d5d1173 ("cifs: Add support for creating native Windows sockets")
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
>  fs/smb/client/reparse.c | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
> index ee4af153e7af..74a36957e8cb 100644
> --- a/fs/smb/client/reparse.c
> +++ b/fs/smb/client/reparse.c
> @@ -381,7 +381,7 @@ static int detect_directory_symlink_target(struct cifs_sb_info *cifs_sb,
>  
>  static int create_native_socket(const unsigned int xid, struct inode *inode,
>  				struct dentry *dentry, struct cifs_tcon *tcon,
> -				const char *full_path)
> +				const char *full_path, umode_t mode)
>  {
>  	struct reparse_data_buffer buf = {
>  		.ReparseTag = cpu_to_le32(IO_REPARSE_TAG_AF_UNIX),
> @@ -395,6 +395,8 @@ static int create_native_socket(const unsigned int xid, struct inode *inode,
>  		.iov_base = &buf,
>  		.iov_len = sizeof(buf),
>  	};
> +	const __le64 xattr_mode_val = cpu_to_le64(mode);
> +	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
>  	struct inode *new;
>  	int rc = 0;
>  
> @@ -405,6 +407,28 @@ static int create_native_socket(const unsigned int xid, struct inode *inode,
>  		d_instantiate(dentry, new);
>  	else
>  		rc = PTR_ERR(new);
> +
> +	/*
> +	 * Try to set also optional WSL EA $LXMOD but ignore errors.
> +	 * WSL socket and native Win32/NT sockets uses same reparse point
> +	 * tag IO_REPARSE_TAG_AF_UNIX. WSL subsystem additionally requires
> +	 * EA $LXMOD to be set with the S_IFSOCK value. So setting this EA
> +	 * allows native socket to be recognized also by WSL subsystem.
> +	 * Note that setting of both EAs and reparse points is not supported
> +	 * by NTFS filesystem on Windows 8 / Windows Server 2012 and always
> +	 * fails. So ignore failures from this set_EA call.
> +	 */
> +#ifdef CONFIG_CIFS_XATTR
> +	if (!rc && tcon->ses->server->ops->set_EA &&
> +	    (le32_to_cpu(tcon->fsAttrInfo.Attributes) & FILE_SUPPORTS_EXTENDED_ATTRIBUTES))
> +		tcon->ses->server->ops->set_EA(xid, tcon, full_path,
> +					       true /* open reparse point */,
> +					       SMB2_WSL_XATTR_MODE,
> +					       &xattr_mode_val,
> +					       SMB2_WSL_XATTR_MODE_SIZE,
> +					       cifs_sb->local_nls, cifs_sb);
> +#endif
> +
>  	cifs_free_open_info(&data);
>  	return rc;
>  }
> @@ -714,7 +738,7 @@ int mknod_reparse(unsigned int xid, struct inode *inode,
>  	struct smb3_fs_context *ctx = CIFS_SB(inode->i_sb)->ctx;
>  
>  	if (S_ISSOCK(mode) && !ctx->nonativesocket && ctx->reparse_type != CIFS_REPARSE_TYPE_NONE)
> -		return create_native_socket(xid, inode, dentry, tcon, full_path);
> +		return create_native_socket(xid, inode, dentry, tcon, full_path, mode);
>  
>  	switch (ctx->reparse_type) {
>  	case CIFS_REPARSE_TYPE_NFS:
> -- 
> 2.20.1
>