From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 65E4E171CD for ; Mon, 18 May 2026 01:24:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779067446; cv=none; b=XCXzaWOx9+F2106SK42llYmHGuIDmPSh/mUeaLwNrGppXuAeMwmk+WnP0bf5Tt56mCTfHpsKVEbWS+KIvt9jnfEz3vzRDW+0jpEqjruvyAPJPXH3a/9prIGIQeIVCS0CBbhScDr7YZhEo7RYuH5wAmoiym4E6K9GK7TgHOpiKvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779067446; c=relaxed/simple; bh=LpbIZaR0pcMaO9d5MlC67SseMt39cBH5xgQk9+mdUWA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jL2YTzz/jRy3JS2By08I/d5kxcg66vQMah73TtZPmkSs/izMIKSWlsL6VxPrmkIneDjfxlPAoCM+xs/jJLX0UcTKvVj1P+Za/5LqnLOBY0LN4huBMK4IYAVVUcxMDxb9W9N8hdmeo30W43AuYfP/mtVpiX5HeOF98L77m25klYE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GZlCI2xf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GZlCI2xf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A2A4C2BCB0; Mon, 18 May 2026 01:24:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1779067446; bh=LpbIZaR0pcMaO9d5MlC67SseMt39cBH5xgQk9+mdUWA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GZlCI2xf5l0mn6u4r6SEdOI7F2t0fREEnYGZymI9pLPkxJa8AvCyj0XEe1hj3r7Rk oq13coqbrxXQnRruZkS1ZS06FwexWunMKirx554/XnkRmD8K5s23xD/r8o27YH7Wxt c4jP2/eAGWg2dutYMy5lZCh5UVrylMX02FGwxeSfJX0/0Cp5dXK9eJ/o+s4++eruxd etHR0fvtWPcR3iolPo1IE++TnYj7SSkiHuT6pwRDfCl6nvgn3iAA5UY2SOc5gFrG0c pfyrdjehRlOzW9MCRPtWk5L/LeRhLL9PfRq5Qm4OParmN8jkz8E6WklLl1aTwxvAMz tw5gZtZBMUNFQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Piyush Sachdeva , Bharath SM , Piyush Sachdeva , Steve French , Sasha Levin Subject: [PATCH 5.10.y] smb: client: Use FullSessionKey for AES-256 encryption key derivation Date: Sun, 17 May 2026 21:24:03 -0400 Message-ID: <20260518012403.482990-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026051204-landside-tartly-eedd@gregkh> References: <2026051204-landside-tartly-eedd@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Piyush Sachdeva [ Upstream commit 5be7a0cef3229fb3b63a07c0d289daf752545424 ] When Kerberos authentication is used with AES-256 encryption (AES-256-CCM or AES-256-GCM), the SMB3 encryption and decryption keys must be derived using the full session key (Session.FullSessionKey) rather than just the first 16 bytes (Session.SessionKey). Per MS-SMB2 section 3.2.5.3.1, when Connection.Dialect is "3.1.1" and Connection.CipherId is AES-256-CCM or AES-256-GCM, Session.FullSessionKey must be set to the full cryptographic key from the GSS authentication context. The encryption and decryption key derivation (SMBC2SCipherKey, SMBS2CCipherKey) must use this FullSessionKey as the KDF input. The signing key derivation continues to use Session.SessionKey (first 16 bytes) in all cases. Previously, generate_key() hardcoded SMB2_NTLMV2_SESSKEY_SIZE (16) as the HMAC-SHA256 key input length for all derivations. When Kerberos with AES-256 provides a 32-byte session key, the KDF for encryption/decryption was using only the first 16 bytes, producing keys that did not match the server's, causing mount failures with sec=krb5 and require_gcm_256=1. Add a full_key_size parameter to generate_key() and pass the appropriate size from generate_smb3signingkey(): - Signing: always SMB2_NTLMV2_SESSKEY_SIZE (16 bytes) - Encryption/Decryption: ses->auth_key.len when AES-256, otherwise 16 Also fix cifs_dump_full_key() to report the actual session key length for AES-256 instead of hardcoded CIFS_SESS_KEY_SIZE, so that userspace tools like Wireshark receive the correct key for decryption. Cc: Reviewed-by: Bharath SM Signed-off-by: Piyush Sachdeva Signed-off-by: Piyush Sachdeva Signed-off-by: Steve French [ adapted to old crypto_shash API ] Signed-off-by: Sasha Levin --- fs/cifs/smb2transport.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/fs/cifs/smb2transport.c b/fs/cifs/smb2transport.c index c02e57d8e228b..e4cea6c2d835e 100644 --- a/fs/cifs/smb2transport.c +++ b/fs/cifs/smb2transport.c @@ -305,7 +305,8 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server, } static int generate_key(struct cifs_ses *ses, struct kvec label, - struct kvec context, __u8 *key, unsigned int key_size) + struct kvec context, __u8 *key, unsigned int key_size, + unsigned int full_key_size) { unsigned char zero = 0x0; __u8 i[4] = {0, 0, 0, 1}; @@ -326,7 +327,7 @@ static int generate_key(struct cifs_ses *ses, struct kvec label, } rc = crypto_shash_setkey(server->secmech.hmacsha256, - ses->auth_key.response, SMB2_NTLMV2_SESSKEY_SIZE); + ses->auth_key.response, full_key_size); if (rc) { cifs_server_dbg(VFS, "%s: Could not set with session key\n", __func__); goto smb3signkey_ret; @@ -407,10 +408,9 @@ static int generate_smb3signingkey(struct cifs_ses *ses, const struct derivation_triplet *ptriplet) { - int rc; -#ifdef CONFIG_CIFS_DEBUG_DUMP_KEYS + unsigned int full_key_size = SMB2_NTLMV2_SESSKEY_SIZE; struct TCP_Server_Info *server = ses->server; -#endif + int rc; /* * All channels use the same encryption/decryption keys but @@ -426,30 +426,46 @@ generate_smb3signingkey(struct cifs_ses *ses, rc = generate_key(ses, ptriplet->signing.label, ptriplet->signing.context, cifs_ses_binding_channel(ses)->signkey, - SMB3_SIGN_KEY_SIZE); + SMB3_SIGN_KEY_SIZE, + SMB2_NTLMV2_SESSKEY_SIZE); if (rc) return rc; } else { rc = generate_key(ses, ptriplet->signing.label, ptriplet->signing.context, ses->smb3signingkey, - SMB3_SIGN_KEY_SIZE); + SMB3_SIGN_KEY_SIZE, + SMB2_NTLMV2_SESSKEY_SIZE); if (rc) return rc; + /* + * Per MS-SMB2 3.2.5.3.1, signing key always uses Session.SessionKey + * (first 16 bytes). Encryption/decryption keys use + * Session.FullSessionKey when dialect is 3.1.1 and cipher is + * AES-256-CCM or AES-256-GCM, otherwise Session.SessionKey. + */ + + if (server->dialect == SMB311_PROT_ID && + (server->cipher_type == SMB2_ENCRYPTION_AES256_CCM || + server->cipher_type == SMB2_ENCRYPTION_AES256_GCM)) + full_key_size = ses->auth_key.len; + memcpy(ses->chans[0].signkey, ses->smb3signingkey, SMB3_SIGN_KEY_SIZE); rc = generate_key(ses, ptriplet->encryption.label, ptriplet->encryption.context, ses->smb3encryptionkey, - SMB3_ENC_DEC_KEY_SIZE); + SMB3_ENC_DEC_KEY_SIZE, + full_key_size); if (rc) return rc; rc = generate_key(ses, ptriplet->decryption.label, ptriplet->decryption.context, ses->smb3decryptionkey, - SMB3_ENC_DEC_KEY_SIZE); + SMB3_ENC_DEC_KEY_SIZE, + full_key_size); if (rc) return rc; } @@ -464,7 +480,7 @@ generate_smb3signingkey(struct cifs_ses *ses, &ses->Suid); cifs_dbg(VFS, "Cipher type %d\n", server->cipher_type); cifs_dbg(VFS, "Session Key %*ph\n", - SMB2_NTLMV2_SESSKEY_SIZE, ses->auth_key.response); + (int)ses->auth_key.len, ses->auth_key.response); cifs_dbg(VFS, "Signing Key %*ph\n", SMB3_SIGN_KEY_SIZE, ses->smb3signingkey); if ((server->cipher_type == SMB2_ENCRYPTION_AES256_CCM) || -- 2.53.0