[FOCAL][PATCH 4/7] smb3.1.1: print warning if server does not support requested encryption type

[Tim Gardner]

From: Steve French <stfrench at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/1921916

If server does not support AES-256-GCM and it was required on mount, print
warning message. Also log and return a different error message (EOPNOTSUPP)
when encryption mechanism is not supported vs the case when an unknown
unrequested encryption mechanism could be returned (EINVAL).

Signed-off-by: Steve French <stfrench at microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov at microsoft.com>
(backported from commit 511ac89e591ab9affce17a8be4c45f6c2bb837f0)
[rtg - minor context differences]
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 fs/cifs/smb2pdu.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 9f337d224d2b..13c7e799323c 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -676,8 +676,19 @@ static int decode_encrypt_ctx(struct TCP_Server_Info *server,
 		return -EINVAL;
 	}
 	cifs_dbg(FYI, "SMB311 cipher type:%d\n", le16_to_cpu(ctxt->Ciphers[0]));
-	if ((ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_CCM) &&
-	    (ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_GCM)) {
+	if (require_gcm_256) {
+		if (ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES256_GCM) {
+			cifs_dbg(VFS, "Server does not support requested encryption type (AES256 GCM)\n");
+			return -EOPNOTSUPP;
+		}
+	} else if (ctxt->Ciphers[0] == 0) {
+		/* e.g. if server only supported AES256_CCM (very unlikely) */
+		cifs_dbg(VFS, "Server does not support requested encryption types\n");
+		return -EOPNOTSUPP;
+	} else if ((ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_CCM) &&
+		   (ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_GCM) &&
+		   (ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES256_GCM)) {
+		/* server returned a cipher we didn't ask for */
 		printk_once(KERN_WARNING "invalid SMB3.11 cipher returned\n");
 		return -EINVAL;
 	}
-- 
2.17.1