[PATCH 4.18 123/197] smb3: if server does not support posix do not allow posix mount option

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Steve French <stfrench@xxxxxxxxxxxxx>

[ Upstream commit 8505c8bfd85a260c9dc5c47e15bd8c5357fcbcd2 ]

If user specifies "posix" on an SMB3.11 mount, then fail the mount
if server does not return the POSIX negotiate context indicating
support for posix.

Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Reviewed-by: Aurelien Aptel <aaptel@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/cifs/connect.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -3031,11 +3031,15 @@ cifs_get_tcon(struct cifs_ses *ses, stru
 	}
 
 #ifdef CONFIG_CIFS_SMB311
-	if ((volume_info->linux_ext) && (ses->server->posix_ext_supported)) {
-		if (ses->server->vals->protocol_id == SMB311_PROT_ID) {
+	if (volume_info->linux_ext) {
+		if (ses->server->posix_ext_supported) {
 			tcon->posix_extensions = true;
 			printk_once(KERN_WARNING
 				"SMB3.11 POSIX Extensions are experimental\n");
+		} else {
+			cifs_dbg(VFS, "Server does not support mounting with posix SMB3.11 extensions.\n");
+			rc = -EOPNOTSUPP;
+			goto out_fail;
 		}
 	}
 #endif /* 311 */