There are cases where the server can return a cipher type of 0 and
it not be an error. For example, if server only supported AES256_CCM
(very unlikely) or server supported no encryption types or
had all disabled. In those cases encryption would not be supported,
but that can be ok if the client did not require encryption on mount.
In the case in which mount requested encryption ("seal" on mount)
then checks later on during tree connection will return the proper
rc, but if seal was not requested by client, since server is allowed
to return 0 to indicate no supported cipher, we should not fail mount.
Reported-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
--
Thanks,
Steve
From c6db40cc1a46730a78dc3e79d0791e10752d6853 Mon Sep 17 00:00:00 2001
From: Steve French <stfrench@xxxxxxxxxxxxx>
Date: Sat, 17 Oct 2020 03:54:27 -0500
Subject: [PATCH] smb3.1.1: do not fail if no encryption required but server
doesn't support it
There are cases where the server can return a cipher type of 0 and
it not be an error. For example, if server only supported AES256_CCM
(very unlikely) or server supported no encryption types or
had all disabled. In those cases encryption would not be supported,
but that can be ok if the client did not require encryption on mount.
In the case in which mount requested encryption ("seal" on mount)
then checks later on during tree connection will return the proper
rc, but if seal was not requested by client, since server is allowed
to return 0 to indicate no supported cipher, we should not fail mount.
Reported-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
---
fs/cifs/smb2pdu.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index d504bc296349..025db5e8c183 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -616,9 +616,19 @@ static int decode_encrypt_ctx(struct TCP_Server_Info *server,
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;
+ /*
+ * e.g. if server only supported AES256_CCM (very unlikely)
+ * or server supported no encryption types or had all disabled.
+ * Since GLOBAL_CAP_ENCRYPTION will be not set, in the case
+ * in which mount requested encryption ("seal") checks later
+ * on during tree connection will return proper rc, but if
+ * seal not requested by client, since server is allowed to
+ * return 0 to indicate no supported cipher, we can't fail here
+ */
+ server->cipher_type = 0;
+ server->capabilities &= ~SMB2_GLOBAL_CAP_ENCRYPTION;
+ pr_warn_once("Server does not support requested encryption types\n");
+ return 0;
} else if ((ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_CCM) &&
(ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES128_GCM) &&
(ctxt->Ciphers[0] != SMB2_ENCRYPTION_AES256_GCM)) {
--
2.25.1
