CIFS: add CONFIG_CIFS_DEBUG_KEYS to dump encryption keys

Add new config option that dumps AES keys to the console when they are
generated. This is obviously for debugging purposes only, and should not
be enabled otherwise.
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/Kconfig

@@ -146,6 +146,15 @@ config CIFS_DEBUG2
 	   option can be turned off unless you are debugging
 	   cifs problems.  If unsure, say N.
 
+config CIFS_DEBUG_DUMP_KEYS
+	bool "Dump encryption keys for offline decryption (Unsafe)"
+	depends on CIFS_DEBUG && CIFS_SMB2
+	help
+	   Enabling this will dump the encryption and decryption keys
+	   used to communicate on an encrypted share connection on the
+	   console. This allows Wireshark to decrypt and dissect
+	   encrypted network captures. Enable this carefully.
+
 config CIFS_DFS_UPCALL
 	  bool "DFS feature support"
 	  depends on CIFS && KEYS

fs/cifs/smb2transport.c

@@ -335,9 +335,31 @@ generate_smb3signingkey(struct cifs_ses *ses,
 	if (rc)
 		return rc;
 
-	return generate_key(ses, ptriplet->decryption.label,
+	rc = generate_key(ses, ptriplet->decryption.label,
 			  ptriplet->decryption.context,
 			  ses->smb3decryptionkey, SMB3_SIGN_KEY_SIZE);
+
+	if (rc)
+		return rc;
+
+#ifdef CONFIG_CIFS_DEBUG_DUMP_KEYS
+	cifs_dbg(VFS, "%s: dumping generated AES session keys\n", __func__);
+	/*
+	 * The session id is opaque in terms of endianness, so we can't
+	 * print it as a long long. we dump it as we got it on the wire
+	 */
+	cifs_dbg(VFS, "Session Id    %*ph\n", (int)sizeof(ses->Suid),
+			&ses->Suid);
+	cifs_dbg(VFS, "Session Key   %*ph\n",
+		 SMB2_NTLMV2_SESSKEY_SIZE, ses->auth_key.response);
+	cifs_dbg(VFS, "Signing Key   %*ph\n",
+		 SMB3_SIGN_KEY_SIZE, ses->smb3signingkey);
+	cifs_dbg(VFS, "ServerIn Key  %*ph\n",
+		 SMB3_SIGN_KEY_SIZE, ses->smb3encryptionkey);
+	cifs_dbg(VFS, "ServerOut Key %*ph\n",
+		 SMB3_SIGN_KEY_SIZE, ses->smb3decryptionkey);
+#endif
+	return rc;
 }
 
 int