linux-kernel - [PATCH 5/5] cifs: Validate presence of EA $LXMOD for WSL reparse points

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Message-Id: <20250608170119.6813-6-pali@kernel.org>
Date: Sun,  8 Jun 2025 19:01:19 +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: [PATCH 5/5] cifs: Validate presence of EA $LXMOD for WSL reparse points

S_DT part of EA $LXMOD is mandatory for all WSL reparse points except the
WSL symlink and Win32 socket. Microsoft WSL subsystem does not recognize
them without EA $LXMOD too, and treat such inodes as regular files.

Fixes: ef201e8759d2 ("cifs: Validate EAs for WSL reparse points")
Fixes: 78e26bec4d6d ("smb: client: parse uid, gid, mode and dev from WSL reparse points")
Signed-off-by: Pali Rohár <pali@...nel.org>
---
 fs/smb/client/reparse.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 8d989e436517..3dffd5f0dc07 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -1118,6 +1118,7 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 {
 	struct smb2_file_full_ea_info *ea;
 	bool ignore_missing_eas = false;
+	bool have_xattr_mode = false;
 	bool have_xattr_dev = false;
 	umode_t reparse_mode_type = 0;
 	u32 next = 0;
@@ -1177,6 +1178,7 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 			if (S_DT(reparse_mode_type) != S_DT(le32_to_cpu(*(__le32 *)v)))
 				return false;
 			fattr->cf_mode = (umode_t)le32_to_cpu(*(__le32 *)v);
+			have_xattr_mode = true;
 		} else if (!strncmp(name, SMB2_WSL_XATTR_DEV, nlen)) {
 			fattr->cf_rdev = reparse_mkdev(v);
 			have_xattr_dev = true;
@@ -1188,6 +1190,16 @@ static bool wsl_to_fattr(struct cifs_open_info_data *data,
 	if (!have_xattr_dev && (tag == IO_REPARSE_TAG_LX_CHR || tag == IO_REPARSE_TAG_LX_BLK))
 		return ignore_missing_eas;
 
+	/*
+	 * S_DT part of xattr MODE is mandatory for all WSL reparse points except the WSL symlink.
+	 * Microsoft WSL does not recognize them without xattr MODE too (except the WSL symlink).
+	 * IO_REPARSE_TAG_AF_UNIX is here an exception because this reparse point is used by both
+	 * WSL subsystem and native NT/WinAPI subsystems. And NT/WinAPI creates AF UNIX socket
+	 * without the xattr MODE and recognize it also without the xattr MODE.
+	 */
+	if (!have_xattr_mode && (tag != IO_REPARSE_TAG_AF_UNIX && tag != IO_REPARSE_TAG_LX_SYMLINK))
+		return ignore_missing_eas;
+
 	fattr->cf_mode |= reparse_mode_type;
 	return true;
 }
-- 
2.20.1