[PATCH 3/4] cifs: Validate EAs for WSL reparse points

["Pali Rohár" <pali@kernel.org>]

Major and minor numbers for char and block devices are mandatory for stat.
So check that the WSL EA $LXDEV is present for WSL CHR and BLK reparse
points.

WSL reparse point tag determinate type of the file. But file type is
present also in the WSL EA $LXMOD. So check that both file types are same.

Fixes: 78e26bec4d6d ("smb: client: parse uid, gid, mode and dev from WSL reparse points")
Signed-off-by: Pali Rohár <pali@kernel.org>
---
 fs/smb/client/reparse.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/fs/smb/client/reparse.c b/fs/smb/client/reparse.c
index 9fe9dd71a6fa..9e40f5709c7f 100644
--- a/fs/smb/client/reparse.c
+++ b/fs/smb/client/reparse.c
@@ -1105,11 +1105,12 @@ struct reparse_data_buffer *smb2_get_reparse_point_buffer(const struct kvec *rsp
 					      le32_to_cpu(io->OutputOffset));
 }
 
-static void wsl_to_fattr(struct cifs_open_info_data *data,
+static bool wsl_to_fattr(struct cifs_open_info_data *data,
 			 struct cifs_sb_info *cifs_sb,
 			 u32 tag, struct cifs_fattr *fattr)
 {
 	struct smb2_file_full_ea_info *ea;
+	bool have_xattr_dev = false;
 	u32 next = 0;
 
 	switch (tag) {
@@ -1152,13 +1153,24 @@ static void wsl_to_fattr(struct cifs_open_info_data *data,
 			fattr->cf_uid = wsl_make_kuid(cifs_sb, v);
 		else if (!strncmp(name, SMB2_WSL_XATTR_GID, nlen))
 			fattr->cf_gid = wsl_make_kgid(cifs_sb, v);
-		else if (!strncmp(name, SMB2_WSL_XATTR_MODE, nlen))
+		else if (!strncmp(name, SMB2_WSL_XATTR_MODE, nlen)) {
+			/* File type in reparse point tag and in xattr mode must match. */
+			if (S_DT(fattr->cf_mode) != S_DT(le32_to_cpu(*(__le32 *)v)))
+				return false;
 			fattr->cf_mode = (umode_t)le32_to_cpu(*(__le32 *)v);
-		else if (!strncmp(name, SMB2_WSL_XATTR_DEV, nlen))
+		} else if (!strncmp(name, SMB2_WSL_XATTR_DEV, nlen)) {
 			fattr->cf_rdev = reparse_mkdev(v);
+			have_xattr_dev = true;
+		}
 	} while (next);
 out:
+
+	/* Major and minor numbers for char and block devices are mandatory. */
+	if (!have_xattr_dev && (tag == IO_REPARSE_TAG_LX_CHR || tag == IO_REPARSE_TAG_LX_BLK))
+		return false;
+
 	fattr->cf_dtype = S_DT(fattr->cf_mode);
+	return true;
 }
 
 static bool posix_reparse_to_fattr(struct cifs_sb_info *cifs_sb,
@@ -1221,7 +1233,9 @@ bool cifs_reparse_point_to_fattr(struct cifs_sb_info *cifs_sb,
 	case IO_REPARSE_TAG_AF_UNIX:
 	case IO_REPARSE_TAG_LX_CHR:
 	case IO_REPARSE_TAG_LX_BLK:
-		wsl_to_fattr(data, cifs_sb, tag, fattr);
+		ok = wsl_to_fattr(data, cifs_sb, tag, fattr);
+		if (!ok)
+			return false;
 		break;
 	case IO_REPARSE_TAG_NFS:
 		ok = posix_reparse_to_fattr(cifs_sb, fattr, data);
-- 
2.20.1