[RFC PATCH v2 2/3] cifs: deprecate 'enable_negotiate_signing' module param

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We can blindly send a negotiate signing context on every negotiate call,
as it doesn't affect the current behaviour; even though we set AES-GMAC
as the first signing algorithm (i.e. our preferred algorithm), it will
use AES-CMAC if:

a) the server doesn't respond to signing negotiations
b) the server responds that it only supports AES-GMAC

So this is a safe change.

Throw a warning if 'enable_negotiate_signing=0' was explicitly set, but
ignore it and set it back to true.

Signed-off-by: Enzo Matsumiya <ematsumiya@xxxxxxx>
---
 fs/cifs/cifsfs.c   |  8 ++++++--
 fs/cifs/cifsglob.h |  3 ++-
 fs/cifs/smb2pdu.c  | 21 ++++++++++++---------
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index e9fb338b8e7e..40dcb0b73bea 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -65,7 +65,7 @@ bool lookupCacheEnabled = true;
 bool disable_legacy_dialects; /* false by default */
 bool enable_gcm_256 = true;
 bool require_gcm_256; /* false by default */
-bool enable_negotiate_signing; /* false by default */
+bool enable_negotiate_signing = true; /* deprecated -- always true now */
 unsigned int global_secflags = CIFSSEC_DEF;
 /* unsigned int ntlmv2_support = 0; */
 unsigned int sign_CIFS_PDUs = 1;
@@ -133,8 +133,12 @@ MODULE_PARM_DESC(enable_gcm_256, "Enable requesting strongest (256 bit) GCM encr
 module_param(require_gcm_256, bool, 0644);
 MODULE_PARM_DESC(require_gcm_256, "Require strongest (256 bit) GCM encryption. Default: n/N/0");
 
+/* XXX: remove this at some point */
 module_param(enable_negotiate_signing, bool, 0644);
-MODULE_PARM_DESC(enable_negotiate_signing, "Enable negotiating packet signing algorithm with server. Default: n/N/0");
+MODULE_PARM_DESC(enable_negotiate_signing,
+		 "(deprecated) Enable negotiating packet signing algorithm with the server. "
+		 "Default: always y/Y/1. Changing this setting no longer has any effect, cifs.ko "
+		 "will always try to negotiate the signing algorithm on SMB 3.1.1 mounts.");
 
 module_param(disable_legacy_dialects, bool, 0644);
 MODULE_PARM_DESC(disable_legacy_dialects, "To improve security it may be "
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index 0ce2ceaf039e..c1524e0ddad6 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -2015,7 +2015,8 @@ extern unsigned int global_secflags;	/* if on, session setup sent
 extern unsigned int sign_CIFS_PDUs;  /* enable smb packet signing */
 extern bool enable_gcm_256; /* allow optional negotiate of strongest signing (aes-gcm-256) */
 extern bool require_gcm_256; /* require use of strongest signing (aes-gcm-256) */
-extern bool enable_negotiate_signing; /* request use of faster (GMAC) signing if available */
+/* XXX: remove enable_negotiate_signing at some point */
+extern bool enable_negotiate_signing; /* (deprecated) request to use AES-GMAC signing if supported */
 extern bool linuxExtEnabled;/*enable Linux/Unix CIFS extensions*/
 extern unsigned int CIFSMaxBufSize;  /* max size not including hdr */
 extern unsigned int cifs_min_rcv;    /* min size of big ntwrk buf pool */
diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index 45215e4e6f37..d51dfe3bb163 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -614,14 +614,18 @@ assemble_neg_contexts(struct smb2_negotiate_req *req,
 		neg_context_count++;
 	}
 
-	if (enable_negotiate_signing) {
-		ctxt_len = build_signing_ctxt((struct smb2_signing_capabilities *)
-				pneg_ctxt);
-		*total_len += ctxt_len;
-		pneg_ctxt += ctxt_len;
-		neg_context_count++;
+	if (!enable_negotiate_signing) {
+		pr_warn("cifs.ko loaded with param 'enable_negotiate_signing=0', but this parameter "
+			"is deprecated. Trying to negotiate signing capabilities anyway...");
+		enable_negotiate_signing = true;
 	}
 
+	ctxt_len = build_signing_ctxt((struct smb2_signing_capabilities *)
+			pneg_ctxt);
+	*total_len += ctxt_len;
+	pneg_ctxt += ctxt_len;
+	neg_context_count++;
+
 	/* check for and add transport_capabilities and signing capabilities */
 	req->NegotiateContextCount = cpu_to_le16(neg_context_count);
 }
@@ -818,8 +822,7 @@ static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
 	}
 
 	/*
-	 * Throw a warning if user requested signing to be negotiated, but it
-	 * wasn't.
+	 * Throw a warning if signing context was not negotiated.
 	 *
 	 * Some servers will not send a SMB2_SIGNING_CAPABILITIES context (*),
 	 * so we use AES-CMAC (default in smb311 ops) as it is expected to be
@@ -827,7 +830,7 @@ static int smb311_decode_neg_context(struct smb2_negotiate_rsp *rsp,
 	 *
 	 * (*) see note "<125> Section 3.2.4.2.2.2" in MS-SMB2
 	 */
-	if (!server->signing_negotiated && enable_negotiate_signing)
+	if (!server->signing_negotiated)
 		cifs_dbg(VFS, "signing capabilities were not negotiated, using "
 			 "AES-CMAC for message signing\n");
 
-- 
2.35.3




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