[PATCH 3/5] cifs: Fix validation of SMB2_OP_QUERY_WSL_EA response size

[Pali Rohár]

Currently the SMB2_OP_QUERY_WSL_EA checks that response buffer has at least
size SMB2_WSL_MIN_QUERY_EA_RESP_SIZE and maximally it is
SMB2_WSL_MAX_QUERY_EA_RESP_SIZE.

Constant SMB2_WSL_MIN_QUERY_EA_RESP_SIZE is defined wrongly because it
expects that the there are at least 3 EAs. But WSL subsystem has only one
mandatory EA: $LXMOD. So fix the SMB2_WSL_MIN_QUERY_EA_RESP_SIZE to be size
of the structure of one EA.

Relax also SMB2_WSL_MAX_QUERY_EA_RESP_SIZE, calculate maximum size from the
size of the largest EA which is 8 bytes for $LXDEV.

This change allows to recognize WSL CHR and BLK reparse points which have
only $LXMOD and $LXDEV EAs (no $LXUID or $LXGID). WSL subsystem recognize
such reparse points too.

Fixes: ea41367b2a60 ("smb: client: introduce SMB2_OP_QUERY_WSL_EA")
Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
---
 fs/smb/client/smb2pdu.h | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/fs/smb/client/smb2pdu.h b/fs/smb/client/smb2pdu.h
index 3c09a58dfd07..cdf0ab9ddbcd 100644
--- a/fs/smb/client/smb2pdu.h
+++ b/fs/smb/client/smb2pdu.h
@@ -425,24 +425,23 @@ struct smb2_create_ea_ctx {
 #define SMB2_WSL_XATTR_MODE		"$LXMOD"
 #define SMB2_WSL_XATTR_DEV		"$LXDEV"
 #define SMB2_WSL_XATTR_NAME_LEN	6
-#define SMB2_WSL_NUM_XATTRS		4
 
 #define SMB2_WSL_XATTR_UID_SIZE	4
 #define SMB2_WSL_XATTR_GID_SIZE	4
 #define SMB2_WSL_XATTR_MODE_SIZE	4
 #define SMB2_WSL_XATTR_DEV_SIZE	8
 
+/* minimal size: at least the smallest EA has to be present */
 #define SMB2_WSL_MIN_QUERY_EA_RESP_SIZE \
-	(ALIGN((SMB2_WSL_NUM_XATTRS - 1) * \
-	       (SMB2_WSL_XATTR_NAME_LEN + 1 + \
-		sizeof(struct smb2_file_full_ea_info)), 4) + \
-	 SMB2_WSL_XATTR_NAME_LEN + 1 + sizeof(struct smb2_file_full_ea_info))
+	(sizeof(struct smb2_file_full_ea_info) + SMB2_WSL_XATTR_NAME_LEN + 1 + 4)
 
+/*
+ * maximal size: all 4 EAs are present,
+ * beginning of each EA structure has to be aligned to 4 bytes,
+ * EAs have different size and can be returned in any other,
+ * use the largest EA size for aligning when calculating maximal size
+ */
 #define SMB2_WSL_MAX_QUERY_EA_RESP_SIZE \
-	(ALIGN(SMB2_WSL_MIN_QUERY_EA_RESP_SIZE + \
-	       SMB2_WSL_XATTR_UID_SIZE + \
-	       SMB2_WSL_XATTR_GID_SIZE + \
-	       SMB2_WSL_XATTR_MODE_SIZE + \
-	       SMB2_WSL_XATTR_DEV_SIZE, 4))
+	4 * ALIGN((sizeof(struct smb2_file_full_ea_info) + SMB2_WSL_XATTR_NAME_LEN + 1 + 8), 4)
 
 #endif				/* _SMB2PDU_H */
-- 
2.20.1