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FAILED: patch "[PATCH] smb: client: Use FullSessionKey for AES-256 encryption key" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 2 messages May 12 – May 17

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Stable branch SMB client (CIFS)
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author maintainer
#0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 5be7a0cef3229fb3b63a07c0d289daf752545424
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026051202-disfigure-tutu-ef08@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5be7a0cef3229fb3b63a07c0d289daf752545424 Mon Sep 17 00:00:00 2001
From: Piyush Sachdeva <[email protected]>
Date: Thu, 7 May 2026 22:22:13 +0530
Subject: [PATCH] smb: client: Use FullSessionKey for AES-256 encryption key
derivation

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 <[email protected]>
Reviewed-by Bharath SM <[email protected]>
Signed-off-by Piyush Sachdeva <[email protected]>
Signed-off-by Piyush Sachdeva <[email protected]>
Signed-off-by Steve French <[email protected]>
fs/smb/client/ioctl.c +1 -1
index 9afab3237e54..17408bb8ab65 100644
@@ -296,7 +296,7 @@ static int cifs_dump_full_key(struct cifs_tcon *tcon, struct smb3_full_key_debug
 		break;
 	case SMB2_ENCRYPTION_AES256_CCM:
 	case SMB2_ENCRYPTION_AES256_GCM:
-		out.session_key_length = CIFS_SESS_KEY_SIZE;
+		out.session_key_length = ses->auth_key.len;
 		out.server_in_key_length = out.server_out_key_length = SMB3_GCM256_CRYPTKEY_SIZE;
 		break;
 	default:
fs/smb/client/smb2transport.c +26 -9
index 41009039b4cb..e8eeff9e50d6 100644
@@ -251,7 +251,8 @@ smb2_calc_signature(struct smb_rqst *rqst, struct TCP_Server_Info *server)
 }
 
 static void 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};

@@ -265,7 +266,7 @@ static void generate_key(struct cifs_ses *ses, struct kvec label,
 	memset(key, 0x0, key_size);
 
 	hmac_sha256_init_usingrawkey(&hmac_ctx, ses->auth_key.response,
-				     SMB2_NTLMV2_SESSKEY_SIZE);
+				     full_key_size);
 	hmac_sha256_update(&hmac_ctx, i, 4);
 	hmac_sha256_update(&hmac_ctx, label.iov_base, label.iov_len);
 	hmac_sha256_update(&hmac_ctx, &zero, 1);

@@ -298,6 +299,7 @@ generate_smb3signingkey(struct cifs_ses *ses,
 			struct TCP_Server_Info *server,
 			const struct derivation_triplet *ptriplet)
 {
+	unsigned int full_key_size = SMB2_NTLMV2_SESSKEY_SIZE;
 	bool is_binding = false;
 	int chan_index = 0;
 

@@ -330,12 +332,24 @@ generate_smb3signingkey(struct cifs_ses *ses,
 	if (is_binding) {
 		generate_key(ses, ptriplet->signing.label,
 			     ptriplet->signing.context,
-			     ses->chans[chan_index].signkey,
-			     SMB3_SIGN_KEY_SIZE);
+			     ses->chans[chan_index].signkey, SMB3_SIGN_KEY_SIZE,
+			     SMB2_NTLMV2_SESSKEY_SIZE);
 	} else {
 		generate_key(ses, ptriplet->signing.label,
-			     ptriplet->signing.context,
-			     ses->smb3signingkey, SMB3_SIGN_KEY_SIZE);
+			     ptriplet->signing.context, ses->smb3signingkey,
+			     SMB3_SIGN_KEY_SIZE, SMB2_NTLMV2_SESSKEY_SIZE);
+
+		/*
+		 * 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;
 
 		/* safe to access primary channel, since it will never go away */
 		spin_lock(&ses->chan_lock);

@@ -345,10 +359,13 @@ generate_smb3signingkey(struct cifs_ses *ses,
 
 		generate_key(ses, ptriplet->encryption.label,
 			     ptriplet->encryption.context,
-			     ses->smb3encryptionkey, SMB3_ENC_DEC_KEY_SIZE);
+			     ses->smb3encryptionkey, SMB3_ENC_DEC_KEY_SIZE,
+			     full_key_size);
+
 		generate_key(ses, ptriplet->decryption.label,
 			     ptriplet->decryption.context,
-			     ses->smb3decryptionkey, SMB3_ENC_DEC_KEY_SIZE);
+			     ses->smb3decryptionkey, SMB3_ENC_DEC_KEY_SIZE,
+			     full_key_size);
 	}
 
 #ifdef CONFIG_CIFS_DEBUG_DUMP_KEYS

@@ -361,7 +378,7 @@ 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) ||
maintainer
#1 lore raw

PATCH 1/1 smb: client: Use FullSessionKey for AES-256 encryption key derivation

From: Piyush Sachdeva <[email protected]>

[ 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 <[email protected]>
Reviewed-by Bharath SM <[email protected]>
Signed-off-by Piyush Sachdeva <[email protected]>
Signed-off-by Piyush Sachdeva <[email protected]>
Signed-off-by Steve French <[email protected]>
[ adapted upstream's void/hmac_sha256_init_usingrawkey-based generate_key() to 6.12's int-return crypto_shash_* form while threading full_key_size through all callers. ]
Signed-off-by Sasha Levin <[email protected]>
---
 fs/smb/client/ioctl.c         |  2 +-
 fs/smb/client/smb2transport.c | 32 +++++++++++++++++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)
fs/smb/client/ioctl.c +1 -1
index 855ac5a62edfa..8ea532cdc4302 100644
@@ -280,7 +280,7 @@ static int cifs_dump_full_key(struct cifs_tcon *tcon, struct smb3_full_key_debug
 		break;
 	case SMB2_ENCRYPTION_AES256_CCM:
 	case SMB2_ENCRYPTION_AES256_GCM:
-		out.session_key_length = CIFS_SESS_KEY_SIZE;
+		out.session_key_length = ses->auth_key.len;
 		out.server_in_key_length = out.server_out_key_length = SMB3_GCM256_CRYPTKEY_SIZE;
 		break;
 	default:
fs/smb/client/smb2transport.c +25 -7
index daf8ba2cd8a10..63907fb245e9a 100644
@@ -334,7 +334,8 @@ 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};

@@ -355,7 +356,7 @@ static int generate_key(struct cifs_ses *ses, struct kvec label,
 	}
 
 	rc = crypto_shash_setkey(server->secmech.hmacsha256->tfm,
-		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;

@@ -430,6 +431,7 @@ generate_smb3signingkey(struct cifs_ses *ses,
 			struct TCP_Server_Info *server,
 			const struct derivation_triplet *ptriplet)
 {
+	unsigned int full_key_size = SMB2_NTLMV2_SESSKEY_SIZE;
 	int rc;
 	bool is_binding = false;
 	int chan_index = 0;

@@ -464,17 +466,31 @@ generate_smb3signingkey(struct cifs_ses *ses,
 		rc = generate_key(ses, ptriplet->signing.label,
 				  ptriplet->signing.context,
 				  ses->chans[chan_index].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;
+
 		/* safe to access primary channel, since it will never go away */
 		spin_lock(&ses->chan_lock);
 		memcpy(ses->chans[chan_index].signkey, ses->smb3signingkey,

@@ -484,13 +500,15 @@ generate_smb3signingkey(struct cifs_ses *ses,
 		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;
 	}

@@ -505,7 +523,7 @@ 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) ||
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